Applied Electrochemistry and Metallurgy: A Practical Treatise on Commercial ...

Charles Frederick Burgess, Harry Bridgman Pulsifer, Benjamin B . Freud · 1920 · Historical

Applied Electrochemistry and Metallurgy: A Practical Treatise on Commercial ... by Charles Frederick Burgess, Harry Bridgman Pulsifer, Benjamin B . Freud…

Public-domain full text preserved in the Mountain Man Mining Library. Original source: archive.org.

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Applied Electrochemistry

And Metallurgy

A Practical Treatise On Commercial Chemistry, The

Electric Furnace, The Manufacture Of Ozone And

Nitrogen By High-Tension Discharges, And>

The Metallurgy Of Iron, Steel, And

Miscellaneous Metals

Applied Electrochemis'.Ry

Bt

CHARLES F. BURGESS, E.i

PRESIDSNT, NORTHSRN CHEMICAL ENOINBBBIKO liABORATORIBS

Formerly Professor Of Chemical Enoineerino And Applied

Electrochemistry, University Of Wisconsin

Past-President, American Electrochemical Society

Metallurgy

By

H. B. PULSIFER, S.B., Ch.E.

Professor Of Metallurgy, Montana School Of Mines

American Chemical Society

American Institute Of Mining Engineers

And

BENJAMIN B. FREUD, B.S., Ch.E.

Associate Professor Of Organic Chemistry

Armour Institute Of Technology

Member, American Chemical Society

Illustrated

American Technical Society Chicago

Mar 2 1922'

Ooptbight, 1020, Bt

American Technical Society

Ooptbzohtbd In Orhat Bbitain All Biohtb Bsshbybd

Introduction

THE principles of Electrochemistry are almost as old as the science of electricity itself. The phenomenon of electrolysis was discovered in 1800, and its laws were experimentally determined by Faraday in 1833; again the electrolytic cell, with its simple electrodes and conducting liquid, was very early used to accomplish the dissociation of chemical compounds in the same manner as it is now used in chemical industries; the electric furnace was really discovered almost simultaneously with the arc lamp and in its essentials is identical with it.

9 The cheapening of electrical power and the increased use of the products involved have been largely responsible for the progress along these lines, and, today, the preparation of electrolytic copper is a great industry; hydrogen and oxygen gases are now obtained by the electrolytic decomposition of water; and the method of electrolyzing fused aluminum oxide has brought the price of alum- inum to a practical basis. Again, by means of the electric furnace, several highly resisting chemical reductions have been accomplished and methods have been perfected for the manufacture of calcium carbide, silicon products, carborundum, graphite, and steel.

9 The same years that have seen such remarkable progress in Electrochemistry, have also witnessed uncommon development in that closely related art — Applied Metallurgy. The great steel works of the country, the coal- and iron-mining industries, ship-building, ordnance manufacture, sky-scraper erection, and hundreds of other fields, are hugely interested in what the skilled metallurgist discovers. Metallurgy and Electrochemistry alike attract students — following through processes in these arts at times attains the interest of a novel.

9 Finally, when by the aid of intense electrical discharges in air, even the nitrogen of the atmosphere is made available for our use, the results seem to approach the miraculous. To think of the world's supply of nitrates being augmented from the very atmosphere itself seems more Uke a dream of a Jules Verne or a Wells, than an actual twentieth century accomplishment.

9 All of these scientific marvels are intensely interesting and the treatment has been made exceedingly practical by the authors. The material is written in a clear readable style and is designed to appeal to both the trained engineer and the layman. It is the hope of the publishers that a study of this volume may widen the acquaintance of many readers with this branch of industrial electricity and stimulate their interest in the general scientific development of the world.

Contents

Applied Electrochemistry

Page

Electrochemical theory ; 2

Electrochemical cell

Faraday's laws 9

Cathode reactions i : 11

Anode reactions 12

Electroljrtic refining and recovery of metals 12

Refining copper 12

Refining of metals other than copper 14

Electrolytic recovery of metals 15

Electroplating 17

Electroplating cell 17

Factors in successful operation 19

Working solutions for principal metals , 23

Plating non-conducting bodies 25

Decomposition of salt solutions 26

Sodium chloride 26

Hypochlorites 29

Chlorine and caustic soda 31

Electrolytic hydrogen and oxygen 37

Cells for decomposing water 37

Plant equipment 40

Fused electrolytes 41

Manufacture of sodium products 41

Manufacture of aluminum 44

Electric furnace 47

PossibiUties at high temperatures 48

Comparison between electrical and fuel heating 51

Are furnace 54

Resistance furnaces 57

Calcium carbide 59

Silicon products . . 61

Carborundum 62

Graphite. : , . 64

Alundum 67

Carbon bisulphide 67

Electric furnaces in steel industry 68

Direct reduction of iron from ores. 69

Manufacture of steel from pig iron 69

Manufacture of crucible steel 70

2 Contents

Pagb

Electrical discharge in gases 76

Production of ozone 77

Fixation of nitrogen 79

Electrical fume precipitation 81

Metallurgy

Introductory 89

General metallurgy 93

Reducibility of metak 93

(Crystallization of metals 94

Hardness of metals 95

Strength of metals 96

Plasticity of metals 97

Ores 99

Sampling 101

Pretreatment of ores 104

Furnaces 109

Classification 109

Insulating materials and refractoi linings 110

Metallurgy of iron and steel 112

Blast furnace 113

Elements of construction : 115

Actual operation 116

Secondary elements of furnace plant . , . 116

Constitution of kon 118

Composition of pig iron 118

Iron and carbon 119

Fotmdry practice 122

Furnaces 122

Molds 122

Cast iron 123

Wrought iron 124

Manufacture of steel 125

Carbonizing solid iron 125

Crucible steel 126

Bessemer steel 127

Open-hearth steel 129

Ingots 133

Mechanical treatment 135

Heat treatment 139

Electric furnaces in iron and steel manufacture 142

Furnaces for pig-iron production 142

Furnaces for making steel 142

Important characteristics 145

Contents 3

Paob

Reducing copper ores 146

Oxide copper smelting — 4 146

Sulphide copper smelting 14$

Roasting copper ores 152

Reverberatory copper smelting 154

Clpnverting copper matte . 156

Refining copper metal 15t

Furnace method 167

Electrolytic method 168

Sihrer refinery for copper plant 162

Lead — silver smeltiiig 162

Relative importance. . . : 162

Lead minerals. 163

Lead ore reduction 164

Reverberatories 164

Hearth smelting 164

Pot roasting 166

Roastnaintering , '. 166

Lead blast-furnace smelting 166

Furnace features and operation. 167

Bag houses 167

Methods of refining lead 169

Electrolysing 169

Parkes' process , . . . 169

Zinc '. , 172

Ores of inc 172

Two types of roasting furnace 173

Cadmium 176

Gold 175

Placer mining 176

Milling and amalgamation 178

Cyaniding 178

Electrolytic refining 179

Miscellaneous metals , 179

h

Applied Electrochemistry

Introduction

Chemical Reactions" Chemical reactions are frequently, if not in fact almost universally, associated with changes in electrical energy. The science and art of electrochemistry deal with the relationship of electrical and chemical forms of energy. It is well known that many chemical reactions take place with the liberation of energy in the form of heat; thus when coal burns, combining with the oxygen of the air, there is a liberation of heat energy. Certain other chemical changes involve an absorption of heat energy, that is, heat must be applied to materials in order to cause certain reactions to take place. The formation of calcium carbide is an example of the production of a useful compound by heating lime and carbon to a high temperature. All chemical reactions may be classified as either endothermic — heat-absorbing reactions — or as exothermic — heat-liberating reactions.

Numerous chemical transformations also occur with a liberation of electrical energy, a fact upon which are dependent the various types of primary cells or electric batteries. EJectrical energy may, on the other hand, be made to produce chemical changes by the passage of electric current through an electrolyte, and this finds practical application in various forms of electrolytic cells.

Storage batteries constitute an important class of electrical apparatus, consisting of a certain combination of metals and electro- lyte in which the electrochemical action is reversible, that is, in passing current through the battery in one direction certain chemical changes take place, or the battery is stored or charged, and these chemical reactions take place in a reverse direction when the current is allowed to flow in a reverse direction, as when the battery

is discharged.

Range of the Subject. The fundamental units and principles

of electricity, the elementary principles of electrochemical action,

the primary cell, and the secondary, or storage, cell have already

been considered in previous articles, and consequently this article

2 Electrochemistry

will be confined to a consideration of the wider field of applied electro- chemistry, dealing with the more important practical uses of electrical energy in producing useful chemical transformations.

Electrical energy may be applied to materials by various methods, the more important of which are the following:

(1) Electrolysis, or the electrolytic change brought about by the passage of a direct current through an electrolyte-

(2) Electrothermics, or the production of chemical change through the heat effect produced by electrical means.

(3) Electrical discharge in gases.

Electrolysis And Its Applications

Electrochemical Theory

Kinds Of Conductors

All materials may be divided, first, into two classes, depending upon whether or not they conduct electrical current. If they con- duct, they are called "conductors" and if they do not, they are designated as ''insulators". In turn, materials which conduct may again be subdivided into two more classes commonly designated: metallic condvjdors, or condv/dors of the first class; and electrolytic conductors, or condvjctors of the second class.

It is important that as a basis for the study of electrolysis a clear idea be acquired as to the distinctive differences between metallic and electrolytic conductors.

Metallic Conductors. As implied by the name, metallic corv- dvetors, the metals belong to this class; and in addition to the metals and metallic alloys, there are a few other elements and various compounds which conduct in a similar manner and are therefore designated as metallic conductors. In this class of conductors the flow of current produces only a heating effect without producing chemical change.

Non-Metallic Elements. Of the few non-metallic elements which conduct, the most important is carbon, or graphite. Silicon, boron, and selenium are other elements possessing metallic conduc- tivity to some degree.

Electrochemistry 3

Chemical compounds do not as a rule coiyiuct metallically. The important exceptions include peroxide of lead, which is a con- stituent of one of the electrodes in a storage battery; magnetic oxide of iron, FcgO, which is used as an anode material for electrolytic purposes; sulphides of lead and of silver, various metallic carbides, silicides, borides, etc.

Specific Resistance. The specific resistances of the metals and metal alloys cover a comparatively limited range, a high resistance metal such as mercury having a specific resistance about one hun- dred times that of the best conductive metals, copper and silver.

It is a characteristic of the metals that the resistance varies in a minor degree with variations in temperature. The resistance usually increases with increase in temperature, or, in other words, the metals have a positive temperature coefficient. With pure metals the temperature coefficient is a constant, i.e., the resistance is approximately proportional to the absolute temperature and, if the resistance be plotted for various temperatures, the line points toward absolute zero, suggesting that if the metals could be cooled to that point they would possess no resistance and thus become perfect conductors.

With the conductive metalloids or non-metals, and with the compounds which conduct metallically, a higher order of specific resistance is encountered as well as a greater variation in tempera- ture coefficient. To the electrochemist, carbon is the most impor- tant of these conductors. Its specific resistance varies through a wide range from that of the diamond, which is practically an insu- lator, to graphite, and then to "metallized" carbon which has a con- ductivity comparable to that of mercury.

Carbon, such as is used for electrode purposes, may consist of plates made up of finely ground carbon mixed with a binding material, molded into shape and subjected to a high temperature baking. The resistance is dependent upon the quality of the carbon flour, the purity, the nature of the binding material, the pressure of form- ing, and the baking temperature. The higher the firing temperature used, the lower is the resistance and, by carrying the temperature to the highest attainable value, the material is transformed into a more conductive form known as graphite. The discovery of this method of graphitization by electric heating constitutes one of the most

4 Electrochemistry

important of the electrochemical discoveries, furnishing not only the basis of a large artificial graphite industry but also sup- plying an electrode material of inestimable value to the electro- chemist.

By data taken from various sources it appears that the' commer- cial forms of electrode carbons have values of specific resistance varying from 3000 to 10,000 microhms per cm. Graphitized elec- trodes have a specific resistance of about 800 microhms and the value for metallized carbon has been given as 480 microhms.

The so-called metallic silicon has a specific resistance which varies greatly and in an uncertain manner with increase in tempera- ture. Boron is a conductive material which has only recently been produced but which has created special interest, in that it has a temperature coefficient which is higher than almost any other known substance. A small rod of this material, which shows a resistance of over 5,000,000 ohms at 27® C, shows 46,000 ohms at 180°. The conductivity of selenium likewise possesses interesting characteristics. This element has a high specific resistance, it has a high temperature coefficient and possesses the unusual feature that it changes its resistance notably under the influence of light.

The chemical compounds which conduct metallically are char- acterized by a high specific resistance and a high negative tempera- ture coefficient.

Electrolytic Conductors. Characteristics. The most important characteristic of electrolytic conductivity is that the flow of current produces a chemical transformation. The detection of a chemical change does not, however, constitute an infallible means of deter- mining whether a material should be placed in this class, since under certain conditions the resultant chemical change may be so slight as to avoid detection!. Faraday concluded that certain fused chlorides, for example, conducted metallically, because he could detect no appreciable decomposition. The conclusion was probably erroneous, due to the fact that the products which were liberated immediately reunited to form the original substance.

Electrolytic conductors invariably consist of definite chemical compounds. It should be borne in mind that, as pointed out under metallic conductors, not all chemical compounds which conduct are electrolytic conductors.

Electrochemistry 5

Classification. Electrolytic conductors may be either fused materials or certain solutions of materials in water or other solvents. Some evidence of electrolytic conductivity has been detected in a few solid compounds, but this phenomenon is of little importance from the practical standpoint. It is with liquid conductors that electrolysis commercially applied has to deal and for practical purposes these liquid conductors may be placed in three divisions:

(1) Electrolytes consisting of substances dissolved in water.

(2) Electrolytes consisting of substances dissolved in solvents other than water.

(3) Electrolytes consisting of chemical compounds in A state of fusion.

The first group is the one of the greatest importance, since water is a great universal solvent, which, on accountof its abundance and low cost and great solvent properties, furnishes an essential material in most industrial electrolytic processes. Non-aqueous solutions, while attracting much interest from the theoretical and scientific points of view, have as yet few technical applications. A more extensive use of these solvents, however, may safely be anticipated as a result of future development.

Electrolytes consisting of fused materials have important tech- nical applications in industries such as the manufacture of aluminum, sodium, magnesium, and calcium.

Water, in a high state of purity, possesses very little conductive power; in fact it is practically an insulating material. Kohlrausch gives a specific resistance of 25,000,000 ohms per cm for freshly distilled water. On accumulating impurities by exposure to the air for some time, the resistance may drop to one-twentieth of this amount.

Similarly, sulphuric acid, in a condition of absolute purity, has an exceedingly high specific resistance, tending to place it among the insulators. If, however, a certain amount of these two non-con- ductive substances be mixed together, the result is a material which has a i)ower of conducting to a high degree. The question has naturally arisen as to whether it is the acid under the influence of the water or the water as influenced by the acid, or a combination of both, which produces the conductive power. In settling this point, we would be led into the realm of speculation and, for practical purposes in working with aqueous electrolytes, the common assump-

6 Electrochemistry

tion may be followed that it is the substance which is dissolved in the water which possesses the conductive property.

Condvdimty, One important characteristic of electrolytic conductors is that the order of conductivity is far lower than that of metallic conductors. The best conducting electrolytes, for example, have a specific resistance at least one million times as great as that of the average metallic conductor.

Another striking characteristic is the negative temperature coefficient which causes the resistance to decrease with increasing temperature.

It should be borne in mind that by no means all of the materials which dissolve in water produce electrolytes. Those chemical sub- stances which on dissolving in water become conductive have been determined by trial and by measurements. Sugar and common salt are both soluble in water. The former, however, produces no electro- lytic conductivity, while the latter does.

It has been found by trial that, in general, solutions of inorganic acids, salts, and bases conduct electrolytically, while the neutral organic compounds in solution do not conduct.

The degree of conductivity of an electrolyte depends upon a number of factors, including the chemical composition of the dis- solved substance, the amount of such substance in solution, and the temperature.

A quantitative study of the relationship between the conduc- tivity of a solution of a given substance and the amount of substance dissolved, reveals interesting and important features and furnishes the basis upon which modern theoretical views of electrolytic dis- sociation and conduction are based. However, for practical pur- poses of an elementary text, it may not be necessary to follow this line of study here.

The Electrochemical Cell

Definitions. An electrochemical cell is a form of apparatus in which all industrial electrolytic processes are carried out. It may be defined as a combination of two metallic conductors, constituting the electrodes, and an electrolytic conductor, constituting an electro lyte which joins the electrodes. A suitable containing vessel is also an essential part.

Electrochemistry

The anode is the electrode at which the current enters the electrolyte, and the cathode *is the electrode at which the current leaves the electrolyte.

The cell is inadite if no current flows, and it becomes active when the current passes, which in turn means that to be active it must be connected to an external source of electrical energy. This external energy may be obtained from any generator of direct current, such as a primary battery, a storage battery, or a dynamo.

Action Inside the Cell. Diagram of Circuit. A typical dia- gram of an active cell is shown in Fig. 1, where d is the dynamo, or other source of current; r is a rheostat for regulating the amount of current, or current density; i is an ammeter for measuring the current; and i? is a volt- meter for measuring the voltage at the cell terminals; is a switch for opening or closing the circuit. The arrows indi- cate the direction of the flow of current; a is the anode, and c the cathode.

It will be noted that the positive (+) terminal of the voltmeter is con- nected to the anode, or positive pole, at which the current enters the cell, while the negative (— ) terminal of the voltmeter is connected to the cathode, or negative pole. For this reason it is a common practice to use the terms "positive pole" and "negative pole" in place of the terms "anode" and "cath- ode", respectively. To avoid confusion, however, it is far better to employ the terms artx)de and cathode wherever possible and to learn to know instinctively that the anode designates the surface at which the current enters the electrolyte and that the cathode indicates the surface where the current leaves.

Method of Carrying Current. To determine in just what manner the electrolyte carries the current is the purpose of various theories which are not as yet capable of positive proof. It is a common con-

— ti_2ri

o

Fig. I. Diagram of Electrolytic Cell

Electrochemistry.

TABLE I Positive and Negative Radicals of the More Common Compounds

Bub8Tancb

Nsgativs Radical

Pobitivb Radical

rORMULA

Or

Ob

Anion

Cathion

AlCl,

Al

Nh4Ci

Nh4

BaCU

Ba

CaCl,

Ca

KCl

K

CdCU

Cd

MgCl,

Mg

MnCl,

Mn

NaCl

Na

HCl

H

ZnCU

Zn

HBr

Br

H

KBr

Br

K

Hi

H

Ki

K

Ba(NOa)a

2N0,

Ba

Ca(NO,),

2N0,

Ca

Hno,

No,

H

Kno,

No,

K

AgNO,

No,

Ag

H2So4

So4

2H

Cuso4

So4

Cu

MgSO,

So4

Mg

So4

2Na

Ag2S04

So4

2Ag

ZnS04

So4

Zn

K2Co,

Co,

2K

NaaCO,

Co,

2Na

K2Cio,

Cio,

2K

Koh

Oh

K

NaOH

Oh

Na

KiCrO,

CrO,

2K

KCraOi

CraOy

2K

Kcn

Cn

K

K4Fe(CN) .

Fe(CN) ..

4K

KAg(CN)2

Ag(CN)2

K

K2c;o4

C2O4

2K

Nq.CaH,02

C2H,02

Na

Aluminum chloride

Ammonium chloride. . . .

Barium chloride

Calcium chloride

Potassium chloride

Cadmium chloride . '.

Magnesium chloride. . . .

Manganese chloride

Sodium chloride.

Hydrochloric acid

Zinc chloride

Hydrobromic acid

Potassium bromide

Hydriodic acid

Potassium iodide

Barium nitrate

Calcium nitrate

Nitric acid

Potassium nitra*e

Silver nitrate

Sulphuric acid

Copper sulphate

Magnesium sulphate

Sodium sulphate

Silver sulphate

Zinc sulphate

Potassium carbonate. . . .

Sodium carbonate

Potassium chlorate

Potassium hydroxide. . . .

Sodium hydroxide

Potassium chromate. . . . Potassium bichromate. . .

Potassium cyanide. .

Potassium ferrocyanide. . Potassium silver cyanide.

Potassium oxalate

Sodium acetate

ception that the current in passing through the electrolyte causes a bodily movement of some of the material in the electrolyte in the direction of the current and of a corresponding amount of other material in the reverse direction. Or, in other words, the materials held in solution dissociate into ions. Those ions which travel with the current and are deposited on the cathode are called cathions and those which go against the current and are liberated at- the anode are anions.

Electrochemistry 9

Anions and Cathions. In order to determine what action will take place in a cell, it is important to know what materials constitute the anions and cathions.

From a study of chemistry, it is noted that the inorganic com- pounds such as are taken into solution in water, are composed of what are known as the metals or positive, radical and an equivalent a, or negative, radical. Table I gives a list of the more common materials with their respective anions and cathions.

From this table it is to be noted that the cathions consist almost entirely of metals, with the addition of the element hydrogen and of the compound NH; also that the anions consist of the electronega- tive elements, such as chlorine, bromine, iodine, and fluorine, and of various compound radicals, such as SO, NO3, CO3, OH, CrO, etc.

Faraday's Laws. The most important laws pertaining to elec- trolysis are what are known as Faraday's laws. They constitute the basis of all electrochemical calculations, dcftermining just how much chemical action is produced by a given flow of current for a given time. These laws are as follows:

(1) The amount of chemical effect produced during electrolysis is directly proportional to the product of the current and the time; that is, to the quantity of electricity which flows through the electrolyte.

(2) When a current passes through an electrolyte, bringing about chemical changes at the electrodes, the quantity of each substance formed is directly proportional to the equivalent weight of the substance arid to the quantity of electricity which has flowed through the electrolyte.

It is obvious that if one ampere flowing for one minute will deposit a certain amount of copper, two amperes flowing for one minute will deposit twice that amount. Also that the amount which a given current will deposit in ten minutes is ten times as great as will be deposited by the same current in one minute.

Electrochemical Equivalent. By knowing the equivalent weight,

jg or, as it is more commonly termed, the chemical equivalent, of the material, the quantity of that material which will be liberated by a known amount of electric current can be readily calculated. Every

substance, whether it be a chemical element or a chemical compound, has its electrochemical equivalent, just as it has a certain atomic

he ler

)n

Electrochemistry

TABLE II Constants of the Elements*

Name of Elements

Nitrogen. . Oxygen . . . Platinum. Potassium. Silicon. . . .

Silver,

Sodium . . . Sulphur. . . Tin

Zinc.

Aluminum. . . Antimony. . . .

Arsenic

Barium

Bromine

Cadmium

Calcium

Carbon

Chlorine

Cobalt

Copper

Fluorine

Gold

Hydrogen: . . . .

Iodine

Iron

Qq

Chemical Constants

o

Lead.

Magnesium. . Manganese. . .

Mercury Nickel. .

Al

Sb

As

Ba

Br

Cd

Ca

Co

Cu

F

Au

H

Fe

Fe

Pb

Mg

Mn

Mn

Hg

Hg

Ni

Ni

N

O

Pt

K

Si

Ag

Na

S

Tn

Tn

Zn

Ob

Electrochemical Constanta

a.

pCgQ

it'

9.03.09354 40.07.41509 25.00.25898 68.70.71166 79.96.82831 56.20.59229 20.05.20770

3.00.031077 35.45.36723 29.50.30559

r Sua

Commercial Constants "Result"

u

200.002.0718 100.001.0359

,50448

§se3

&.9

n

22. Us

*From "Electrothermal and Electrolytio Industries", Ashcroft.

weight; and in fact the electrochemical equivalent is closely associated with the atomic weight.

The electrochemical equivalent of a substance is the atomic weight divided by the valence and multiplied by a constant. This constant is a weight of hydrogen which will be liberated by a unit quantity of electric current. This constant is .00001036 grams, being the

Electrochemistry 11

amount of hydrogen which is liberated by one coulomb or one ampere flowing for one second.

For purposes of practical calculation it is common to express the electrochemical equivalent of a substance in terms of the amount of material which is deposited by one ampere flowing for one hour's time. Table II gives electrochemical equivalents of various com- mon elements.

If, for example, it is desired to know how much copper will be deposited by ten amperes flowing for two hours, a simple calculation based upon the value of copper shown in Table II can be made. It is 10X2X1.1859, or 23.71 grams. Likewise, the same amount of current will liberate 10X2X1.322, or 26.44 grams of chlorine.

Cathode Reactions. In observing the changes which take place at the cathode during electrolysis, various phenomena may be noted. If a suitable solution containing copper or nickel is used, copper or nickel will be deposited at the cathode, coating it over and growing to such thickness as is determined by the amount and duration of the current. Likewise, various other metals, such as gold, silver, iron, zinc, cobalt, and cadmium, may be deposited. This furnishes the basis of the electroplating industry. Some of the metals, on the other hand, will not be deposited out in the metallic state ; for example, no one has yet succeeded in depositing metallic aluminum, neither can sodium, or potassium, or calcium, or various other highly positive metals be deposited from aqueous solutions. The reason for this is that these electropositive metals, at the instant they are liberated by the current, react chemically with the water to form other com- pounds. When sodium is deposited, it reacts chemically with the water, in accordance with the following equation:

Na+HjO=NaOH+H

Instead, therefore, of metallic sodium being liberated, hydrogen is evolved and caustic soda is formed in the electrolyte. The electro- lytic production of caustic soda and of hydrogen is thereby made possible as a result of electrolytic action supplemented by chemical action.

It should be noted, therefore, that the cathion may be deposited directly on the cathode, or it may unite chemically with the elec- trolyte.

la ELECTROCHEMISTRY

Anode Reactions. In a similar manner the anions, upon being liberated, may be deposited on the anode, or may escape as a gas, or may react chemically with the electrolyte, or may miite chemically with the electrode material. Which of these various processes takes place depends largely upon the peculiar characteristics of the material involved. It is important to note that the materials at the instant of liberation are in a particularly active chemical condition, or in the nascent state. Perhaps the most noticeable action at the anode is a tendency for the liberated materials to attack or corrode the anode. Thus, for example, when a sodium chloride solution is electrolyzed between two iron electrodes, the chlorine which is liberated at the anode will attack the iron to form soluble iron chloride; in other words, the iron will go into solution. If it is desired to decompose salt for the production of chlorine, an insoluble anode material must be selected. Graphite is particularly service- able for this purpose and is extensively used for chlorine production.

Soluble and Insoluble Anodes, We have then what are known as soluble and insoluble anodes, depending upon whether they with- stand the action of the electrolysis. As a general rule, the metals are corroded when used as anodes. It is for this reason that deteriora- tion of water and gas pipes takes place in the city streets where leakage current from electric railways flows from the iron surfaces into the earth. Dependent upon the anode solubility, the amount of metal in an electroplating solution is maintained at a constant value, the metal going into solution from the anode at the same rate that it is deposited out at the cathode.

Of the various metals, platinum is the one most commonly used when an insoluble metal is required. Graphite is insoluble in chlor- ide solutions, while it is slowly attacked in certain other solutions. Lead peroxide and the black magnetic oxide of iron, previously referred to as being compounds which conduct metallically, have their principal use in electrolytic work because of their electrochem- ical insolubility.

Electrolytic Refining And Recovery Of Metals

Refining Copper. An important use of the electrolytic cell is found in the refining of certain metals, the most important of which is copper. Copper of high purity is necessary as a conductive

-— 1

Electrochemistry 13

material for electric power generation and distribution, and in the early days of the electrical industry, the only source of a sufficiently pure metal was the native metallic copper found in the Lake Superior region and commonly known as "lake" copper. The rapidity of electrical development made this source of supply entirely inadequate and it became necessary to draw upon the enormous deposits of copper ore found in the Western States. By the ordinary metal- lurgical methods of smelting, however, only an impure grade of copper could be produced, the highest purity not being greatly in excess of 98 per cent. A very small amount of alloying impurity in copper has the effect of greatly reducing its electrical conductivity and, therefore, high purity is of supreme importance. The desire of utilizing these Western ores, therefore, directed attention to the electrolytic method of refining. In fact, practically the only known method of making impure copper available for the electrical industry is by the electrolytic refining methods which have been worked out during the last quarter of a century.

Action in Experimental Cell. A simple experimental cell for refining copper can be constructed easily by dissolving copper sul- phate crystals in water, adding a small amount of sulphuric acid, and then passing current through this solution, using an impure copper anode and a copper sheet cathode upon which the pure metal is to be deposited. The amount of copper which is deposited upon the cathode depends mainly upon the amount of current and the time of flow. The SO anion which is liberated at the anode attacks Ihe anode copper, forming copper sulphate and thus replacing the copper which is thrown out at the cathode. The amount of copper which goes into solution should, according to Faraday's laws, be equal to that which is deposited out at the cathode. The resultant action is then simply a transference of the copper from the anode through the solution to the cathode. The refining takes place because certain of the impurities in the anode are insoluble, such for example as silver, gold, and lead. Certain other impurities go into solution in the electrolyte, but are prevented from being deposited at the cathode because copper separates far more easily than do the other elements.

By-Pfoducts, The result of this refining operation is that certain of the impurities either remain attached to the anode or settle to

14 Electrochemistry

the bottom of the cell as what is known as anode slime. Other of the impurities, such as arsenic and iron, gradually accumulate in the electrolyte until such quantity is reached that it becomes necessary either to throw the electrolyte away or put it through a chemical refining operation.

The electrolytic cell for the refining of metals has been likened to a series of screens through which the desired metal is sifted, leaving the impurities behind.

While the principal object in the refining of copper was to get the pure metal, it was soon noted that some of the impurities which settled to the bottom of the tank were of value, these metals being principally gold and silver. The subsequent recovery of these materials from the anode slimes furnished a great source of profit, and, in fact, copper refining has become important not only for the manufacture of pure copper but for the recovery of precious metals as well.

Refining of Metals Other Than Copper. Silver. It must not be assumed that, because copper refining by electrolysis is eminently successful, the electrolytic method may be similarly applied to the other metals. In fact the ordinary metallurgical methods are usually superior as to cost and availability. Electrolytic silver refining is carried out to some extent by what is known as the Moehius process, in which the anodes or impure silver bars are suspended in a filter cloth sack in an electrolyte consisting of silver nitrate slightly acidified by nitric acid.

From this electrolyte the silver is deposited in a loose crystalline state which tends to grow in tree-like formations toward the anode. To prevent this, each cathode is provided with a wood scraper which periodically removes the crystalline, deposit of pure silver. This settles to the bottom of the tank, where it is subsequently removed.

Gold. Gold refining is likewise carried out to a certain extent, the anodes usually containing about 94 per cent of gold, 5 per cejit of silver, and one per cent of copper and various other metals. . The electrolyte consists of a solution of gold chloride with a small amount of free hydrochloric acid and a trace of gelatin added to improve the physical quality of cathodic deposit.

Baser Metals. While many attempts have been made toward electrolytic refining of conmion metals, such as zinc, tin, nickel, and

Electrochemistry 15

iron, the difficulties are usually so great, or the other metalliu'iz:* ical methods so satisfactory, as to make the financial reward insufficient to warrant conmiercial development. The electrolytic refining of iron seems to offer some possibilities of industrial success, due to a certain demand for a specially high-grade material. Most of the electrolytic iron thus far produced has been used only for experi- mental purposes and in researches concerning the nature of iron and iron alloys.

From the experiments of the earlier electrochemists with the deposition of lead, there was a general belief that lead could not be deposited electrolytically in anything but a loose and spongy form. As illustrating the value of a detailed study of electrolyte materials, reference may be made to the interesting and important discovery that a dense heavy deposit of lead may be obtained by the use of a solution of lead silico-fluoride, PbSiF, with the addition of a trace of gelatin. This discovery led to the development of what is known as the "Betts Process" for lead refining, which is in extensive com- mercial use.

Electrolytic Recovery of Metals. One of the alluring prospects which has been held out in connection with electrochemistry is its application to the recovery of metals from the ores. It has been thought by many inventors that the electrolytic methods might compete with the smelting and wet extraction methods constituting general metallurgical practice, but more especially have invent- ors been directing their attention to the recovery of values from re- fractory or non-workable ores discarded in current metallurgical practice.

Gold from Sea Water. It has been known for a long time that sea water contains gold in such quantity that a cubic mile of the sea water taken at almost any locality contains a great wealth of this precious metal. It is also known that gold can be deposited from an aqueous solution by the passage of an electric current, and this fact has led to many attempts at the electrolytic recovery of gold from sea water. These attempts have all been failures through neglect to recognize certain fundamental laws of electrolysis. The gold which is in solution is probably present as gold chloride, but in exceedingly dilute solution. If this electrolyte is placed in an elec- trolytic cell, the gold will migrate very slowly toward the cathode.

is

16 Electrochemistry

The sea water contains chlorides of sodium and magnesium as well as various other dissolved substances and these also act as an elec- trolytic conductor carrying the current. In passing current then through such a cell, most of the current is consumed in decomposing the more abundant materials to the exclusion of the gold. In figuring the cost of electrical energy, the corrosion of the anode material, and the interest and depreciation of the investment tied up in the cell construction, there is no possibility of a suflBcient gold recovery to repay even an exceedingly small fraction of the necessary expense.

Other Metals. Various complex ores of zip.c containing lead and silver and certain other elements have resisted treatment by metal- lurgical methods and have constituted an attractive material for electrochemical work. Many other examples may be named, but as yet no notable commercial success has been achieved in the elec- trolysis of aqueous solutions for the extraction of metals from their ores. As to the electrolysis of fused electrolytes, the conditions are different, as evidenced by the aluminum industry to bo described later.

General Features of a Recovery Process, To treat an ore or a waste product containing a metal necessitates, first, getting it into an aqueous solution. This may be done by treatment with an acid and then dissolving out the soluble compound. The next step is to treat these compounds in an electrolytic cell, depositing the metal upon the cathode from which it can be recovered. While the cost of leaching and extraction usually makes the process prohibitive, there are serious electrochemical difficulties, the chief of which is the difficulty of getting an insoluble and sufficiently cheap anode mate- rial. If a soluble anode material be employed, the expense caused by its corrosion may likewise become prohibitive.

The cost of electric energy involved is another important item. If, for example, in the deposition of zinc an insoluble anode be em- ployed, the electromotive force at the cell terminals would be at least 3 volts. One pound of zinc, for example, weighing 456 grams would require. 456 divided by 1.219, or about 374 ampere hours. At a pressure of 3 volts this makes a consumption of 3X374, or 1122 watt hours per pound of zinc. The cost of this energy would thus constitute a serious item of expense.

Electrochemistry 17

Electroplatinq

The most widely extended use of the electrolytic cell is in the art of electroplating. This is the art of coating a surface with a thin layer of dense adherent metal. Gold and silver are used mainly on account of the ornamental properties of these metals, while zinc is employed mainly on account of its protective action. Nickel has both ornamental and protective properties, and in fact each one of the metals capable of deposition has certain properties which give it some value in the electroplating art.

By Simple Immersion. As differing from the art of electro- deposition, we have jyhat is known as the coating by simple immer- sion, whereby one metal may receive a deposit of another metal by simply dipping it into a solution containing some of the latter metal. For example, in dipping a piece of clean iron into a copper sulphate solution, a coating of copper is quickly produced. Copper when dipped into certain silver solutions, likewise attains a silver coating; and coatings of gold are applied to brass by this same method in the manufacture of cheap jewelry.

Coatings obtained by simple immersion are of little practical importance, however, due to the fact that the coatings at best are either exceedingly thin or are laid down in a porous and non-ad- herent condition. It is practically impossible to secure an adherent diu-able coating of copper on iron by this method. In fact, it is a general purpose of the electroplater to avoid solutions which will produce deposits by simple immersion without the aid of the electric current.

Principles Of Electroplatinq Process

Electroplating Cell. The electroplating cell consists usually of a tank or containing vessel for holding a suitable solution of the metal to be deposited. Metal bars from which the anodes are suspended are placed above the tank. These are connected to the positive lead of the dynamo or other source of current, while the bars from which the cathodes are suspended are connected to the negative lead from the dynamo.

It is customary to place an adjustable resistance or rheostat in series with each tank, so that the amount of current flowing through the tank can be adjusted in accordance with the amount of cathode surface. It is highly desirable, though by no means common prac-

18 Electrochemistry

tice, also to include an ammeter In series with each tank for measur- ing the current flow.

Current Supply. The current supply for plating may be derived from primary batteries, from storage batteries, or from a low voltage dynamo. The earlier art of electroplating was dependent almost entirely upon primary batteries, but the greatest advance in the art came with the introduction of the electric dynamo, whereby the cost of electrical energy was enormously reduced. For small scale and experimental work, a battery source may be most convenient; but for technical work, one of the highly efficient types of plating dyna- mos must be employed.

The voltage at which the dynamo must run is from three volts

to six volts and sometimes even higher, dependent upon the general nature of the work to be done.

The low voltage plating dynamo is in general similar to the direct-current dynamo used for lighting and power purposes and diifers in detail mainly in having a very large brush and commutator surface for carrying away, with as little heat as is possible, the large volume of current which is generated.

To give a large commutator and brush bearing surface, plating dynamos are frequently constructed with two commutators. Fig. 2 illustrates a modern type of plating dynamo. The leads running from the dynamo to the various tanks are usually of a very heavy

Electrochemistry 19

copper wire or bar suitable for carrying a large volume of current without beating and to produce a minimum drop in voltage.

Fig. 3 sbows tbe method of connecting a number of plating tanks fed from one dynamo.

Anodes. The anodes which are usually employed are of tbe soluble type and consist of the metal which it is desired to plate. In some rare cases an insoluble anode may be employed but this always involves a progressive change in the composition of the solution and interferes with simplicity of operation.

Factors in Successful Operation. In General. As to the gen- eral methods of operation, the electroplating process is simple, the metal being laid down by the action of the electric current, the thickness being dependent upon the amount of current and the length of time that tbe current flows. The process of electroplating is, however, beset with innumerable diflBeulties which the plater must know how to avoid. Much of the necessary information may be found in the various textbooks, but the successful practical plater is dependent largely upon the knowledge gained through extensive experience.

20 Electrochemistry

Quality of Deposit. The success of electroplating depends primarily upon the physical quality of the metal deposited. While in electrolytic refining coherence and density are not of greatest

Courtetjf of Metal Indusiru

importance, density, coherence, and adherence are absolutely essen- tial for protective and ornamental coatings. In general, there is a tendency for electrodeposits to become rough, especially after attain- ing some thickness. It is possible to secure metal deposits which are fern-like or tree-like or, in fact, imitative of almost all forms of vege- tation, and to suppress these undesirable forms and to secure a dense smooth deposit constitutes much of the work of the electroplater. He finds he can regulate the quality of the deposit by various methods, such as the density of the solution, the composition of the solution, the current density, the temperature, the im- purities, and various other factors. ng 6 Curling ot Nickel 4 and 5 illustrate some of the

Depout forms which deposited metals may assume

Courtetg of Melai Indiatrf J

unless suitable precautions are observed. Each metal has inherent qualities or tendencies as regards deposition. For example, nickel and iron tend to deposit in a fine-

Electrochemistry 21

grained dense state; copper is markedly crystalline; lead, tin, and silver tend to come down in a loose spongy or leaf -like formation; while platinum almost, always deposits as an amorphous powder. It has taken about a century to develop the electroplating art to its present state in which practical working solutions are found for almost all of the metals. There is abundant opportunity, however, for further discovery of new electrolytes to overcome some of the present difficulties.

Addition Agents. A notable recent progressive step consists in the use of glucose or gelatin, or certain other inorganic materials, which, added to the ordinary plating solution, produce profound changes in the quality of the deposit.

Polishing, It is invariably desired that the resultant surface shall be smooth and polished. To secure the polish it is almost always necessary to subject the article to a buffing or burnishing opera- tion. By the use of plating baskets and by the use of certain solu- tions, however, bright nickel and other deposits may now be secured.

The electroplater must know not only how to make up his original solutions from commercial materials, but even more impor- tant is his knowledge of how to maintain his solutions in constant working condition. If the anode metal does not go into solution in an amount exactly equal to that plated out at the cathode, the electrolyte will become depleted in metal and this must be supplied by dissolving up suitable materials. Careful attention is necessary to maintain a certain degree of acidity or alkalinity, as the case may be.

Influence of Current Density. The factor which the plater has chiefly under his control is the current density. It is usually desired that the metal shall be deposited as rapidly as possible, so that the output of a given tank shall be a maximum. There is a limit, how- ever, beyond which the amount of current cannot be increased, and that is determined by the influence of the current density upon the quality of the deposit.

Each metal plating solution has a certain current density, usually expressed in number of amperes per square foot of cathode surface, beyond which the current cannot go. In nickel plating this is usually from five to ten amperes per square foot. In copper plating with a sulphate solution the current density may go far beyond this

22 Electrochemistry

figure. In general, a current density under ten amperes per square foot is employed.

If the safe current density is exceeded, it produces a discolored deposit usually termed a burned deposit, this term being employed on account of the resemblance of the coating to an actual heating effect.

Adherence. The adherence of a metal deposit depends on characteristics of the metals involved as well as upon the care in doing the work. If a metal having a high coeflScient of expansion is deposited upon one having alow coefficient, there will be a subsequent tendency for the coating to flake or peel off. This is a factor which is, of course, beyond the control of the plater; but a much more important factor which is entirely within his control is the method of preparing the surface which is to receive the plating. If this is properly done, the deposited metal may actually alloy with the metal to be coated; while if it is not properly done, the adherence will be less perfect.

The primary requisite for a metal to receive a deposit is cleanli- ness. Not only must the surface be freed from ordinary dirt, grease, rust, paint, or the like, but it must be chemically free from oxides or other tarnishing films, some of which are so thin as to be invisible. If a cleaned article is brought into contact with the hands, a con- tamination of the surface may be produced which will make a sub- sequent coating non-adherent. This illustrates the extreme care which must be employed. Oils and grease are removed by the use of a hot alkaline solution. Acid solutions and pickles are employed for the removal of oxides. Each metal has its own particular acid pickle which yields the characteristic and best results, but these details need not be considered here.

Principal Items of Expense. Grinding and polishing constitute the most costly part of the electroplating industry. It is a purely mechanical operation, by which abrasives or polishing materials are used either to remove adhering impurities from a surface or to give a surface the necessary smoothness. It is almost invariably true that during electroplating the surface becomes rougher instead of smoother and irregularities become accentuated rather than covered up. For this reason if a resultant smooth surface is desired, as smooth a surface as possible should be started with. Grinding and polishing before plating are, therefore, fully as important as the polishing and burnishing after plating.

Electrochemistry 23

The most important items of expense incident to electroplating are labor and materials. Labor is used mostly in the mechanical operations in preparing the surfaces or finishing the surfaces and in suspending the work in the tanks as well as in removing and rinsing. Where very small articles are to be handled, the labor and expense of stringing on wires would be prohibitive and for this reason there have been developed what are known as plating barrels or drums, by which a receptacle full of the small articles is rotated in a plating solution and the electrodeposit is formed while the article are in a tumbling motion.

Fig. 6 illustrates a modem type of rotary plater in which nails

Fig. 6. Modem Rotary Plating Machine CmHav Hanim and Van Winkle Company

or other small articles are plated without necessitating the stringing operation where each piece is handled separately.

Working Solutions For Principal Metals

The following paragraphs give the essential details and satis- factory working solution for the deposition of each of the more important metals.

Copper. Copper is among the metals which are most easily deposited. A large number of different solutions are employed, but tiie action of the two typical ones will be described.

24 Electrochemistry

(1) Add Copper Solution. The so-called acid copper bath may be made up according to the following formula:

Copper sulphate crystals (blue stone) (CuSO+SHgO) 2 pounds Sulphuric acid (HgSO) J to 1 pound

Water 1 gallon

Copper anodes are used with this solution, and the electrolyte being highly conductive and the anode metal going into solution readily, a low voltage is required, usually somewhere between one and two volts. This depends upon the current density employed and upon whether the anodes and cathodes are far apart or close together.

The current density is usually from 10 to 20 amperes per square foot of cathojie surface where the electrolyte is kept quiet. By rapidly circulating the electrolyte, however, much higher current densities may be employed while obtaining satisfactory deposits. With rapid circulation, current densities as high as 100 amperes and over may be employed.

This acid copper bath is used mainly for electrotyping and the deposition of copper in thick coatings. It cannot be employed satisfactorily for depositing directly on iron, because of the fact that iron throws the copper out by simple immersion and produces a loosely adhering deposit. When it is desired to copperplate on iron, the iron must be first given a preliminary coating from the so-called alkaline bath or the cyanide solution.

(2) Alkaline Copper Solution. Potassium cyanide is an exceed- ingly important chemical compound for electroplating use. It has the property of dissolving in water and then dissolving up various metal compounds, such as copper, gold, and silver, to produce excel- lent electrodeposits. The chief objection to its use is its deadly poisonous nature.

For preparing a cyanide copper bath, about pounds of potassium cyanide is dissolved in a gallon of water. Three-fourths of this solution is warmed up and in it is dissolved copper carbonate to the saturation point. About 12 ounces of the carbonate will thus dissolve. After pouring off the clear liquor, the remaining one- fourth of the original cyanide solution is added and the electrolyte is ready for use.

Copper anodes are employed and an electromotive force of from 3 to 5 volts is necessary to get the results. A current density of

Electrochemistry 26

from 20 to 30 amperes per square foot may be used, although in operating under these conditions the amount of copper deposited is much less than is indicated by Faraday's law.

Nickel. The nickel bath in most general use is a 3at\irated solution of the so-called double nickel salts. This consists of nickel ammonium sulphate [(NH)2.SONiS04+6H30], twelve ounces of which will dissolve in one gallon of water. Nickel anqcs, usually in the form of an impure cast nickel, are employed. ,

Some recent changes including the use of chlprids hiave resulted in improvements, but the old standard solutioai in almost universal use.

In starting a batch of work, it is customary to eijiply & ydltage of from 2 to 6 volts for a few minutes and then reduce t6 2 or 3 volts, or even less. A current density of less than 10 amperes b all that can be economically employed. Too high a current density results in a black or burned deposit of nickel.

The above are simply illustrations of electroplating baths and are typical of those used for the deposition of zinc, silver, gold, etc.

Plating Non-Conductinq Bodies

An interesting branch of the electroplating art has developed recently and has attracted marked attention on account of the novelty and beauty of the work which is being done. Fig. 7 shows how silver has been deposited upon glass and illustrates one of ttie numerous applications of a metal coating to a non-conductive mate- rial. Lace and other fabrics are being metallized; small animals, insects, flowers, leaves, and the like, can be coated electrolytically and thus be perpetuated in form and given the beauty of color through the range of those colors that lie under the control of the electroplater.

Rendering Surface Conductive. An essential step in the depo- sition of metals on non-conductive materials is first to render the surface conductive. This can be done in numerous ways; the best known being that illustrated by the practice of the electrotyper who takes a wax impression or mold from a form of type or metal design to be duplicated. This wax form is carefully dusted and brushed with a layer of high-grade conductive graphite, which, when applied to the mold, makes it appear like stove polish. This is the conduc-

26 Electrochemistry

tive surface which must constitute the starting point for the shell of copper which is subsequently to be deposited. For fabrics, flowers, leaves, or the like, the graphite will not adhere until first a layer of shellac or other sticky material is applied.

To avoid the use of graphite and the troublesome methods of applying, various chemical processes have been devised. A prelim- inary metal coating is obtained by dipping the article into a solution of a metal which is easily reducible. The wet surface is then treated with a reducing agent to throw out the metal, after which the plating can proceed by the ordinary chemical process. A solution of silver or platinum is suitable; phosphorus, pyrogallic acid, and various other re- ducing agents may be employed.

Plating on Glass. For plating on glass where the demand is for orna- mental effect as well as a strongly adherent deposit, the glass may be rendered conductive by applying a metal paint, such as finely ground silver in turpentine, and then heating in a reducing atmosphere, under which conditions the silver will actually fuse to the glass. After cooling down, the glassware is wired in the ordinary way and put into the plating tank ;r DepoHt on Glass where the metal is deposited to the de- sired thickness.

Courtaj/ of Mttal Industry

Decomposition Of Salt Solutions Sodium Chloride

Salt, NaCI, is a low priced and abundant material, which upon electrolytic decomposition may produce a number of valuable products for which there Is a ready market. The apparent profits have attracted numberless inventors and, out of a large number of cells and processes which have been patented, a few have attained notable industrial success.

Decomposition of Solution. As explained on pages 41 to 44, the simplest and most direct way of decomposing salt is by the

Electrochemistry

fusion process, electrolysis yielding sodium and chlorine. But the great diflBcidties have confined most of the electrolytic work to the decomposition of aqueous solutions of salt.

Illustrative Experiment. A simple experiment, easily per- formed, will illustrate one practical application of sodium chloride electrolysis. A solution of salt in water, about five to ten parts to one hundred of water, is placed in a glass or other non-conducting vessel, Fig. 8. Two graphite electrodes are inserted and a direct current is caused to flow for an hour, at a current density of from ten to twenty amperes per square foot of anode surface. After the solution has then been electrolyzed, it has remarkable disinfecting

AtiOD€

Cathode.

CI on liberation goes into sotution and 3ome escapes as qas

NaCI AtlD WATCR

m

Hydrogen escapes OS gas

Y\%. 8. Section of Electrolytic Cell Showing Decomposition of Sodium Chloride

and bleaching properties. A piece of colored cloth may be whitened, and one quart of the solution may sterilize a hundred thousand quarts of contaminated drinking water. Offensive odors may be quickly destroyed by the remarkable oxidizing power of this liquid. As a result of these properties, this electrolytic cell has a field of usefulness in laundries; in textile mills; for purification of city water supplies; for disinfecting public swimming tanks; for treatment of sewage, for hospital use, and for many other purposes. A notable achievement has been the purification of an island in New York harbor which had been for years a dumping place for garbage, and which had become a public nuisance from the odors evolved. The purification was effected by electrolyzing sea water in wood tubs, using platinum anodes, and then pumping this solution on the land.

428 Electrochemistry

On account of the simplicity and effectiveness of the process, much attention has been drawn to it, and it naturally follows that extravagant and unwarranted claims have been made for it.

The oxidizing power of the electrolyzed salt solution is depend- ent upon the presence of sodium hypochlorite, NaOCl. This is similar in composition and chemical action to so-called chloride of lime or bleaching powder, which is calcium hypochlorite, Ca(0Cl)2.

Action in Cell. A study of the chemical changes which take place in this type of electrolytic cell, shows how sodium hypochlorite and various other substances may be produced.

Na+H20 NaOH+H (1)

2NaOH+2Cl NaOCl +NaCl+H20 (2)

6NaOH+6Cl NaClOj+SNaCl+SHO (3)

While there are numerous reactions which take place, the simplest and most important are those set forth in equations (1), (2), and (3).

The primary action of the electric current is to draw the chlorine ions toward the anode, and the sodium ions toward the cathode where they are liberated in an amount to agree with Faraday's law. The sodium cannot exist in the free state in contact with water, hence the reaction (1) takes place by which hydrogen is liberated as a gas, and a solution of sodium hydrate or caustic soda is fonned. This is very soluble and diffuses throughout the electrolyte.

The chlorine which is liberated at the anode is soluble to some extent in the electrolyte, and it is only when liberated rapidly that some of it escapes as a gas into the atmosphere. There is, however, a strong affinity between chloride and sodium hydrate, and a chem- ical action shown by equation (2) takes place; that is, some sodium hypochlorite, NaOCl, is formed, together with an equivalent amount of salt and water.

If there is an excess of sodium hydrate, and the temperature is raised, the reaction becomes that shown in equation (3) where sodium chlorate, NaClOg, is formed, together with salt and water.

The conditions can be regulated so as to favor either one of the reactions. That is, either hypochlorite or chlorate can be produced at the will of the operator, by variation of temperature, density of solution, and duration of electrolysis. Both of these materials have

Electrochemistry 29

strong oxidizing power and both have important technical applica- tions.

It is evident that the decomposition of potassium chloride, KCl, may be effected in the same manner as the sodium chloride, and by its decomposition practically all of the potassium chlorate of commerce is now produced. This is a material used extensively in the manufacture of matches, explosives, and for other purposes where a strong oxidizing agent is needed.

MANUFACTURE OF HYPOCHLORITES Chemical Action. As indicated above, the production of sodium hypochlorite takes place in accordance with the equation

2NaOH+2Cl NaOCl+NaCl+HjO

As the process continues there is a steadily increasing amount of sodium hypochlorite in the solution and, like the salt, it may in turn be decomposed by the current. When this occurs oxygen is liberated at the anode. Therefore it is possible to attain only a certain strength of solution before the hypochlorite is decomposed as rapidly as formed, and for the sake of economy of energy the concentration of hypochlorite is not usually carried much beyond ten grams of active chlorine per liter of solution. In using this solution for bleaching and disinfecting purposes there is a considerable consump- tion of undecomposed salt which is necessarily lost, and which adds to the cost of the process unless a very cheap source of salt, such as sea water, is employed. The important items of cost in sodium hypochlorite production are the following: salt, which is decom- posed together with that which accompanies the hypochlorite solution; electrical energy; and anode renewal. Since oxygen is liberated at the anode, and since carbon and graphite corrode under such conditions, the anode loss may be considerable. The cost of electrolytic hypochlorite is usually greater than that at which an equivalent amount of bleaching powder can be purchased. Never- theless on account of convenience, cleanliness, and greater effective- ness of sodium hypochlorite over calcium hypochlorite, this type of cell has extensive use.

Commercial Electrolyzers. Among the types of commercial electrolyzers for hypochlorite is the one illustrated in Fig. 9. This shows a supply tank for dilute, salt solution, feeding in a steady

30 Electrochemistry

stream into the stoneware trough or electrolyzer. The overflow from this tank carries the hypochlorite solution into the larger rectangular storage tank below.

Since a pressure of about 5 volts is all that is needed between the anode and cathode, if current be taken from an ordinary lighting or power circuit, usually carrying a pressure of 110 volts, a rheostat

Fig. 9

to reduce the pressure at the cell terminals to 5 volts will be neces- sary. Since this is exceedingly wasteful of electric energy, it is avoided by placing a suitable number of cells in series so that littl*' or no rheostat regulation is necessary. This is accomplished in the apparatus illustrated by placing a number of partitions of graphite plates spaced evenly along the trough and separated by insulating cleats. The end plates are connected to the high voltage source of current.

Electrochemistry 31

This construction is illustrated diagrammatically in Fig. 10. Fourteen compartments are shown, divided by graphite plates. Each compartment acts as an electrolytic cell, the electric current flowing in at the left end plate, and the left-hand side of the next plate acts as the corresponding cathode. The right-hand side of this same plate serves as the anode for the next compartment, and so on. This construction serves as a simple method of connecting cells in series without using a containing vessel for each pair of electrodes.

The salt solution flows downward between plates 1 and 2, under plate 2 which is spaced a short distance from the bottom, upward between plates 2 and 3, over plate 3 and then downward, and so on through the eleetrolyzer. The rate of flow of the solution

Tit. 10. SwtioD of an ElHtrolytei for Salt Bolutiatu

is adjusted so that by the time it has passed through the last com- partment it has been electrolyzed to the desired strength.

Manufacture Of Chlorine And Caustic Soda

A process of far greater industrial importance than the produc- tion of sodium hypochlorite is the electrolytic decomposition of salt solutions for the manufacture of chlorine and caustic soda. The chlorine which is liberated is absorbed by lime in the manufacture of bleaching powder, or It may be taken up by lime solution to form a hypochlorite bleach liquor.

Practically all of the bleaching powder now on the market is an electrochemical product. Paper mills and other larger users of bleaching powder have installed, or are installing, electrochemical plants for this purpose. Caustic soda, which may be considered a by-product of this industry, is in great commercial demand and

32 Electrochemistry

electrolytic caustic has largely replaced the products of the old methods.

Difficulties. In order that the electrolytic cell may deliver chlorine and caustic, it is evident that the construction and opera- tion must be such as to prevent these materials coming together within the cell. Otherwise there would be formed sodium hypo- chlorite, which is decidedly detrimental; in fact the most effective test of the value of the electrolytic cell is the freedom from hypochlorite within the 'cell.

Since the cathode product is extremely soluble in the electrolyte and the chlorine liberated at the anode also has considerable solubility, the problem of keeping these prod- ucts separate is more difficult than is the separation of oxygen and hydrogen in the electrolytic decomposition of water. Several successful methods of effecting this have been devised, the principal ones being the yse of some kind of a diaphragm, and the use of mercuTy as the cathode material.

Methods. Diaphragm Cells. As illustrat- ing one of the several types of successful dia- phragm cells, the Townsend cell may be referred to. This is employed in a large plant located at Niagara Falls.

The cell construction is shown diagram-

maticatlyinFig.il. The central compartment

channel is made up of a U-shaped framework of

cement constiTiction, the sides being closed by a sheet asbestos

diaphragm B of special construction. On the outside of the dia

phragm B, perforated iron girds are bolted tightly to the framework.

On the outside of the cathode sheets are channels for the collection

of the caustic soda. The particularly novel feature of this cell is

that the two outer channels are filled with kerosene oil. The caustic

soda solution which is formed at the cathode trickles through the

diaphragm and sinks through this layer of oil and is drawn off

through outlets F. This oil together with the diaphrm is intended

Electrochemistry 33

to secure the complete removal of the caustic from the anode liquor. The brine solution to be decomposed is introduced into the anode chamber and the rate at which the solution flows through the oil is determined by the height of the liquid in this compartment with respect to the height of the oil column in the outer compartments.

The removal of the alkali is so effective that very high current densities can be used and still maintain high current efficiency. These cells can be constructed to use 2500 amperes each. The oper- ation of the cell shows a current efficiency of from 90 to 95 per cent, operating at a pressure of from 4§ to 5 volts per cell. The caustic which is drawn off from the cathode channels is a 15 per cent solution with an equal amount of undecomposed salt. The distinguishing feature and greatest limitation of all types of diaphragm cells are that the cathode solution which is drawn off consists of a mixture of both salt and caustic. A separation of these materials is necessary to put the caustic into a marketable condition and to prevent unnecessary waste of salt. This is accomplished by evap- oration, the salt crystallizing out as the solution is concentrated.

Mercury Cells. Mercury has a remarkable property when used as the cathode in a salt solution, which is of great interest from a scientific standpoint and of great value from an industrial standpoint. When sodium is liberated on most cathode surfaces, it immediately unites with the water of an electrolyte to form caustic soda and liberate hydrogen. If, however, the cathode is mercury, the mercury absorbs the sodium before it has time to react with the electrolyte. It takes it in the form of an alloy or amalgam up to several per cent of its own weight. The completeness with which the sodium is taken up by the mercury depends somewhat upon the temperature, but more especially upon the purity of the mercury.

If this lead mercury amalgam be removed from the cell and placed in another compartment, it may be made to give up its sodium by using the amalgam as the anode. The sodium then goes into solution and forms sodium hydrate and liberates hydrogen upon the cathode. A simple method for making the amalgam act as an anode is to bring in metallic contact with it an electronegative material such as carbon or graphite.

The Castner cell is one of the oldest and most successful of the mercury type. Its construction is shown diagrammatically in Fig. 12,

Electrochemistry

where it is indicated that the cell is divided into three compart- ments by two vertical partitions extending almost to the bottom of the cell, but not making a tight joint therewith. A and C constitute the anode compartments in which graphite anodes are employed. A layer of mercury rests on the bottom of the cell, making a seal beneath the two vertical partitions. The current is conducted away from the cell through the iron cathode in channel B. The current to flow through the cell must pass from the anode through the brine solution, thence to the mercury, and from the mercury through the caustic solution in compartment J5, then to the iron cathode, and thence from the cell. The sodium mercury amalgam is formed in the anode compartments and this amalgam is transferred

—

/i

V,

o

Fig. 12. Castner Mercury Cell

to the central compartment by a slow rocking motion which is given to the cell. The amalgam, therefore, surges back and forth, and while passing through the central compartment acts as anodic surface.

The actual operation of this cell introduces various complica- tions which need not be described here, but the cell has been very successful from a commercial standpoint in producing chlorine and caustic soda of high purity. An obvious limitation on the con- struction is the necessity of rocking the entire cell and this feature has been avoided in the construction of another successful type of mercury cell known as the Whiting cell.

The cell body is a stationary, massive construction of concrete in which the mercury rests in thin layers in the anode compartments.

Electrochemisthy 35

There are a number of divisions to the anode compartments and the mercury from each of these devices is discharged intermittently and in rotation into the oxidizing chamber where it comes in contact with graphite plates against which it gives up its sodium to the caustic soda solution. After the sodium has been extracted, the purified mercury is elevated by a stoneware wheel so that it flows back again into the anode compartments. The construction oF this cell is illustrated in Fig. 13, and Fig. 14 shows a large sized working plant of this construction. A cell 6 feet square takes 1400 amperes at a voltage of about 4 volts. A pure caustic is produced and, on

Fi(. 13. Crom Section of Whitins'a Elecirolytic CsU

account of the high current efficiency, there is little hypochlorite production and, therefore, small anode loss.

Relative Advantage of Mercury and Diaphragm Types. In view of the rapidly extending use of cells for decomposing salt, there is much discussion as to the relative merits of thie mercury and dia- phragm types of cells. The most important advantage of the former is its ability to produce a pure caustic soda solution, thus avoiding the expensive plant and costly operation of removing the salt from the caustic. On the other hand, the diaphragm process has the apparent advantage of cheaper cell construction, since tlie use of the costly mercury is avoided. Many other factors of lesser

Electrochemistry 37

importance must be taken into account in considering the relative merits of the two types of cells, including the depreciation, anode renewal, cost of salt, cost of power, labor, etc. Whether or not one cell has the advantage of the other depends to some extent upon local conditions.

Electrolytic Hydrogen And Oxygen

Uses of Hydrogen and Oxygen, Hydrogen and oxygen have extensive industrial applications. In addition to their many uses in chemical manufacture, these two gases are coming into extensive employment for oxy-hydrogen welding, and for other metallurgical operations. Oxygen is also used for similar purposes in connection with acetylene, and other hydrocarbon gases. Hydrogen is an excellent chemical reducing agent, and one of its large applications is for aeronautic use.

Hydrogen is, given off at the cathode as a by-product in the decomposition of salt solutions and in various other electrolytic processes, and is usually regarded as d waste product. Oxygen is of greater value. It is produced to some extent by the liquefaction of air arid its subsequent distillation. In this case it is mixed with a small amount of nitrogen but enough to prevent its most efficient use in attaining high temperatures in combustion operations. The pure gas can be made most economically by the electrolytic method, and the simultaneous production of both oxygen and hydrogen constitutes a profitable electrolytic industry.

Cells for Decomposing Water. Electrolytic cells of various types have been developed. They all employ either a sulphuric acid, or a sodium or potassium hydrate solution as electrolyte. Where the acid solution is used, lead is the material used in the cell construction; while with the alkaline electrolyte, iron is employed. This choice of materials is made because of the insolubility of lead and of iron in the respective solutions. It is obvious that insoluble anodes must be employed to allow the escape of oxygen.

Sepdration of Gases. An important point to be attained in water decomposition is that the anode and cathode products be kept as completely separated as possible. The bubbles of hydrogen coming off the cathode surface must not mingle with the oxygen bubbles from the neighboring anode surface. Otherwise impurity

Electrochemistry

of products results and, what is of greater importance, a liability of explosion is produced. Numerous fatalities have resulted through inadequate precaution in this respect.

The electrodes must be placed as near together as practicable to reduce the resistance and the power consumption to an economical figure.

A 20 to 30 per cent sulphuric acid solution has a better conduc- tivity than a 10 to 25 per cent alkali solution. On the other hand

t!=

Fig. 15. Sections of Schoop Electrolyser

it takes a somewhat higher electromotive force to liberate oxygen and hydrogen from the former solution, so that electrolyzers using the caustic soda or caustic potash have a slightly lower energy consump- tion than have those using the acid. The current efficiency ap- proaches close to 100 per cent; that is, the oxygen and hydrogen are liberated in almost exact accord with Faradays laws. This is essen- tial to produce gases of the highest purity — about 99 per cent pure. Since the acid or alkaline is added to the electrolyte to give the conductivity to it and water alone is decomposed, it is necessary to add distilled water from time to time to replace that electrolyzed.

Electrochemistry 39

Types of Cells. Among the various types of electrolyzers em- ployed are the following:

Schoop. The Schoop system uses sulphuric acid and cylindrical lead-lined vats containing a number of vertical electrodes. These are in the form of long tubes filled with fine lead wire to increase the

active electrode surface, each electrode being surrounded by a cylin- drical tube of non-conductive material open below and perforated toward the bottom to allow the flow of current. The gas generated inside of this tube passes upward, where it is collected. This appa- ratus is illustrated in Fig. 15.

Schmidt. The Schmidt electrolyzer uses an alkaline electrolyte and the construction resembles a filter press. The electrodes are iron plates corrugated and are separated by diaphragms of asbestos with rubber packing around the edges. The purpose of this dia- phragm is to keep separate the anode and cathode gases.

40 Electrochemistry

Schuckert. Another illustration of the alkaline type of cell is known as the Schuckert. In this an iron trough is divided into a number of oompartmenta by vertical partitions of an insulating material extending from the top three-quarters of the way down the cell. These compartments contain alternately iron anodes and cathodes. Iron hoods suspended between the partitions carry off the gases. The construction of this cell is shown in Fig, 16.

A full sized plant equipped with International Oxygen Company

ng. 1

cells is shown in operation in Fig. 17, For these cells a pressure of from to 3 volts and a current of 600 amperes is required.

Plant Equipment. An essential part of any electrolytic plant 13 a high pressure pump which is used to compress the gases into tanks for storage, although when the gases are to be used where manu- factured, large tanks such as are used in gas works may be sufficient. Precautions against explosions must be carefully observed. In oper- ating the compressor oil is not permissible for cylinder lubrication on account of the possibility of the oil getting into the oxygen and forming an explosive mixture. Glycerine is commonly employed for

Electrochemistry 41

this purpose. Among other safeguards is the use of either an iron tube kept at a red heat or a tube filled with platinum sponge or similar contact material. The gases from the electrolytic tanks will pass through such tubes and whatever hydrogen there may be in the oxygen, or whatever oxygen there may be in the hydrogen, is consumed in producing water, and the purification is thus effected.

The gases when used for blow-torch purposes are passed through water-cooled fimnels to prevent any possibility of the flame traveling backward into the tanks.

In view of the improvements being made and the high economy of the process, the electrolytic generation of oxygen and hydrogen promises to become an industry of great importance.

Fused Electrolytes

The majority of chemical compoimds which are solid at ordinary temperatures become conductive when heated up to and beyond the melting points. The nature of this conductivity is usually electro- lytic; that is, the molten materials are electrolytes which are capable of undergoing decomposition during the passage of a direct current. The conductivity of these materials is usually of about the same order as that of aqueous solutions.

The fact that we have molten electrolytes is of considerable technical importance, for upon it is based the recovery of various metals which would decompose water and, therefore, be unrecover- able by use of an aqueous solution. The aluminum industry is based upon the decomposition of a fused aluminum compound. The production of calcium, of sodium, and of magnesium is likewise dependent upon the decomposition of fused compounds of these respective metals.

Manufacture Of Sodium Products

Fused Salt. The chemistry of the decomposition of melted salt is much simpler than is the chemistry of decomposition of aqueous solutions of salt. The electrolyte consists of only two elements: sodium and chlorine. Salt can be melted at a temperature of about 900® C. (a bright red heat). When placed in a suitable container and with an anode of carbon and graphite and a cathode of iron or other suitable metal, the sodium is liberated at the cathode and the

42 Electrochemistry

chlorine at the anode. These two elements being liberated have nothing with which to react, as in the case of aqueous solutions, and they will thus be recovered in the free state.

The simplicity of this process is, however, apparent rather than real when considering the various practical difficulties which are encountered. These difficulties depend upon the high temperature, . under which condition the sodium vaporizes and has to be cooled by some suitable method. Such suitable method, however, has not been worked out technically. The chlorine which comes off at the anode being very hot is correspondingly active and the collection Mid cooling of this material presents difficulties. Also the construc-

tion of a containing vessel which will resist the attack of fused salt as well as of the liberated sodium and chlorine, is not a simple matter, and the practical difficulties have defeated many attempts to carry out this process.

Acker Process. Perhaps the most successful attempt has been the so-called Acker process, which was used for a number of years at Niagara Falls. In this process the fused NaCl was electrolyzed in a cast-iron cell of peculiar construction and lined with magnesia bricks. A cross section of this cell is illustrated in Fig. 18.

The cathode covering the bottom of the cell is fused lead above which rests a 6-inch layer of molten salt S and dipping into thig: are; a number of graphite anodes E with terminals coming yp tbjuglt the tile roof of the cell T.

This process works upon the interesting principle that, when sodium is liberated upon molten lead, it alloys with the lead, forming

Electrochemistry 43

an amalgam similar to the amalgams of sodium and mercury of the mercury process. To prevent the amalgam becoming too rich in sodium, the sodium is continually extracted from the molten metal by blowing steam through it by pipe F, as indicated in the right portion of the diagram. The steam on coming in contact decomposes the sodium to form sodium hydrate, NaOH, and liberates hydrogen. The molten caustic soda thus produced flows out of the cell through at 2). The reaction between the steam and the amalgam is violent and causes a vigorous circulation of the molten lead.

The chlorine which is liberated in the anode is drawn off from the anode chamber \inder a slightly reduced pressure by means of a fan. This causes some inflow of air through the crevices in the cover and the gaseous products thus drawn off consist of one volume of chlorine to about ten times the volume of air, the chlorine being then extracted from this mixture by means of lime to form the com- mercial bleaching powder.

These cells took about 800 amperes at a voltage of about 7 volts, the current efficiency being about 93 per cent.

The anodes were found to have a high durability unless a con- siderable amount of impurity was in the salt; the presence of sul- phates, for example, causes anode corrosion.

The caustic soda produced from this cell is in a fused condition, which on solidifying furnishes a marketable product without the necessity of evaporation involved by the aqueous electrolytic methods.

The high temperature difficulties and the difficulties of cell con- struction have apparently made it impossible for the fused electro- lytic cell to compete commercially with the aqueous methods of sodium chloride decomposition, although future improvements may reverse this condition.

Metallic Sodium. In the manufacture of metallic sodium the electrolytic methods have replaced the older chemical methods and the success has been dependent upon the use of a fused electrolyte which melts at a point much lower than that of salt. The process in most general use is the Castner process, which employs molten caustic soda, NaOH. This is contained in an iron vessel. Fig. 19. In this apparatus there is an extension below the cell for the cathode rod D and it becomes sealed by the solidifying of some of the sodium

44 Electrochemistry

hydrate at G. The cathode may consist of any one of several metals, iron being preferable. A cylindrical nickel anode C surrounds the cathode and between the electrodes is suspended a cylindrical screen of iron gauze. This prevents the sodium globules which are liberated on the cathode from floating over to the anode. The sodium which floats to the surface is ladled out periodically from F through the cover. For successful working, the temperature should be main- tained by external heating as low as possible — not more than 20 per cent above the melting point of the material. The somewhat impure material commonly used has a melting point of about 300° C.

A single cell holds about 250 pounds of molten NaOH, takes a current of 1200 amperes at about 5 volts, and works at a current efficiency somewhat less than 50 per cent.

MANUFACTURE OF ALUMINUM Aluminum is a metal which a half century ago was almost a chemical curiosity but which has now become one of the common and most useful metals in every day service. Although aluminum is one of the most abundant of the elements constituting the earth's crust, it has been locked up so tightly in combination with oxides, silicates, fluorides, and the like, that it has resisted until recently all efforts to isolate it in the metallic state. This has been finally accomplished in a practical way by electrolysis of fused aluminum compounds.

Electrochemistry 45

This element is found as an important constituent in most clays, but the known methods of extraction do not yet permit the use of such materials as an aluminum ore. Bauxite, which contains a high per cent of aluminum as hydrated oxide, is used almost exclusively in this industry, but to adapt jt to the electric furnace requires, first, a chemical purification to remove such objectionable elements as iron, silicon, and titanium, after which process the material to be treated consists of a pure aluminum oxide, AlO,.

The history of the aluminum process is interesting in that it records the almost simultaneous discovery of similar processes in America and in Europe. To Mr, Charles M, Hall is accorded the honor of working out the method commonly used in this country and by which the entire consumption of aluminum in America is supplied.

Hall Process. Type of Cell. The typical electrolytic cell, Fig, 20, may consist of an iron box about 6 feet long, 3 feet wide, and 3 feet deep, lined with a thick layer of conductive carbon. This layer prevents the fused material from coming in contact with an iron container and it also acts as the cathode terminal of the cell. The anode consists of a multiplicity of carbon rods 3 inches in diameter, suspended vertically in rows and numbermg perhaps 40 to 50.

46 Electrochemistry

Solvent for Aluminum Oxide. The important discovery upon which this process is based was in jBndmg a suitable solvent for the aluminum oxide. Such solvent was molten cryolite, being a com- bination of sodiimi and aluminum fluorides, represented by formula SNaF-AlF,. Calcium fluoride, CaF,, is also added on account of its influence on the fusibility. This molten material readily dis- solves a certain amount of the aluminum oxide, constituting a true electrolyte which undergoes decomposition upon the passage of the current.

A layer of charcoal is placed on top of the molten bath to protect it from oxidation, and the dry aluminum oxide is fed through this layer to replace that decomposed.

Action of Current. A cell, such as described, takes about 10,000 amperes of current at a pressure of 5.5 volts or upward, depending upon the condition of the bath.

In this cell the current serves a double purpose of heating the bath and keeping it in the proper molten condition for electrolytic decomposition. The aluminum is deposited on the carbon bottom constituting the cathode. At the working temperature the metal is molten and having a greater specific gravity than the electrolyte stays on the bottom. After it has accumulated to a suitable amount, it is tapped off.

At the carbon anodes a corresponding amount of oxygen is liberated and, at the temperature necessary for operation, this oxygen unites with the anode carbon to form carbon monoxide, a gas which on rising upwards burns in contact with the air to COj. The com- sumption of carbon may thus amount to from .5 to .7 of a pound, although on account of the action of the air on the heated carbon anodes and the scrap anodes which are produced, the consumption may run up to about one pound for each pound of material. The current efiiciency is reported as being from 70 to 80 per cent. The energy consumption is stated to be about 23,000 kilowatt hours per ton of metal, or stated in other terms, one electrical horsepower a year will produce about oncKuarter of a ton of aluminum.

Electrolyte. The electrolyte consists in the main of a number of compounds, chiefly sodium fluoride, aluminum fluoride, and aluminum oxide. It is a well-known fact in electrolysis that that compound in the electrolyte which has the lowest decomposition

Electrochemistry 47

pressure will be the first one'to be decomposed by the current. The following figures show why it is that the aluminum oxide undergoes decomposition rather than the sodium fluoride or the aluminum fluoride:

NaF — 4.7 volts, decomposition pressure AIF3 — 4.0 volts, decomposition pressure AljOg — 2.8 volts, decomposition pressure

If during electrolysis there is an exhaustion of the aluminum oxide, the aluminum or the sodium fluorides may then be decomposed; this also happens to some extent if the current density is run too high.

The increasing denaand for aluminum promises to make this industry of increasingly greater importance and this will be accentu* ated as the price is reduced. A scarcity of suitable ores is becoming felt and increased attention is being given to the extraction of kaoliu and othei* cheaper and abundant materials.

Electric Furnace

The use of electrical energy for the production of useful heat is becoming revolutionary not only in the field of metallurgy or tech- nical chemistry where heat is utilized, but also in its effect upon the electric power industry. It is furnishing a load for power stations, or in other words a market for their product. Where heat from electrical energy is used for low temperature operations, such as cooking, drying, soldering, and the like, it is not generally classified as a branch of electrochemistry. When, however, high temperatures are attained, we pass into what is generally considered the field of electrochemistry. There is, however, no sharp line of demarcation as between low temperature and high temperature electric heating.

The device or structure used for transforming electrical into heat energy, where high temperatures are required, is called an electric furnace. The ability of the electric furnace to attain temperatures far beyond those hitherto available by other methods gave it a dis- tinct field of usefulness in which it did not have to compete with existing furnaces. By the use of these temperatures many of nature's most closely guarded secrets have been revealed; a new chemistry of high temperatures has been evolved; new ideas as to the constitution of matter hve been developed; new methods of

Electrochemistry

preparing known substances have been formulated; our stores of avaUable materials have been enriched by the discovery of new compounds.

Possibilities at Higli Temperatures. All Sttbstances Melt In the high temperature produced in the electric furnace it has been shown that all substances can be melted. The oft encountered statement that lime magnesia, molybdenimi, tungsten, and the like, are infusible is therefore incorrect, for not only can all known sub- stances be melted, but they can be volatilized as well. These facts are full of significance and suggestion to the investigator. They show not only that there are limitations upon the materials which he may use for fiunace construction, introducing difficulties where the highest temperatures are to be developed, but that it is possible that in the melting and fusion of materials they may undergo such transfor- mation of their physical nature as to endow them with qualities of great value. One of the most successful industrial uses of the electric furnace is tHe fusion of aluminum oxide in the form of baux- ite, resulting in the production of that physical form of the material designated by the trade name *'alundum". This is a duplication of Nature's process for producing corundum, but the artificial product has marked advantages over the natural material in purity, cheap- ness, strength, and toughness, which give it greater value for abrasive purposes.

The fusion of quartz has produced a valuable material for a new kind of glassware which is indestructible by rapid or extreme varia- tions of temperature. Various refractory materials have their refractory qualities increased by melting and subsequent cooling. Experimental investigation in this direction has only begun, but the results already obtained point to many improvements which may be made in materials for furnace construction, materials resistant to chemical corrosion, and materials possessing high heat and electrical insulating properties. The volatilization of elements and compounds at high temperatures gives new methods for the purification and separation of materials, enabling the process of fractional distillation to be applied to all substances.

Behavior of Carbon. It has been shown that carbon is capable of conversion into its various forms, a fact industrially utilized with great advantage by the International Acheson Graphite Company

Electrochemistry 49

in making graphite and graphitized electrodes from the ordinary forms of coal and coke. Moissan has demonstrated the possibility of changing carbon into the diamond, and has reproduced, artificially, all the varieties of diamonds which Nature furnishes, alike in all respects save size.

All the oxides which had hitherto been regarded as irreducible have been reduced through the use of the electric furnace. Upon experiments which he has made, Borchers based the claim that carbon is capable of taking the oxygen from any known compound at temperatures within the range of the electric furnace. Similarly, other reducing agents may be made effective, and the decomposition can be produced even without any reducing agent whatever by utilizing the electrolytic action of the current. This has resulted in unlocking various of Nature's stores, making available for use such materials as aluminum, magnesium, calcium, sodium, potassium, chromium, silicon, and many others which previously could be obtained only with great difficulty if at all.

Carbides. Moissan's classic researches show us that a large number of elements imite with carbon to form carbides, miany of which were not known before the day of the electric furnace. Based upon this fact, though resulting from the independent discovery of the American inventor, Willson, the calcium carbide industry has been developed, and today thousands of tons are being produced annually. The reaction of this carbide with water forms the hydro- carbon, acetylene, which, although now finding its chief use as an illuminant, i3 capable of being transformed into other hydrocarbons. Manganese carbide reacts with water to form hydrogen and me- thane; thorium carbide gives ethylene; and cerium and uranium carbides yield liquid and solid hydrocarbons as well as the gaseous ones. Although the hydrocarbons other than acetylene have not been produced commercially, scientifically it is possible to produce petroleum and other like compounds. Such discoveries as these point to the great and significant fact that the whole field of organic chemistry offers itself as an incentive in the exploitation of the electric furnace.

Another class of carbides, such as those of silicon, boron, chrom- ium, molybdenum, tungsten, and titanium, are stable, not only resisting the attack of water but being extremely resistant to the

50 Electrochemistry

most active chemical agents. The first of these, silicon carbide, or carborundum, has found extensive application as an abrasive, and its use has led to the development of a new industry. Its extreme hardness, approaching that of the diamond, and the refractory nature of it and similar carbides, together with properties which may yet be discovered, point to the probability as well as the possi- bility that other carbides will have quite as extensive industrial application.

Related Compounds. Moissan and his contemporaries have shown that silicon, boron, and nitrogen, may be made to act like carbon in producing silicides, borides, and nitrides, each new com- pound having its own peculiar properties; and that the field may also be extended through the manufacture of the more complex com- pounds, such as the silico-borides, silico-carbides, boro-carbides, etc.

A contemplation of such possibilities is most bewildering, and to quote from an acldress by Professor Jos. W. Richards referring to electrometallurgical progress, We are so overwhelmed by new things of possible use to science or industry, that we can at most investigate only a small fraction of them. It is a virgin continent of undeveloped possibilities."

Advantages Of Electric Furnace

The electric furnace owes its place in the scientific and industrial world to certain characteristics which it possesses and to the advan- tages which it offers over other means of generating heat, the principal one being the high degree of temperature which is made available. An interesting comparison might be worked out showing 4:hat civili- zation progresses in a rate proportional to the utilization of heat energy in its highest degree of concentration. Each additional degree of temperature which can be produced and kept under control shows itself capable of new and useful purposes, and the electric furnace has added such an extension to the range of available tem- peratures that it has almost doubled that previously available.

Limitations* It simply requires the passage of the electric cur- rent through a conducting medium to produce heat, the mtensity of which depends upon the amount of current which passes. Inas- much as most substances retain their conductivity at high tempera- tures, the degree of intensity which is theoretically possible is unlim-

Electrochemistry 51

ited. Practically, however, limitations are placed upon it through the physical diflBculties of keeping the conducting medium and the furnace walls in place. The temperature is limited by the fusing point of the material, while it retains its solid condition; when fusion commences, the difficulties of containing the melted material begin, and the temperature is limited by the point of vaporization.

When volatilization begins, the gaseous materials escape from' the field of action, carrying away the heat, as rapidly as it is supplied to the furnace, in the form of latent heat of volatilization or energy stored up as potential chemical energy. It is true that the temperature of volatilization might be increased by subjection to high pressure, but this involves the construction of a container which can be made only of solid materials which will not fuse at the higher temperatures.

The electric arc maintained through a carbon vapor furnishes, perhaps, the highest temperature attainable, a temperature which is usually considered definitely fixed by the volatilization of carbon. On account of the limitations of our methods of measuring these high temperatures, the exact value to be assigned to the temperature of the electric arc cannot be stated, though the most satisfactory measurements give values ranging between 3600** and 4000° C. Whether or not this is the ultimate limit to be attained by electrical means is difficult to say. There is, of course, the possibility of exceeding it by maintaining the arc under a high atmospheric pres- sure, or by feeding electrical energy to the arc more rapidly than it can be dissipated by the volatilization of carbon, or, in other words, superheating the carbon vapor. Such speculation, however, is not necessary to show that the electric furnace has unbounded possi- bilities, since the range of temperatures below that of the ordinary arc offers an unlimited field for usefulness.

Comparison Between Electrical and Fuel Heating. While the attainment of high temperatures was the first achievement which called attention to the electric furnace and found manjft technical uses for it, the later developments have been in the direction of using electrical heating in competition with the various metallurgical proc- esses where the combustion of fuel is employed. There are some who doubt the ability of the electric furnace to make inroads upon the fields occupied by other types of furnaces, and maintain heat energy from electricity to be entirely too costly, arguing as follows:

52 Electrochemistry

TABLE in Relative Fuel Costs

Source of Heat

B. t. u. at Cost of One Cent

Coal at $2.50 per ton

112,000 B. t. u.

45,000 B. t. u.

32,000 B. t. u.

37,500 B. t. u.

6,000 B. t. u.

340 B. t. u.

3,400 B. t. u.

13,600 B. t. u.

Natural eas at 20c oer M

Oil at 4c sallon

Producer sas at 4c per M

City illuminatiiific cas at Sl.OO per M

!Electrical enerirv at 10c per kw. hour

Electrical enercv at Ic per kw. hour

Electrical eneriey at ic per kw. hour

Cost of Heat from FiLels, A cheap source of heat energy is coal. On the assumption that one ton of a good grade of coal costs $2.50 and during combustion liberates heat to the extent of 14,000 B. t. u. per pound, the quantity of heat available for one cent will then be 112,000 B. t. u. From producer gas at four cents per thousand cubic feet and containing 160 B. t. u. per cubic foot, the heat attain- able for one cent is 37,600 B. t. u. \yith city illuminating gas, of a calorific value of 700 B. t. u. per cubic foot and costing $1.00 per thousand cubic feet, we have 6000 B. t. u. available at a cost of one cent.

Cost of Heat from Electrical Energy. Electrical energy as dis- tributed for lighting purposes costs in the neighborhood of ten cents per kilowatt hour. Vhen freed from the cost of distribution and if delivered in large quantities without expensive transmission, this energy may be obtained for from one to two cents per kilowatt hour and from waterpower plants it is being sold at even lower prices, two cents per kilowatt hour being near the low limit. One kilowatt hour of electrical energy, when transformed into heat, furnishjBs about '3400 B. t. u., or, in other words, the heat equivalent of one kilowatt hour is represented by this figure.

Table III gives an idea of the relative cost of heat units obtained by different methods.

From Table III, it is evident that electrical heating with the lowest cost of energy obtainable is over eight times more costly than where heat is obtained from coal. The electric furnace, however, has advantages of such importance that this relative cost of heat units does not constitute a serious handicap for such a furnace. The

Electrochemistry

TABLE IV Heat Efficiencies of Furnaces

Kind of Furnace

Efficiency

For feneration of steam from coal

50% to 60%

52% to 66%

10% to 12%

5% to 8%

2% to 4%

2% to 3%

75%

75%

50% to 80%

Blast furnace for manufacture of iron

Open hearth furnace for steel

Reverberatorv furnace

Crucible steel furnace

Retort furnace for zinc

fjlectric furnace — for irraphite

Electric furnace — for fused ALO,

Electric furnace — for iron and steel

advantages of tbe electric furnace may be summarized chiefly as follows:

Electrical energy gives "pure, unadulterated heat'* to the material which is to be treated, while many of the combustion methods involve the transmission of heat by means of the gaseous products of combustion. The efficiency of electrical heating is, therefore, greater. Table IV gives a numerical idea of the heat efficiencies of various types of industrial furnaces.

10 ?0 30

Fic* 21. Loaaes of Heat in Melting Metalfl

Copied from The EUetrie Furnace, by Alfred Stansfidd

Fig. 21 gives a graphical representation of the heat lost and utilized in various types of furnaces for melting metals.

The chief reason for the very low efficiencies of combustion furnaces is that the waste products of combustion carry away most of the heat. In a crucible furnace this loss is so great that as much as 98 per cent of the heat energy is wasted. Radiation losses from combustion furnaces are usually greater than for electric furnaces on account of the larger size of the former.

54 Electrochemistry

Economy of Electric Heating. As shown in Tables III and IV, 112,000 B. t. u. are available for one cent's worth of coal, but if this heat is used for melting steel in a crucible furnace, only two per cent or 2240 B. t. u. are useful. With electric heating, however, at one-quarter cent per kilowatt hour at an efficiency of 80 per cent, 10,880 B. t. u. are actually available, and the electric heating thus becomes far cheaper even for the lower temperature metallurgical operations.

Added to this advantage of high efficiency, the electric furnace has the merit of making available high temperatures; of making possible a direct application of the heat to the material heated; of making small furnaces do the work of larger furnaces. The volumes of gaseous products which have to be handled are much less with the electric furnace, and this is also important because the gaseous products of combustion frequently interfere with the desired chemical reactions. The electric furnace can be operated with either an oxidizing or reducing atmosphere. Not the least among the advan- tages of the electric furnace is the more efficient use of refractory materials which is possible. The limitations upon almost all types of furnaces lie in the limitations of refractory materials which are available. In a crucible type of combustion furnace, the heat must pass through the refractory walls to get at the substance to be heated. This means that the heat to pass through this refractory material must have a higher temperature outside than inside. If, for example, iron is to be melted, having a melting temperature of 1500° C, the temperature on the outside of the crucible must be considerably higher than this. On the other hand, if electrical heating can be applied inside of the crucible, the crucible linings may be at a some- what lower temperature than 1500°.

Types Of Electric Furnaces

While the transformation of electrical energy into heat energy is in itself a simple operation capable of being carried on at an efficiency of one hundred per cent, there are innumerable modifi- cations of furnace construction and operation. Electric furnaces may be classified in two main classes, viz., the arc furnace and the resistance furnace.

Arc Furnace. The electric arc had its first great use for illumi- nation purposes, depending for its usefulness on the fact that an arc

Electkochemistry 55

maintained between two carbon terminals raises these terminals to such a hi temperature as to give off intense luminous radiations. Fig. 22 illustrates such an arc, main- tained by the flow of direct current. The arc itself consists of a crater at each of the electrodes and a conductive gaseous medium connecting them, the location of the highest temperature being at the pos- itive crater. This temperature is proba bly the highest attainable by any known means, being that of the vaporization of carbon.

Either direct or alternating current copudfr bv may be used for maintaining an arc and

thus we have a subdivision of arc furnaces into the direct-current and the alternating-current types.

In electric furnace terminology, the term electrodes is used in a different sense from that implied in electrolytic cells, being the terminals or conducting bodies furnishing the entrance and exit of the current to and from the furnace. Carbon or graphite is almost universally employed as electrodes for the arc furnace because of

the ability of these materials to withstand the intense heat without melting.

The arc furnace differs from the lighting arc mainly in its size and far greater power consumption and in its being enclosed within refractory walls to prevent the escape of the heat. The increased

56 Electrochemistry

power consumption is brought about by increased flow of current at only slightly higher voltages than those used in the arc lamp. The

pressure required to maintain a powerful arc furnace ranges usually between 50 and 100 volts, while the current consumption may be hundreds and even thousands of amperes,

A small arc furnace is illustrated in Fig. 23, where the terminals of two horizontal carbon electrodes are Enclosed in an iron box lined with a heavy layer of lime, magnesite, DP other highly refractory material. Such a furnace has extensive use in small laboratory operations, where the heat of the arc is radiated from the craters, reflected by the walls, and conducted by the enclosed gases to the crucible or material resting on the bottom of the furnace.

Fig. 24 shows diagrammatically the same type of furnace applied to the treatment of an ore fed contin- ually into the side of the furnace, the volatile products passing up

Vis. 26. FuTDMe with Embedded Aro , ,. ,,,.., ,

Copiidfrom Eiiciraihtrvmt siedroiiiiic the chimncy, end the liquid metal'or

Industrie, bv AihcrofC . . n- i. j.1. 1. ij.

Slag runnmg on at the bottom. Another modification is illustrated in Fig. 25, where the arc is actually embedded in the mass of material which is being treated:'

Electrochemistry 57

In this case the upper electrode consists of carbon and the lower one of the liquid metal or material which is being reduced. In such form of furnace, calcium carbide may be produced, or the reduction of iron oxide may be effected.

An arc furnace in which two arcs are maintained is illustrated in Fig. 26, where M represents a mass of molten iron covered by a layer of slag S. The current entering one of the carbon electrodes passes through the are and the slag to the iron, thence through the slag and are to the other terminal electrode. This is a type of furnace commonly used in the electric steel industry.

Resistance Furnaces. The resistance type of furnace depends upon the fact that in passing current through a conductor heat is generated, the temperature being higher the greater the amount of current. Thus heat may be generated within the material under treatment if such material has the proper degree of conductivity. Or the heat may be conducted from the conductive mass carrying the current to a surrounding or adjacent material.

The term "resistor" is used in designating that portion of a resistance furnace which conducts the current and in which the heat

S7

58 Electrochemistry

is generated. This resistor may be any one of a large variety of materials, such as granulated or crushed carbon or coke, fused

FTg. 28, SMtion of Muffle FumBce B— Cerbon rejustor plates; T— Carbon top plates; B— Graphite bottom plates: E— Graphits electrodea; S — Regulating screws and gears; A — Special rcfracloty cement; F — Fire brick beat insulation ; P— Pyrometer hole; D— DraTt hole and cover.

CoBTlesi/ 0/ Hoakim Manulaclurim) Compans

metals, slags, or, in fact, any material which is conductive in the liquid or solid state.

Electrochemistry 60

Fig, 27 shows a common type of resistance furnace, such as is used in the manufacture of graphite and carborundum. The resistor is the central column of coke, between the two terminal carbon electrodes, and surrounded by the layers of material under treatment, the whole being enclosed within the retaining walls.

Figs. 28 and 29 show a type of resistance furnace in extensive use for the heat treatment of metals and for other purposes where muffle heating is desirable on a small scale. The sectional view shows two tiers of carbon plates R, an upper graphite plate T, the carbon plates being pressed upward against this plate by graphite

Hk. 29. Hoakins Type F C Electris Furnnce Caurtetu nf Hoikini lianafaduTina Cnmpang

electrodes E. The heat is generated by the passage of the current from plate to plate, and the degree of contact is varied by the adjust- ing wheels at the bottom of the furnace. By this adjustment, and by varying the pressure of the current supplied to the furnace, the desired degree of heat can be attained.

Commercial Processes

NON-METALLIC COMPOUNDS Calcium Carbide. Lime and carbon mixed together and heated to a high temperature react according to the following equation: CaO-|-3C CaC,+CO

60 Electrochemistry

That is, the carbon acts as a reducing agent to remove the oxygen from the lime and additional carbon unites with the lime to form calcium carbide.

The temperature required to bring about this reaction is higher than can be furnished practically by combustion furnaces. Electric heating is necessary, therefore, in the production of this compound, and this use has constituted an important electric furnace industry since 1895.

Calcium carbide is a crystalline product which has the property,

upon adding water, of liberating gas according to the following

reaction

CaC2+2H20 C2H2+Ca(OH)2

This gives CgHg, or acetylene, which has its most extensive applica- tion as an illuminant and it is chiefly for the production of this gas that calcium carbide is manufactured.

The process is a simple one. The raw material consists of an intimate mixture of a good grade of lime and of carbon in the form of charcoal, coke, or anthracite coal.

There are two main types of furnaces used in the treatment; in one type the calcium carbide is removed from the furnace in the form of a solid block; in the other type it is tapped from the furnace in a liquid state.

In the former type, the heating may be effected by means of an arc drawn between two carbon electrodes, the mixture being fed to the heat zone where the reaction takes place and the molten carbide flows into a mass which solidifies in the cooler portion of the furnace. The earlier methods consisted in running a box type of furnace until a certain amount of carbide had accumulated therein, when the current was interrupted and the solidified material removed and broken up for shipment. An improvement in this type consisted in forming the calcium carbide in a rotating type of furnace as illustrated in Fig. 30. The solidified core is rotated away from the arc terminals at a rate proportional to the formation of the carbide. On the opposite side of the furnace, the core is removed by breaking off pieces. This type of furnace is an improvement which insures continuous operation.

In the tapping type of furnace, an iron container lined with a refractory material with a bottom layer of carbon contains the

Electrochemistuy 61

charge. An electrode is lowered from above, and 200 kilowatts and upward of alternating energy is supplied. The higher temperature XQaintains the carbide in a molten condition and at regular intervals it is tapped from the furnace into iron ladles.

In either the tapping type or the rotating solid core type, con- tinuous operation of the furnace is possible.

The energy consumption per pound of carbide is stated to be in the neighborhood of two kilowatt hours.

Silicon Products. Just as lime may be acted upon by carbon at high temperatures so reactions likewise take place in mixtures of carbon and silicon oxide or sand. Electric furnace temperatures are themostpractical for bringing about these reactions, of which there are several possible ones depending upon the temperature and other working conditions.

One reaction may be represented by the equation SiOj+C SiO+CO Silicon monoxide, SiO, is a brown powder. Its suggested uses are as a pigment, as a reducing agent, and as a heat insulating material. Thus far, however, it has been an unimportant technical product.

62 Electrochemistry

Another reaction proceeds according to the equation

SiO+C Si+CO

That is, the silicon monoxide may be reduced by the carbon to the element silicon with the accompanying evolution of carbon monoxide. Large quantities of silicon have been produced according to this method and a material which was formerly a chemical curiosity is easily produced in large quantities, A construction of furnace which has been proposed for the production of silicon is illustrated in Fig. 31. The electric termi- nals of the furnace consist of two carbon electrodes introduced horizontally. Connecting these electrodes is a pile of carI:on slabs acting as a resistor where the heat is generated. This resistor is surrounded by a mixture of sand and carbon and the molten silicon settles to the bottom and flows through the openings into the lower chambers. This so-called metallic silicon has a purity of about 95 per cent. It is a dense crystalline substance with a dark metallic luster. It has a melting couritavof BkciTochmicaUnAiTy point somewhat Icss than that

of pure iron. Among its uses, it is employed as an addition agent to steel and it is also manufactured into crucibles and containers for resisting acids.

Still another reaction which may take place between sand and carbon is represented by the equation

SiOj-|-3C SiC+2CO

Carborundum. The silicon carbide, SiC, or carborundum, as it is generally known, is the most important of the products obtained from the union of the reactions between silicon and carbon. It was discovered, in 1891, by Acheson, who recognized in the hard iri- descent crystal produced a material valuable as an abrasive agent

Electrochemistry 63

The hardness of this material is only slightly less than that of the diamond and it is now produced in large quantities on account of this useful property.

The electric furnace is a simple type of resistor furnace in which a conductive core of carbon about three feet in diameter is placed between the end carbon electrodes which are held stationary in fire- brick walls. Packed around this carbon core is a mixture of finely

ground anthracite coal, or coke, with a pure silica sand, mixed approximately according to the chemical formula given above. In addition to these materials some sawdust and salt are added, the purpose of the former being to increase the porosity of the charge and allow the ready escape of the carbon monoxide gas. The presence of salt is claimed to assist in the removal of some of the metallic impurities in a volatile state,

A 2000-h.p. furnace is approximately 30 -feet long and takes 6000 amperes at a terminal pressure of about 230 volts. As the core heats up, its resistance decreases so that for a constant power

64 Electrochemistry

consumptioQ an increased amperage at a lower voltage must be supplied. At the end of the run the current may be 20,000 amperes at a pressure of 75 volts.

When the reaction has been completed, the furnace is allowed to cool down, the side walls are removed, and the carborundum is found as a thick shell around the inner core. Fig. 32 illustrates one of these furnaces in the process of dismantling after a run.

In the operation of carborundum furnaces, considerable quan- tities of graphite have been produced, especially in the hotter portions of the charge. This is explained by the fact that carborundum when

heated to 2200° C, decomposes, the silicon being vaporized away, leaving the carbon in the form of graphite. According to the reaction

SiC Si+C Graphite. One of the most spectacular, as well as important, achievements of the electric furnace is the production of artificial graphite. To Mr. Acheson belongs also the credit of its developmeot. He found that at certain high temperatures carbon in the form of coal or coke is transformed into graphite. It has been the prevail-

Electrochemistry 65

ing belief that this conversion is brought about through the aid of certain oxides, sych as those of silicon, aluminum, and iron. The exact way in which these oxides act is not clear, the supposition being that they act as a catalytic agent. Artificial graphite is now produced in many different grades and the number of its uses is steadily increasing.

The type of furnace for the production of graphite powder is similar to that of the carborundum, having permanent end walls with electrodes, a fire-hrick bed, and removable side walls of refrac-

tory brick. When charging, a layer of carborundum sand is first placed on the bed to protect it from fusion. The charge is then filled in up to the lower portion of the electrodes. It consists usually of anthracite coal, ground to a varying size, A core of graphitized material is employed on account of its ability to conduct the current and serve as a resistor. Finally more of the charge is placed around and above the core and the furnace is covered with a layer of refrac- tory sand to prevent oxidation.

A 1000-h.p. furnace is 30 feet long with a core diameter of 2 feet. The current increases from 3700 amperes to 9000 amperes

66 Electeochemistry

during heating, while the voltage decreases from the starting value of 200 down to about 80. A run may be 24 hours in length, after which the furnace is cooled sufficiently for dismantling. A graphite furnace in operation is illustrated in Fig. 33.

For the manufacture of graphite in the form of blocks or rods suitable for electrode purposes, a similar type of furnace is used. The ungraphitized articles are made from a mixture of amorphous carbon or finely powdered petroleum coke, pressed and molded with a pitch binder, after which it is calcined in a gas-fired furnace.

To convert these carbon bodies into graphite simply means the application of a suflficient amount of heat, to secure which the carbons are packed between .the end electrodes of the graphite furnace in a bed of conductive granulated carbon or graphite. The operation is similar to that of the graphite furnace just described.

The industry is of interest to the electrochemist not only as being an electrochemical industry in itself but also as furnishing a most valuable form of carbon for electrolytic and electric furnace Jfork, Fig. 34 illustrates various forms of graphite electrodes while

Electrochemistry 67

Fig. 35 illustrates large graphitized carbon cylinders arranged to be fitted together for use in electric furnaces,

Alundum. Alundum is another electric furnace product which has a commercial value as an abrasive, also as a highly refractory material. Alundum is the trade name given to fused aluminum oxide. It is made by first purifying bauxite and then fusing it in an electric arc furnace. The furnace consists of a circular hearth of carbon blocks with a removable wall of sheet iron, water-jacketed throughout. Two carbon electrodes introduced from above convey the alternating current to and from the furnace. When a sufficient

quantity of the fused material has formed, the solidified material is removed and broken up, crushed, and graded.

From the finely crushed material, grinding wheels are formed, and it is also used in the construction of crucibles and muffles such as illustrated in Fig. 36.

Carbon Bisulphide. One of the big electric furnace achieve- ments is its recently attained monopoly in the production of carbon bisulphide. This is a liquid of the chemical composition of CSj. The Taylor furnace, by which practically all of the supply of mateiial used in this country is manufactured, is of the resistor type, illua-

68 Electrochemistry

trated in Fig. 37, It is a fire-brick structure, enclosed in a strong iron shell. The resistor consists of pieces of coke or of broken electrode carbons fed into and occupying the space at the bottom of the furnace, and terminal elec- trodes of carbon supplying the current to this resistor mate- rial. The form of carbon used for the resistor does not react readily with sulphur, but the contrary is true of the char- coal which is fed in at the top of the furnace and occupies most of the space in the up- right cylinder. The sulphur is introduced into the hearth of the furnace below the elec- trodes, where it is vaporized and passes upward through the charcoal where the reac- tion takes place. The carbon bisulphide vapors leave the furnace at a comparatively low temperature.

Electric Furnaces In The Steel Industry

After years of experi- mental and exploitation work, the electric furnace has reached a position of commercial im- portance in the iron and steel industry. While at present a comparatively small tonnage of steel is influenced by elec- tric furnace development, there is a general prediction that the electric furnace is going to become of great importance.

The different ways in which the electric furnace may be used in this industry may be classified as follows :

Electrochemistry 69

(1) The direct reduction of iron from its ores, producing either a pig iron or finished steel,

(2) Replacing or supplementing the existing types of metallurgical furnaces for the manufacture of steel from pig iron.

(3) The replacement of the crucible process by the electric furnace.

(4) For the heating of billets and bars, for the purpose of heat treat- ment or for rolling and drawing purposes.

Direct Reduction of Iron from Its Ores. For this purpose the electric furnace must replace the ordinary blast furnace in which the iron ore is reduced by being mixed with coke or other form of carbon, the heat for reduction being supplied by the combustion of the fuel. This type of furnace has a high thermal eflSciency, being above 50 per cent, and from the standpoint of cost of energy, the electric furnace has little opportunity for competing. The electric furnace, however, supplies heat by the transformation of electrical energy, while the heat from the blast furnace must be obtained from the combustion of the carbon in the furnace charge. Therefore, with the electric method a material saving can be made in the amount of coke or other form of carbon used, and this method is therefore advantageous where fuel is scarce and waterpower plentiful. Furthermore, a higher temperature can be obtained by the electrical method of heating so that certain refractory ores can be reduced in the electric furnace which would clog up the ordinary blast furnace.

For the successful direct smelting of iron ores there is required a very cheap source of electric power in a location where there is a market for the product, also a convenient source of iron ore, and where a saving in the amount of carbon used is of importance; in other words, where the price of coke or charcoal is high. These conditions are found in only a few places, such as along the Pacific Coast, where extensive experiments along this line have been carried out. In the industrial centers, however, the direct reduction of iron ores does not seem to be practicable by the electrical method.

Manufacture of Steel from Pig Iron. Steel is conunonly made from pig iron by taking the molten iron as it comes from the blast furnace and putting it through a refining operation, in the Bessemer or open hearth, or other similar refining process. If the refinir " not done in conjunction with the smelting operation, the pig '

70 Electrochemistry

shipped to the place where the refining plant is installed, and in this case the pig iron must first be melted up.

It is evident that there are various ways in which the electric furnace may be employed, either to replace or to supplement the ordinary refining operations. Instead of running the molten pig iron into the Bessemer converter, the hot metal may be run into an electric furnace and the refining operation carried on by the addition of the electrical heat which may raise the charge to any desired temperature. On the other hand, the electric furnace may be used only as a finishing step after a certain amount of refining has been done by the ordinary process.

Temperature is an important factor in the refining operation, and under the higher temperatures available in the electric furnace, the refining may be carried out more quickly and to a higher degree than is possible by the fuel methods of heating. For such purpose the electric heating has a high thermal efficiency as against the much lower thermal efficiency of the gas- or fuel-heated furnace; and in taking the molten material from the blast furnace or melting furnace, heated by fuels, the electric furnace is called upon only to do the high temperature, or critical, part of the work. It is claimed that by its use a specially high quality of steel may be secured and that the uniformity of the product is much greater than is otherwise attainable.

Manufacture of Crucible Steel. In the manufacture of high grade tool steel, the electric furnace seems to have its most marked field of usefulness.

The crucible process, as ordinarily carried out, consists in melting up in graphite or plumbago crucibles a commercial grade of pure iron and adding the purifying and alloying agents which are required. The crucibles, costing about $2.50 each, will hold about 100 pounds of metal and can be used six or seven times. These crucibles are heated by the products of combustion and the thermal efficiency is very low, being in the neighborhood of two per cent. The electric furnace with its 80 per cent efficiency is, therefore, able to compete profitably, and the high cost of crucible maintenance gives the electric fur- nace another opportunity to win out in the struggle for supremacy.

Arc Type of Furnace for Iron and Steel. The various forms of the arc type of furnace are playing the more important part in the

Electrochemistry 71

electrometallurgy of iron. As illustrative of the leading formg of arc furnace, reference may be made to Fig. 38, showing the Stassano, the Heroult, and the Girod methods of operation.

Stassano Furnace. This furnace in practice assumes several forms. It consists of a thick walled, rectangular chamber with a slightly arched roof. The electrodes are introduced into the side of the furnace and the raw material charged in at the ends. Tapping holes are provided for the slag and the finished steel. Another modification takes a circular form in which the entire furnace is

Stassano

Fig. 3S. ScdanB of Three Ropresentative Types ol Steel Furnaces

slightly inclined and rotated slowly about its axis so as to give some agitation to the furnace contents. The fixed type of furnace has been designed up to a capacity of 750 kw,, while the rotating furnace has a capacity of about 200 kw. This furnace operates at a pres- sure of about 150 volts, somewhat higher than is usual with arc furnaces on account of the long arc which is employed,

Kerovlt Furnace. This furnace, which , appears to be most widely used in this country, is of a simple construction consisting of a shallow hearth lined with refractory material and roofed over with silica brick. The contents are discharged by tilting the entire furnace, together with the electrode supports. Two electrodes enter

Electrochemistry 73

vertically through openings in the roof and project down to within one or two inches of the surface of the bath. They may be water cooled at the points where they pass through the roof as well as at

the cable connections. Furnaces of a capacity of from 15 to 20 tons have been used and operated at pressures of from 45 volts to 100 volts, depending upon the energy input. A 15-ton furnace requires

74 Electrochemistry

up to 2000 kw. Fig. 39 illustrates the Heroult type of furnace in operation, while Fig. 40 shows the tilting operation for discharging the finished product.

Girod Furnace. This furnace differs from the Heroult in that the current enters through the electrode in the roof of the furnace,

Fig. 41, arcs across to the slag, then through the steel bath, finally leaving by one or more steel electrodes embedded in the refractory hearth material. Thus instead of having two arcs in series there is only one. The voltage of this furnace is, therefore, approximately half that of the Heroult type and with furnaces of equal load the current is necessarily twice as great. These furnaces have been built up to capacities of 15 tons. The voltage varies between 55 and 75 volts and a 300-kw. furnace will take from 5000 to 5500 amperes and a 1200-kw. unit will take 20,000 amperes.

Indridion Steel Furnaces. An important type of steel furnace is what is known as the induction type, whereby the use of electrodes is entirely avoided, as is also the contamination of the steel by piieces

Electrochemistry 75

of carbon breaking off from the electrodes. The absence of carbon electrodes is made possible by causing the molten metal, in s con- tinuotis circyit, to carry the energy which is applied to it by magnetic induction. In other words, an induction furnace is a step-down

transformer with a short circuited secondary con.tiHting of a inf;le turn of the molten metal. Itis obvious that the molten metal muitt be confined in a channel surrounding the core of the tranHformer, which core is also wound with a winding of a suitable number of turns to correspond with the alternating voltage which is applied.

76 Electrochemistry

Fig. 42 shows the cross section of an induction furnace, C representing the iron core, or transformer, D the winding placed thereon, A the molten metal constituting the single turn secondary embedded in a refractory channel, and B the refractory cover for this channel.

To get such a furnace in operation, it is necessary that there be a continual metal mass, which is afforded by pouring molten metal into the furnace. When a pour is made from the furnace, care is taken to retain some of the metal to act as a starter for the next run.

As counterbalancing the obvious advantages, this furnace has losses and disadvantages which have restricted its general use. It is subject to magnetic and electrical losses due to hysteresis in the iron core, heat losses in the primary circuit, and magnetic leakage. Furthermore, there is a large heat radiating surface by reason of the long channel which must be employed for a given quantity of metal. Fig. 43 shows the operation of a small induction type of furnace.

Electrical Discharge In Oases

Thus far consideration has been given to the use of currents passing through solid or liquid conducting materials where compara- tively low voltages are required; also to a certain vapor type of conduction in the low voltage electric arc.

Characteristics of Discharge. A new and rapidly developing field of applied electrochemistry utilizes phenomena attendant upon the application of high voltages to gaseous media. Fig. 44 conveys diagrammatically an idea of the relation of current and voltage when an increasing difference of potential is applied to two similar elec- trodes separated by air or other gas. As the voltage is increased from zero, there is little flow of current or, in other words, the elec- trodes are practically insulated. By sufficiently sensitive instru- ments a slight flow of current may be detected, as indicated by the portion of the curve marked "non-luminous discharge". This pro- duces no physical or chemical effects and is unimportant from the practical standpoint. Upon reaching a certain voltage, however, there is a discontinuity of the curve, the current increases, and the discharge between the electrodes becomes luminous. The appear- ance and exact nature of this luminous discharge vary, being dependent upon whether direct or alternating currents are flowing.

Electrochemistry

the shape of the electrodes, and various other factors. It is desig- nated as a glow or brush discharge. The intensity becomes greater as the voltage increases, and when air is a medium, the oxygen is conveyed into ozone.

The current for the brush discharge becomes a maximum at a certain voltage, indicated by the highest point on the curve, after which there is a more rapid increase in current, and a marked lowering of the voltage is necessary in order to keep the discharge under control. The discharge then assumes the form of the high tension arc. The sparking is very pronounced and the discharge is active

Olow Discharg£

BRUSH \DI3CHAflGL

HI6H TENSION "A/fC

,Non Luminous Discharge

Low Tension Arc

Fiff. 44.

Current

Curve Showing Relation of Current and Voltage with Increasing Potential &t the

Terminals

in producing nitric oxide from the air. The fact that the voltage falls is due to the increased conductivity of the gaseous medium caused, in turn, by the higher temperature produced by the increased current. This form of arc has important technical uses which will be illustrated later.

If the current of the high tension arc is allowed to increase, a point is reached where the low tension arc is produced. This is a form of arc which has been previously considered in connection with arc lights and the arc furnace.

Production Of Ozone

Ozone is a polymerized form of oxygen. It has a molecular formula of O, instead of O, the symbol for oxygen. In other words.

Electrochemistry

a molecule has three atoms of oxygen instead of two. It has a power- ful oxidizing property which makes it highly useful for bleaching, disinfecting, oxidizing oils, etc. Its most extensive use is for water purification.

Ozone from Oxygen, Oxygen can be converted into ozone by heating to a very high temperature and then suddenly cooling, but only small yields are produced by this method. The use of the silent electric discharge at room temperatures avoids this difficulty.

Siemens-Halske Ozonizer. A great number of forms of tech nical ozonizers have been proposed. The Siemens-Halske apparatus;, indicated in Fig. 45, is an important type of commercial apparatus

Fig. 45. Section of Siemehs and Halske Ozonizer

used in water-purification plants. It consists of an iron container provided with glass windows. Passing upward through the con- tainer are a number of vertical glass cylinders coated outside with a metal which serves as one electrode. In the center of these tubes are placed the other electrodes consisting of cylinders of aluminum foil. Water is run through the container outside of the tubes to keep the apparatus cool and keep up the efficiency. The air is previously dried by means of calcium chloride or some other suitable drying agent and passes along the annular spaces between the electrodes. The metal outside of the tubes is connected to one terminal of a high alternating pressure and the inner electrodes are

Electrochemistry 79

connected to the other terminal. The iron container is connected to earth, thus preventing a risk to the operator.

A pressure of from 4000 to 7000 volts has been used on this type of ozonizer, and plants for water purification have been operated in Paris and St. Petersburg.

By placing the apparatus in a darkened room it is possible to tell from the liuninous appearance whether it is working properly. It is claimed that with an expenditure of 57 kilowatt hours, a million gallons of water may be sterilized by this means. The method of sterilization consists in compressing the ozonized air and forcing it up through towers down which the water is passing.

Fixation Of Nitrogen*

The most important use of the high tension electric arc is m the so-called fixation of atmospheric nitrogen.

Nitrogen for Fertilizers. Nitrogen is the most important element which gives value to our principal fertilizers. The increasing demand for such fertilizers and the approaching exhaustion of the great deposits of sodium nitrate and other natural nitrogen com- pounds make the problem of the future supply of great importance. The atmosphere contains a free and inexhaustible supply of this element, but in this form it is not directly useful because it is not "fixed", that is, in combination with other elements which appear to be essential for its usefulness in the growing of crops.

It has long been known that where a high tension discharge takes place, there is a partial union of the oxygen and nitrogen of the air to form the chemical compound NO.

Following the design and operation of a great many types of apparatus, it was found advisable to avoid short thick arcs and to employ long thin stable arcs which would come in contact with a large quantity of air. Units of large capacity in consuming much energy have been worked out.

Birkeland-Eyde Process. An electric furnace devised by Birke- land and Eyde has achieved a notable success in the fixation of nitrogen of the air. In this furnace a large surface of contact of air and arc is attained. The principle is illustrated in Fig. 46. Two

An exhaustive treatise on the utilisation of atmospheric nitrogen is published by the Department of Commerce and Labor under the authorship of Thomas H. Norton*

Electrochemistry

water-cooled copper electrodes are brought within a distance of one inch or less and are connected through an inductive resistance to a

Inductive Kesistancl 500\/'0Lts —

Alternator

N

Magnet Co/L-

AIR lu

Hg. 46. Diagram of the Electric Circuit in the Birkeland-Eyde Electric Furnace

source of alternating pressure of 5000 volts. The high-tension arc which is first produced quickly breaks down to a low voltage arc

carrying a heavy current. This low voltage arc is avoided by an ingenious method of placing the poles of a power- ful electromagnet at either side of the arc, Fig. 47. It is well known that a con- ductor located in a magnetic field and carrying a current tends to move out of that field. The electric arc follows this law and tends to move upward or downward, de- pending upon the direction of the current. In moving away from the straight line connecting the two ends of the electrodes, it becomes lengthened and this lengthen- ing tends to maintain the arc as a high tension arc and avoids the low tension form. In moving away and lengthening, the resistance increases, the current falls off, but the voltage increases because of the

I/VLET r

CyfS 6 AIR INLET yOKE or MAGNET

Fig. 47. Birkeland-Eyde Furnace

ao

Electrochemistry 81

lower voltage drop through the iaductive resistance. The arc is finally drawn to such a length that it breaks and a new arc is then estab- lished and goes through the same process. By using an alternating current, the arc formed by one-half of the alternating-current wave travels upward from the electrode and on the reversal of the current an arc is formed which travels downward, and these arcs are formed at the rate of fifty per second, in accordance with the frequency of the current used. On account of this high frequency it is impossible to detect each separate are and in looking into the furnace what is seen is apparently a large disk sheet of light. The air is introduced

Fit. 48. BirkeUnd-Eyde Futdaixb at Notodden

SO that it travels parallel with this disk and is, therefore, fully ex- posed to the action of the discharge.

It is estimated that the temperature of the disk is about 2300° C. The furnace is of steel, lined with fire-bricks which are perforated by holes through which the air enters.

Units of 750 kw. have been employed, such units requiring a pressure of 5000 volts. The full sized units in operation are illus- trated In Fig. 48.

Electrical Fume Precipitation

Another important application of high tension currents is in the removal of suspended particles of solid or liquid materials from

Electrochemistry

gases. It has long been known that the fine particles constituting f(, dust, and fume, may be quickly settled by pasdng between two electrodes at which a high pressure 13 maintained. There is an agglomerating effect on the suspended particles which causes them to produce larger bodies which settle by gravity. When direct pressures are employed, there is an actual attraction between the electrodes and the glomerated particles, which increases the rate of settling or collection.

Recovery of Valuable Products of Combustion. This phe- nomenon has a commercial application in the settling of valuable materials which are carried in furnace gases, not only to render these gases less objectionable to the surrounding terri- tory, but also to recover valuable materials which would otherwise be lost. It al§o looks promising in connection with the smoke problem. There are likewise innumerable instances in industrial work where the separa- tion of solid and liquid particles from the air can be advantageously effected by this method.

Cottreil Process. The commercial practicability of this action of high tension currents has been demonstrated recently in the work of Dr. Cottreil and the United States Bureau of Mines. The accompanying schematic diagram, Fig. 49, illustrates a typical pipe treater. In general it consbts of two large horizontal fines connected together by a number of small vertical pipes. Gases enter through one flue, pass through the vertical pipes and are dischaied through the other flue to a stack, exhaust fan, or other draft producer. The gas is then exhausted into the atmosphere. Some treaters are operated with an up draft, some with a down draft, according to the particular local conditions to be met.

Electrochemistry 83

Some treaters employ rectangular passages instead of pipes to connect the two flues. These are generally referred to as plate or box type treaters. The principle of operation for all these types of treaters is the same.

1,

If

The actual precipitation of the dust or fume occurs in the vertical pipes referred to above. Carefully centered in each, is suspended a small wii or a small chain. These constitute the negative electrode of the treater system. The inside surface of the pipes constitute the positive electrode. Each wire or chain is

Electrochemistry

Vie. Gl. EipeiimenUl Tubular TreMer Befon Applicstiou of Current. Fumes in the Cental

Fig, 62. Tubular Treater After Current Bus Been Turned On, SliowiDg Diisipatioa of Fiudm

Electrochemistry 85

carefully insulated from its pipe and from tlie ground, and is charged to a high potential usually at from 25,000 to 65,000 volts direct current. The tubes themselves are grounded. Thus within each pipe is created an intense electrostatic field. The gases passing through this field become ionized, and the ions travel with high velocity in a direction at right angles to the electrodes caus- ing the field. These highly charged ions are continually colliding with the suspended solid and liquid particles in the gas, and the ions impart a charge of like potential to such particles, which in turn begin to travel toward the electrode of opposite polarity. Since the negative suspended electrode is of much smaller area than the electrode formed by the inside surface of the pipe there is much greater electro- static stresses per unit ot area in the neighborhood of the wire, and as a result far greater ionization about the wire. Thus the gas receives a static charge of the same polarity as the wire, and the solid or liquid particles in the gas receive

charges of thb same polarity

which cause them to be

projected against the inner surface of the pipes, where they tend to stick and accumulate until the electric power is turned off, after which the accumulation of dust is usually collected from the pipes by loosening it by rapping the sides of the pipes and col- lecting the dust in hoppers at the bottom.

The treater tubes are usually arranged in a series of units illustrated in Fig. 50. Each unit or section is independent of the rest and is supplied with dampers and electrical disconnecting switches, so that it can be shut down for cleaning or repairs with-

86 Electrochemistry

out interfering with the operation of the other sections. The effect of turning on the current to an experimental apparatus used in connection with a copper converter is shown in Figs. 51 and 52. Direct current at 100,000 volts is usually obtained from a low-voltage alternating current by means of a specially designed step-up transformer provided with tapped windings for varying the voltage. The high-tension alternating current is then changed into a uni-directional or intermittent current by a mechanically driven rectifier which operates on the same principle as the com- mutator of a direct current generator. The disc-type rectifier, shown in Fig. 53, is generally used, except where heavy currents are rectified; then the arm-type is used.

it

'I

Si

Metallurgy

Introductory

Metal Characteristics. The metallic state in general is char- acterized by the presence of innumerable freely moving negatively charged and extraordinarily minute particles called electrons. Their presence in any substance makes it appear metallic; the remarkable facility for conducting heat and electricity, which metals possess, depends upon these same electrons; and reflecting power and opacity are correlated with their activity. Ductility, malleability, strength, and welding power also may be attributed possibly to these persistent and mobile components.

Whenever a metallic substance is dissolved in an aqueous medium, the electrons characteristically are available for the pro-' duction of an electric current, while the main atomic aggregate enters the liquid, now burdened with its residue of corresponding positive electricity. The greater the tendency thus to enter solu- tion, the more electropositive a metal is, and the more pronounced are all its other metallic properties. No two elements agree exactly in their tendency to go into solution, and, as they spread over quite a range of electrical solution potential, just as their atomic weights are spread at intervals over a considerable range, we can arrange them in an electrochemical series. Elements which faU thus to enter solution bearing a positive charge lack all metallic attributes.

Divisions of the Science. The systematic study of the science of metallurgy includes the following common divisions:

General Metallurgy, This division treats of the assembled rela- tions, properties, and processes, as derived from the detailed study of the metallurgy of iron and steel and of the nonferrous metallurgy.

Electrometallurgy y and Hydrometallurgy. These divisions treat of certain more limited fields from the electrical and wet-chemical viewpoints, respectively. Individual metals, processes, or appliances, when important enough, are commonly treated as separate sub- jects; such are: the metallurgy of steel, foundry practice, and electric furnaces.

2 Metallurgy

MetaUography, This is a strong young science which treats of the structure of the metals; it especially studies all the internal physical and chemical properties of the metallic state; it investigates metallic compounds liquid and solid metallic solutions, solidifica- tions, transitions, and crystal form.

The art of metallurgy consists in extracting the metals from their ores and in purifying and preparing them for consumption in the manufacturing industries and trades. Of course quite a bit of ore preparation often is included in metallurgy; likewise much manu- facturing may be tagged on to strictly metallurgical operations, as when a steel plant sends its product out in the shape of railroad spikes.

Extent of Metallurgical Stuidy. Metallurgy cannot confine itself to a study of the preparation and properties of the nineteen common metals-podium, magnesium, aluminum, iron, nickel, copper, zinc, pal- ladium, silver, cadmium, tin, antimony, tungsten, iridium, platinum, gold, mercury, lead, and bismuth — and of the seven common alloy- ing elements — silicon, titanium, vanadium, chromium, manganese, cobalt, and molybdenum — but finds itself in the most intimate con- tact with, and use of, many of the other phases of human activity.

Relation to Other Subjects. Mining engineering equally is con- cerned with the recovery of placer gold; the miner must dig for the metallurgist, just as the miner can afford to recover only those ores which the metallurgist can use. Ore dressing is claimed by mining engineering and by metallurgy, and is made independent only by a strong exponent. Chemical engineering in one school may embrace metallurgy, in another it may be separated fully. Electrical engi- neering finds a fertile field in metallurgical plants; civil and mechan- ical engineers often are at the same problem with the metallurgist, who as far as possible, must master their accomplishments.

The metallurgist often must do work in the strictest and purest fields of physics, chemistry, and mathematics; and their progress is the foimdation for all his best efforts. Not seldom do political economy, finance, transportation, and hygiene modify his opera- tions profoundly, but the metallurgist needs now and then to adjust his operations to the whims and traditions of those who work with him and those who buy his product.

Universal Employment of Metals. The importance of metal- lurgy is evident when we consider that the essential features of our

Metallurgy 3

modem civilization are woven on a support of iron and steel; remove this metallic skeleton or imagine it lost, and our personal sphere utterly collapses.

Hardly an effort of labor can be performed without the use of a metallic object, be it the work of the laborer in the ditch with his iron-carbon alloy, or the President signing a state document with a platinum-iridium pointed gold pen. We live in homes well equipped and decorated with metallic objects; we carry metallic objects for use and show — the same as fabrics — and consider a gem perfect only in the most costly setting.

Relative Production of Metals. General. The transportation of ores is the greatest tonnage commodity of the railroads. The strictly metallurgical industries rank well to the front — as far as the money value of our yearly products is concerned, over a billion dollars' worth of metal in the mifabricated state being produced each year. The stock of accumulated metals is one of the chief treasures and resources of any people.

Gold. Gold is the standard of value and the basis of finance. While our national wealth, both private and public, is increasing enormously year by year, our gold production is not quite a dollar's worth per person at the present time. For over 100,000,000 people, the United States produced slightly under $99,000,000 in gold during 1915.* As a matter of fact, the world's production of gold now is on the decline. Trade exigencies swing the transfer of gold violently from nation to nation. One year we export more than we mine; another, the whole world's production of some $450,000,000 is shipped to us. Financial panics are largely scrambles for gold. Gold has slight intrinsic value and any rational substitution of a new material for it or of a fiat basis for values, immediately would have the most profound and sweeping reaction, not only on gold mining, but on the entire number of industries connected with the production of silver, copper, and lead.

Other Metals. During 1916 there were produced, per capita, in the United States over 950 pounds of iron, 24 pounds of copper, 1 1 pounds of lead, 12 pounds of zinc,, and 1 J pounds of aluminum. We are, by far, the leading nation in the production and use of the metals. There are strong indications that more populous nations than our own gradually will find need for the metals, as we do. There is,

4 Metallurgy

therefore, little likelihood of any very long continued slump in either metal production or metal values.

Future Progress. Matters of the greatest import are the progress continually being made in the production of purer and purer *metals in huge quantities, and the striking success in making alloys of new properties. There is no reason to think otherwise than that this phase of metallurgy is still in its beginning; a conception prom- ising to everybody.

Literature on MetaUurg;y. The bulletins of professional, scien- tific, and government bodies afford an abundance of first-class information on all current metallurgical subjects. The trade jour- nals get some new articles, but mainly spread the more technical information of the first group. Perfunctory treatises demand such attainment by their authors that, if they are at all broad in scope, they fail lamentably. Treatises on special subjects, on the contrary, are usually very much worth while. In general, both the science and the industry are presented exceptionally well to the public.

References. The information contained in the following treat- ises and periodicals is of the first quality. General Metallurgy:

"Introduction to Metallurgy", Roberts. Austen (1910)

"Principles of Metallurgy", Fulton (1910)

"Metallurgical Calculations", Richards (1907)

"Physical Metallurgy". Rosenhain (1914)

"General Metallurgy", Hofman (1913)

"Metallographie", Guertler (1912-1913)

"Revue de M€tallurgie" (monthly), Paris

"Metallurgical and Chemical Engineering" (semimonthly). New York

"Metall und Erz" (monthly), Halle

"Bulletin, American Institute of Mining Engineers" (monthly). New York - "The Mineral Industry" (yearly), New York Iron and Steel:

'Cast Iron in the Light of Recent Research", W. H. Hatfield (1912)

The Metallurgy of Steel", Harbord and Hall (1911)

Xiquid Steel", D. Carnegie (1913)

(d

€<r

Metallurgy 5

"]

"] "]

Metallography and Heat Treatment of Iron and Steel' Sauveur (1916)

'Metallography of Steel and Cast Iron", Howe (1916) 'Cementation of Iron and Steel", Giolitti (1914) 'Stahl and Eisen" (weekly), Duesseldorf 'The Iron Age" (weekly). New York 'The Iron Trade Review" (weekly), Cleveland Copper:

'Metallurgy of Copper", Hofman (1914) Tractiee of Copper Smelting", Peters (1911) 'Hydrometallurgy of Copper", Greenawalt (1912) Lead:

'The Metallurgy of Lead", Collins (1910) Zinc:

"Zink und Cadmium", Liebig (1913)

General Metallurgy

Properties Of Metals

Reducibility. The useful metals cover almost the entire range of the metallic elements in the electrochemical series. This gener- alization of the chemist is the same as the metallurgist's statement that the metals have all degrees of reducibility. The sequel illus- trates abundantly what we mean. Sodium stands near the very extreme of the electropositive end of the list, with an affinity for oxygen and chlorine so powerful that decomposition and isolation are effected only by the most energetic chemical or electrochemical means. At the other end of the series are gold, iridium, and plati- num, with solution pressures so faint that they naturally retain the metallic state and can be forced to combine with only a limited number of the most electronegative nonmetallic elements. Simply heating any of their compounds throws out these latter metals ready to melt for the market.

Metallurgical Series, The metals, in general, are won by heat- ing and reducing under proper chemical influences, but there are important exceptions. The arrangement in metallurgical series, Table I, indicates the degree of reducibility of the various metala

Metallurgy

TABLE I Comparative Reducibility

Dkgrbe of Facility

Means

Mbtal

(1)

By heating compounds — if originally metallic, merely fuse

Gold Platinum Palladium Iridium

(2)

From oxide compounds, eatily, by metalhc iron or by hot carbon monoxide

Lead

Cadmium

Tin,

Bispauthj

Copper

Merdury

Silver

Antimony

(3)

Only by carbon at 1000** C, in absence of car- bon dioxide

Zinc Iron Nickel Cobalt

(4)

With carbon in the electric furnace, or with metallic aluminum also acting at extremely high temperature;

Chromium

Manganese

Titanium

Vanadium

Molybdenum

(5)

Only by electricity, in absence of free or unavail- able electronegative elements

Sodium

Magnesium

Aluminum

Crystallization. One of the superlative properties of all metals is crystallization, and on the exact condition of the crystals in any metal often hangs every degree of usefulness. An intimate glimpse into the complex nature of an ordinary steel is given in Fig, 1, in which the sharply separated crystals with boundary cement and internal granules are as plain as the stones in a building. The same applies to a sample of ordinary copper as seen in Fig. 2.

AH naetals have been found to crystallize on solidifying -from the molten state; even after the severest strains and deformations, the crystal nature persists. Deformed crystals give birth to a new growth of crystals, if the temperature will allow the readjustment. Maximum ductility usually accompanies well-grown crystals; maxi- mum, strength accompanies the first incipient growths of a newly disseminated structure from some previous formation, probably through surface forces. Brittleness and weakness commonly are developed through the coalescence between large crystals of the

Metallurgy 7

material by some substances of friable nature; impuritres and over- heating thus form an aggravating combination.

An amorphous state is a plausible assumption to account for the cement between grains, the debris along slipped cleavage planes and colloidal metal solidified by pressure instead of fusion. The study of this condition is now assuming notice and promises brilliant results for science and industry.

Hardness. The hardness of a metal often is of prime importance. The ideas of scratching, cutting, indentation, transient impact, and

FIS.l. VeiTLowCu-boneteel. SpadmenMac- Fls. 2. Rolled and Annealed Copper. Bped-

lufied;tnDiBDieten;SbDW3 theCDuea men MainiBed 1000 DUmeten; Shows

Grain and Secondary Gianulationa Coarse Oiaia and fibers ot tba Ortun

permanent deformation all are conveyed in the term hardness. Various measuring instruments have been devised; of these the Brinell ball- indentation machine and the Shore scleroscope are the most common.

BrineU Hardness Tester. In using the Brinell machine which is shown in Fig. 3, the steel ball, 10 mm. in diameter, is pressed into the metal with a force of 3000 kg. The size of the indentation after applying the pressure for 15 seconds measures the hardness.

Scleroscojie. As illustrated in Fig. 4, thb instrument, operated pneumatically, lets fall a weight whose diamond pomt cuts the

8 Metallurgy

surface of the metal, yet is blunt enough to be quickly resisted by the spreading metal; the upward rebound is measured on a scale whose 100 mark b exactly equaled on a hard standard steel.

Strei;th. Factors. This property of resistance to pulling apart or bending is modified wonderfully both by the chemical nature of the particles of a metal, by their size, and by the way in which they are arranged. The purest and softest iron which has a

;. S. ErineU Hardnt

tensile strength of some 40,000 pounds per square inch, can be brought, by alloying and working and right heating, up to a strength of 400,000 pounds per square inch in small sections. The proper heat treatment and working often can increase a metal's strength 100 per cent over an original cast condition.

The strengths of all metals vary so with composition and treat- ment that any specified strength has little meaning unless accom- panied by the facts of composition, and of heat and mechanical treatments.

. Metallurgy- 9

Fatigue. All metals are susceptible to a gradual weakening by progressive internal rupture, when subjected to enough alternating strains to affect — although to not exceed — the elastic limit of the metal. This is called fatigue; many materials yield to it after a few thousand trials; those which require millions of alternations to rupture are said to be very resistant to fatigue.

Fig. 4. Sbore Sdeioscupe Testioe Baidnera of Csrlriilce Cua

Ctrariny oS Shore Insirumeni and Marmfactvrino Company.

New York City

Plasticity. Plasticity, or the flow of metals under pressure, is by no means a general or uniform property of the metals. As already intimated, there are all degrees of malleability in the cold, the degree evidently being associated closely with the perfection of electrical and heat conductivities (see Table II). What may be considered malleability at one temperature is the slipping of the atoms along crystal cleavage planes; at a higher temperature, a similar deforma-

Metallurgy

Table Ii

Physical Constants

Mbtal

Mbltimg

Point

(Degree

centigrade)

COBmCIBNl or LiMBAB

Expansion

(Per degree

between

100")

Dbnbitt

(Water - 1.0)

Spbcific Hbat

(Water - VO)

El.Bctbical

Conduo- Tivitt At

(Hg.- 10,650)

Constant of Hbat Con- duotivitt (Calories per second tnroogh 1 cen- timeter cube;

1 degree diflference)

Sodium

Magnesium

Aluminum

Iron

Nickel

Copper

Zinc

Palladium

Silver

Cadmium

Tin

Antimony

Tungsten

Iridium

Platinum

Gold

Mercury

Lead

Bismuth

, 320.9

211,000 230,000 324,000 131,000 144,200 620,000 186,000

679,'666

144,100

76,600

27,100

63,566

461,000

10,630

50,400

9,260

tion may be the flow of an extremely viscid and tenacious solid solution.

Conditions. Although this malleability is a cardinal property of the most useful metals, each metal or alloy requires specific con- ditions for making use of the property, if, indeed, it can be used at all. For cold working, a metal frequently is annealed, lest crystal ruptures be developed exactly as in an overdone fatigue test (rolling gold and silver). Compounds present dare not be overlooked (cementite present in tool steel in the cold is in solution at red heat). Temperatures and chemical actions must be within bounds (steel "burned" has been heated until actually deeply oxidized), while, finally, at the temperature of optimum workability, extreme care must be taken not to damage physically the weakened but still cohesive metal (in welding steel, slag and scale often are forced into the main body of the metal). In fact, the conditions under which each separate metal shall be worked, must be most carefully studiied.

Metallurgy

TABLE III Chemical Source of the Metals

Native

Oxides

Sulphides

Cabbonates

Silicates

Chlobidbs

Copper Paliadium

Aluminum

Nickel

Magnesium

Copper

Sodium

Silicon

Cobalt

Iron

Zinc

Magnesium

Silver

Chromium

Copper

Copper

Silver

Gold

Manganese

Zinc

Zinc

Mercury

Iron

Lead

Lead

Iridium

Vanadium

Silver

Platinum

Titanium

Molybdenum

Bismuth

Copper Tin

Cadmium Antimony Bismuth

Ores

Economic Value. An ore is a metal-bearing substance from which a metal, alloy, or metallic compomid can be extracted at a profit. Ores are the aggregates containing the minerals of economic value. Gangue is the portion of the ore not desired or which must be wasted in the recovery of the metal. Gangue removed by a fusion is called slag. The gangue of one century or decade is not infrequently the ore of the succeeding period.

The economically valuable minerals are chiefly native metals, oxides, sulphides, carbonates, silicates, or chlorides, as grouped in Table III.

Distinctions in Values. It is vitally important to distinguish an ore deposit from an occurrence of a few handsome mineral speci- mens. The universally distributed and often pure and massive sulphides of iron are never directly ores of iron; the stupendous amounts of fairly pure silicate of almninum are not ores of aluminum; dolomite is not an ore of magnesium; sea water, although it may contain more gold than does a gravel which is actually worked, yet is not an ore of gold; strictly speaking, we have no ores of cadmium, palladium, or iridium, for these metals are recovered only as by-products in the working-up of other metals.

Again, we must keep in mind that, although the metallic con- tent of a rock figured into dollars at market metal prices may amount to $50 or $75 a ton, yet that rock may be without value, either if the metals are inseparable, or some inconspicuous deleterious element is present, or if the cost of treatment is greater than the recovered values.

Metallurgy

Metallurgy 13

Sampling

Importance. All modem metallurgical operations are uiuier chemical control. Before a chemical analysis can be made, the material must be sampled properly. Obviously, then, accurate sampling is equally important with correct analysis.

The sampling of materials is found in all stages of metallurgical operations, from raw material to finished product. It is essential from the buying and selling viewpoint, for economy and recovery, for purity and composition of final product.

Methods. Sampling may be accomplished in the mine. There it will be done by sinking shafts, by churn drilling, by core drillmg.

by twist drilling, by exposure cuttings, by grab sampling, or by selecting certain units such as a small car-full or an entire load in a railroad car.

Sampling Mill. Many mines and metallurgical plants main- tMn special mills in which systematic sampling is etfected by scien- tific divisions after finer and finer crushings. If the material is already fine, a fKirtion will be selected by coning and quartering, by fifth-shovel sampling, or by the use of stationary cutters. If the material is coarse and needs to be kept so, the sampling will be by selecting portions from a falling stream, crushing, and again cutting the stream. In this way, after four to six selections, a small sample is obtained which accurately represents the entire lot of many tons.

14 Metallurgy

Fig. 5 gives, in outline, the operation of such a mill. The student should follow in detail the course of the material from the in-coming to the out-loading car. Note how many times the ore stream is divided before the sample finally is received in the safe. Observe the methods for reducing the size of the chunks.

The actual sampling cutter in this mill is seen in Fig. 6 just as it is placed in the mill. The single collecting hopper A guides the ore stream through the narrower channel B to above the fraction- ating oscillator D, which separates it partly into the discard spout E, and partly into the sample spout F. f? is the oscillating shaft; K an eccentric gear; / a gear shift.

Laboratory Sampler. Fig. 7 illustrates a simple mechanism to effect the cutting-out of a sample on a much smaller scale. It is seen that the feeding spout has mechanical shak- ing to work the material in uniformly. The discard b cleared away on the belt conveyor, while the selected smaller sample is caught in

main chamber is a revolving segmented cutter which throwa a large portion of the ore stream out through the large discharge, and throws a smaller but impartially selected portion into the funnel over the bucket.

Crushing and Cutting. In the crush-and-cut method of mill sampling three very distinct ratios have to be maintained properly. These are: (1) size of largest particle to total weight of lot, with an ample factor to allow for increasing in homogeneity; (2) number of selections to uniformity of the lot — the more dissimilar, the more cuts are required; (3) size of opening to size of largest particle — which properly may be about 10.

Fig. 8 pictures one of the most convenient laboratory cutters yet deagned for fine dry materials. When material is poured into the

Metallurgy 15

hopper with a shaking motion, it will receive numerous cuts and be divided into two portions. The cutting then can be repeated until the sample selected is of small enough size.

Coning and Quartering. Where mechanical methods are not available, excellent results can be obtained by coning and quartering. This venerable method is discredited abundantly but is wonderfully serviceable when necessity demands.

In Fig. 9 is shown this practice in a large Mexican smeltery. One by one the piles will be spread out, until they are not over 10 or 12 inches thick; with a marker the lot then will be quartered, and

men will shovel away opposite quarters as discard and again cone up the two remaining quarters. This will be continued, with much breaking of the lumps, until the sample is small enough to go to ike laboratory for grinding and for further division on a cutter like that of Fig. 8. In the illustration the Mexicans in the background are at work shoveling the discarded quarters into the wheelbarrow. Such a sampling floor is kept scrupulously clean; the dust is kept down with sprinkling.

Molten Dipping. Well-mixed molten materials are sampled accurately by dipping out small units, each approximately of the right size for the chemist or assayer without further divblon.

Punching. Punch sampling of cakes, slabs, and ingots is much used. We have learned that all metals crystallize on cooling to

16 Metallurgy

assume the solid state; this means that the mother magma will be em'iched with impurities and solidify last; in other words, all ingots show segregation. Sometimes the irregularities can be kept small; often they are surprbingly large.

Testing Finished Product. Sampling a finished product by selecting and testing a few imits is practiced commonly. Obviously

ng. 9. Sampling, Floor ot a Mosican Smeltery

thb presupposes a uniform product; such sampling has the same inconclusiveness as there is in the case ot grab sampling.

Pretreatment Of Ores

Metalluiical Processes in Ore Dressing. Besides the numer- ous and highly technical methods of ore concentration as practiced in the art of ore dressing, there are a few processes distinctively metallurgical which must be considered.

Drying. Not infrequently materials must be dried to avoid freight charges, or in order to supply perfectly dry material for further treatment (as preparatory to electrostatic separation), or preparatory to roasting. Mechanical dryers have been brought to high perfection and can do the work efficiently. Such a revolving tumbling and heating cylinder is seen in Fig. 10. Both the fire box and the flue are at the far end, for m this particular type the gasea

Metallurgy 17

of combustion travel twice tlie length of the cylinder before discharg- ing; it has internal partitions for this purpose. The feed hopper is ' at the far end, and the material discharges from the near end into the rolls.

Calcining. Calcining in kilns or furnaces may be practiced to get rid of mobture and carbon dioxide preparatory to the shipment of ores, or to put the ores in the best form for reducrion. Several types of furnace are used.

Roasting. Boasting may be performed to get rid of sulphur, to change from sulphide to oxide, to change to sulphate, to rid of

arsenic, antimony, or tellurium, with salt to chloridize, or simply to volatilize. The most conservative method is on a flat-hearthed reverberatory; many more recent and improved types are in use. Fig. 11 shows the hand-rabbled reverberatory as used in many countries and for all of the purposes just mentioned. The charge will be pushed slowly the entire length of the furnace, toward the fire box, and finally raked out as we see the man doing in the picture. Sintering, Sintering is becoming more common with iron ores as preparatory to blast-furnace reduction; if carried out in a revolv-

10B

Metallurgy

Metallurgy

ing cylinder it likely will be termed nodvlm-ng. Fig. 12 shows just such a Dodulizing cylinder. The ore is fed in through the opening A; B is the cylindrical steel drum revolving on rollers C; the dis-

i>— DiKhwgB Hood; fi— Gi

charge hood is at Z*; the gas burner is at E; and the gases exhaust through the stack F.

Roast-Sintering. This is now the standard preparatory method for sulphide ores before smelting in the lead blast furnace. It leaves the material both desulphurized and chunky. When iron ores are

Fig. 13. Continuoua Roost-anti

thus treated, the sulphur is lowered and the material is agglomerated as well. The principle of the continuous machine with down draft is seen sketched in Fig. 13. The charge feeds down through the

20 Metallurgy

mixer and the moistener upon the continuous-grate system just in front of the ignition burner. When ignited, the glowing cake is carried across and over the suction box as the combustion extends through the mass, so as to complete the work, before the cake breaks off, finished, into the waiting car.

Briquetting. Fig. 14 shows a pug mill in the background, within which two heavy rollers mix and grind the charge and finally press it through holes in a revolving thick steel disc so as to form the round cakes which are seen piled beside the conveyor extending forward from the pug mill. These particular cakea

have been ground up with milk of lime as binder: This process is common for making fine and powdery materials into cakes suitable for blast-furnace reduction. Because of the rapid devel- opment of roast-sintering as a preparatory process, briquettes are fast losing in importance.

Chemical Soluticm or Fuaion. The method of chemical solution or fusion is sometimes found necessary in cases where other and cheaper methods are not suitable. The process requires no unusual apparatus. Pure alumina is prepared thus from bauxite; by this process tungsten can be separated from the iron and the lune with which it occurs in nature.

Metallurgy 21

Furnaces

Classification. A bewildering variety of furnaces is in use in the metallurgical industries. Almost every metal as well as each process for the same metal has its own particular furnace. Only in the broadest sense can furnaces be classified. They cover a great range of working temperatures of capacities from ounces to thou- sands of tons, and of chemical influences from the strongest oxidizing to the most powerfully reducing. Classification according to fuel and mode of receiving the heat is as follows:

I. Fuel Furnaces (either gas, oil-, wood-, coaU, or coke-fired):

(A) Direct Contact with Solid Fuel

(1) Hearths

(a) Open hearths or crucibles (blowpipe melting)

(b) Forges (the ancient Catlan forge for making iron)

(c) Lead-ore hearth (for melting rich galenas)

(2) Shaft furnaces: Blast furnaces. Used with solid fuel for reducing ores of iron, copper, lead, and tin

(B) Charge Separated from Fuel (either solid, liquid, or gas fuel); radiation heating mainly

(1) Reverberatory furnaces. This type of furnace is used for more purposes and on more metals than any other sort of furnace; variations are equally numerous

(C) Charge Inclosed; heated by conduction through walls

(1) Crucible furnaces (for melting steel, etc.)

(2) Retort furnaces (for smelting zinc, etc.)

(3) Tube furnaces (for liquating bismuth)

(4) Muffle furnaces (for roasting sulphides and the rich sulphur-dioxide gas used to make sulphuric acid)

II. Charge Containing Own Fuel:

(A) Converters (for blowing matte to blister copper, and iron to steel)

(B) Aluminothermic Crucibles; in which oxides are reduced to metals with metallic aluminum

HI. Electric Furnaces:

(A) Pure Arc Heating (Stassano steel furnace)

(B) Induction (Roechling-Rodenhauser type)

(C) Resistance (aluminum furnaces)

(D) Arc and Resistance, Combined (Heroult and Girod).

22 Metallurgy

Variation cf Types. Electric furnaces, converters, crucible furnaces, and reverberatoriea are made tilting as well as stationary. Almost any combination of the above furnaces is possible and many such are in use.

Insulating Materials and Refractory Linings. What substance shall restrain and hold the reacting chemicals in the multitude of

furnaces just described? What materials will keep the heat in? What materials will conduct the heat away fast enough? What will withstand very high temperatures? What will resist excess of acid influence? Wliat will resist hot and powerful bases? No subject is more important to the metallurgist than refractories, for

Metallurgy 23

possibly it is not only high temperatures and chemical action but changing temperature vrhich must be withstood.

(1) Chilled Substance Itself. This is a very neat and absolute solution when it can be applied. It is used most in the electro-thermic f'ornaces but borders on our next refractory, water-cooled jackets.

(2) Water-Cooled Metal Jackets. Here a very thin layer of the charge will be frozen on the metal which is cooled by an abun- dant supply of water. All blast furnaces now are cooled with water blocks or large flat or annular jackets about the fusion zone. Fig. 15 shows a large rectangular jacket assembled in the shop. Hand holes for cleaning out are at the very base; tuyere thimbles are in each jacket just below the bosh; about the center of the bosh are the water inlets; the overflow is at the very tip top of each jacket. The jackets are firmly bolted together to keep from being squeezed apart by the charge.

(3) Fireclay, Hydrous aluminum silicate, as found abundantly in nature, not only lends itself well to molding and baking into strong shapes, but admirably resists temperatures up to some 1500° C, and is neither decidedly acid nor basic in its character. This is a very widely used refractory.

(4) Silica and Siliceous Materials. This refractory also is easily worked and fritted into suitable shapes. It is used much for acid hearth linings, for roofs, and for side walls.

(5) Carbon and Graphite. The crucible of the iron blast furnace is essentially a graphite-lined receptacle, and is automat- ically so. This refractory will stand any obtainable temperature, but cannot be used in the presence of air or reducible oxides.

(6) Magnesium Oxide. Magnesium oxide, which has been carefully calcined and shrunk, is a widely used brick and hearth lining. It is for use with the bath basic or metallic. Particular care must be taken that steam does not get a chance at any time to slack and ruin this material.

(7) Bauxite (AI2O3).

(8) Carborundum (CSi).

(9) Chromite(FeCT20A). '

(10) Brasqu£ (mixture of sand, fireclay, and coke).

(11) Zirconia (Zr02).

(12) Boron Nitride (BN).

Metallurgy

Brasqtie is an ancient refractory, now little used for more than backing some primary lining. The others of the last six are all promising materials which doubtless will receive greater application when they become better known and more available.

Metallurgy Of Iron And Steel

Ores Of Iron

t

Ps

Supply and Consumption. Although the world is using up iron ores at the rate of over 150,000,000 tons a year, the supply keeps increasing from new discoveries and better preparation of lean ores. The principal countries of the globe are well supplied, each with enough in sight to last many years. The United States is especially well provided, not only within its own borders but in adjacent coun- tries. We now have probably 10,000,000,000 tons which we may call the reserve, and our present yearly consumption of some 50,000,000 tons can be increased considerably without fear of exhaustion.

Mineral Sources, The minerals which constitute the main ores of iron are shown in Table IV. Magnetite and siderite are minerals forming only minor ore deposits as at present available. Hematite is our present chief mineral. The deposits of the hydrous oxides are especially large and have more promise for future usefulness.

, Methods of Preparation. In preparing iron ores for the blast furnace we use drying, washing, and magnetic concentration, cal- cining, nodulizing, sintering, and briquetting.

Fig. 16 indicates with what seriousness the large companies are beginning to work lower-grade deposits. This particular plant is for washing some 20,000 tons of iron ore each day. It is a carefully designed and costly plant. The fines which are blown out of the

TABLE IV Principal Iron Ores

MlNSRAL

Composition

Iron, Percsntagb

Magnetite Hematite Limonite Goethite Turgite Siderite

FeaO,

2Fe203. 3H,0 FeOg. H.O

2Fe.,0,. HP FeCOa

' 72.4

Metallurgy 25

furnace and collected in dust catchers and washers are just as good as new ore, if they are agglomerated; the working up of these fines with fresh fine ore is a rapidly developing phase of the smelting.

Blast Furnace

Importance. The blast furnace is the real heart of the iron and

ateel industry; it is the most important device which mankind yet

has developed. The continued operation of the furnaces is related

to our daily life in a similar sense as is the daily rising of the sun —

Fig. 16. IroD-Ore Wtuhins PI Tbb plant ialoa

we could get along without either for a while, but soon our whole condition of existence would change.

Plao of Operation. The blast furnace for smelting iron ores is one of our largest machines and also one of the most complicated. At the top is charged in the iron ore, the limestone to flux the gangue, and the coke as the fuel. Near the top exit continuously the gases from the combustions and reactions, as well as the flue dust. The gas has considerable fuel value and is used partly to reheat the blast and partly to drive the engines for furnishing the blast, while a fur- ther portion is left over to use as desired in the plant. Through the tuyeres near the bottom of the furnace a great quantity of hot air is

26 Metallurgy

blown in to bum the coke and to maintain the smelting tempera- ture of some 1600° C. Iron is tapped out every six hours from the bottom of the furnace, and slag is tapped more frequently from the cinder notch a little higher up but still below the tuyeres. As the charge settles through the furnace the iron ore is reduced to

Fig. 17. Vertical Section o( Iron Blast Furnsce

Cvwie'v of "Bugineiring and Alining Journal"

metallic iron. The limestone is calcined to lime; when the charge has settled far enough, the lime and silica of the gangue combine to make the 'slag, while the iron saturates with all of the available carbon, silicon, manganese, and phosphorus, and at last, wholly molten, trickles into the crucible to await casting time.

Metallurgy 27

Elements of Construction. To accomplish the reduction fully antf to maintain the high and constant heat necessary, a large and immensely strong furnace is required. The base b a massive foun- dation; the crucible is water-cooled and is bound in with thick steel bands; the tuyere nozzles are clamped solidly; the boshed fusion

zone is of the best firebrick held with heavy thick steel bands and is cooled thoroughly with bronze water blocks; the shaft is a massive steel shell lined with first-quality firebrick.

Fig. 17 is a section through a large iron blast furnace. This cut admits of a close inspection of the lines of the furnace: the cm-

28 Metallurgy

cible, tuyfereS, and boshed zone each are indicated clearly. Above the boshfed zone the main upright truncated cone of the shaft extends upward; note how this shaft is supported on special columns, and see the thickness of the walls. Figure out how the bell mechanism at the top allows the charge to get inside thei furnace without letting the gases escape. The inside dimensions should be copied and the shape should be redrawn on a larger scale. Follow the iron ore from the ore bin, and explain which part comes out through the dust catcher, which part through the iron tap, and which part through the cinder notch.

Actual Operation. In the halftone from the photograph of the furnace. Fig. 18, we have a fair view of what the inside of the casting room looks like when the pig iron is running from the furnace. The hot metal is pouring out in a thick stream and runs through the iron and sand channels into the ladle at one side and lower than the floor of the casting room. Men are on hand to keep the flow of metal clear of obstructions. The big bustle pipe around the bosh is much in evidence, as are also the pipes connecting to the tuyeres which are seen inserted between the steel bands around the furnace. Just over the runway, which is immediately above the bustle pipe, can be seen the many overflows of the cooling water which has circulated throughout all the lower section of the furnace inside the cooling blocks; each of these overflows is in plain sight from the floor. A big annular drain box collects all the water, which then flows away through the big pipe leading down over the men at the right.

The usual furnace of today makes about 500 tons of pig iron a day. Each ton of iron produced requires some 2 tons of ore and a ton of coke in the charge, besides the necessary limestone, while for this same tonnage of iron some 4 tons of hot air must be driven through the tuyeres under a pressure of from 15 to 30 pounds per square inch. At the top a double bell-valve arrangement is neces- sary to drop in the frequently arriving skips of charge without letting out the gases which are carefully conserved and, after leading down and through the dust catcher, are conducted to the other parts of the plant.

Secondary Elements Of Furnace Plant

While the blast furnace is the most vital part of any iron or steel plant, there are accessories absolutely essential for its operations.

Metallurgy 29

Raw Material. Enormous stocks of ore, limestone, and coke must be ever ready for charging into the insatiable stack; this means great piles of ore and stone, and plenty of coke either being made or continuously coming into the plant. Reliable and powerful bridges, cranes, grab buckets, transfer and scale cars, etc., must be in place to span the stock piles and to load the skips.

Stoves. Huge stoves are built in line near the furnace to heat the blast; four stoves, each nearly as big around and as tall as the furnace itself, are commonly supplied to heat the blast. The stoves

Fif. 19. Eiterlor View of Put oi a Blut-Funuce Pluit

are thick steel shells with firebrick linings and checkerwork fillings. Through one hot unit the blast always will be passing on its way from the engines to the furnace, while the others will he heating ready to take their turn at half-hour intervals.

Power Plant In a building near the furnaces powerful engines will be at work compressing the air to go to the furnaces. These engines may be steam driven by means of boilers heated with the furnace gas; they may be gas engines driven by the furnace gas burned internally; they may be turbine engines driven by steam from gas-heated boilers. In any case, the power plant is a very important part of the plant.

30 Metallurgy

Pig Casting. Fig. 19 indicates clearly enough the furnace sticking up through its casting room on the right of the picture. The gas is led from the top of the furnace through the downcomers and dust collectors across to the line of stoves and the boiler house (both in center of the picture). The power plant is the larger building on the left and behind this is the water tower for the plant supply. At the very left edge is the location of the casting machin- ery; the hot pig iron has to be switched over to this building in the big ladles before it is cast into pigs.

The molten iron is tapped out of the furnace and runs into ladles to go to either the steel plant or the casting machine. In the steel plant the iron probably will be poured into a large receiver and from there will be taken, still molten, to the steel furnaces. Iron to be used in trade or stored for future use is cast in molds which are strung together, conveyor fashion, so as to give continu- ous service. These ingots of iron, or pijs as they are called, fall from the casting conveyor on to Cat cars for storage or transporta- tion. An older method of casting was to run the metal out into closely packed sand molds; it is little used today. For further handling of the pigs, cranes with an electromagnet for tackle are employed.

Constitution Of Iron Compositicn Of Piq Iron

- Elements Present. Having studied the powerful reducing condition inside the iron blast furnace, it is no surprise to us to know that any other element present in the ore and as easily reduced as iron will come out with it as it runs from the furnace. The well- known exception to this rule is that sulphur can be fluxed off with the slag, if the slag is mahitained both highly fluid and rich in lime. But the reduction goes even further than this, for, in the presence of the metallic iron, elements, not reducible otherwise, are quickly absorbed and kept from reverting back to oxide.

Thus it results that all pig iron contains more or less of silicon, manganese, phosphorus, sulphur, and small quantities of any other reducible element originally present in the ore or in the charge — these may be chromium, copper, arsenic, titanium, vanadium, etc. The iron, of course, is saturated with carbon nearly all of which

Metallurgy

TABLE V Variation of Combining Elements in Pig Iron

Usage

fNo. 1

Foundry No. 2

Irons jNo. 3

INo. 4 Forge

Bessemer-acid Bessemer-basic Open-hearth-acid Open-hearth-basic I'erromanganesel Ferromanganese S]Diegeleisen Ferros'liconl Ferrosiliconj Silico-Spiegel

Silicon

Sulphur

Phosphorus

Manganese

Under .10

Under 1.0

Under .10

Under .05

Under 05

Under l.b

Under .03

Under 1.0

Under ,03

Under 1.0

Under .05

Under .15

15.0-30.0

Under 07

Under .02

Under .08

Under .01

Under .15

15.0-20.0

Carbon

Under .40

will separate as graphite if it cools slowly enough, and otherwise will be in combination and make the iron white.

Physical Properties. Now, the physical properties of the material made by remelting and recasting pig iron (then called cast iron) will depend largely on whether the carbon is grapliitic or com- bined in the final casting. It will fit the use for which it is intended* only if it has the right amount of graphite and the right amoimt of combined carbon. The size of the graphite flakes also is important. Much manganese makes the iron hard; much phosphorus makes it brittle; much sulphur makes it quite unfitted for many purposes. But the effect of each of these constituents is not only directly but indirectly through simultaneous effect on the state of the carbon. Iron of something like the compositions shown in Table V will be made for the purposes indicated.* The limits are rather wide, and, for many purposes, the right composition will be obtained by mixing irons in varying proportions.

Iron And Carbon

Various Proportions. Ferrite. The scientific name of pure iron is ferrite which melts at 1530° C. On heating pure iron, it loses its magnetism at 768 degrees and changes its entire crystalline nature at 909 degrees; the exact converse takes place at about th

From Stoughton, "Metallurgy of Iron and Steel".

32 Metallurgy

same temperatures on cooling. The three forms of f errite are known as alpha, beta, and gamma f errite.

Ferrite is f omid in commerce as dead-soft steely ingot iron, and electrolytic iron. It is impure with slag inclosures in wrought iron, and is impure with amorphous carbon separated and some silicon in solution in malleable iron.

Eviectic Point. Adding carbon to molten iron lowers the melt- ing point until 4.3 per cent of carbon is present, when still more carbon raises the melting point even more sharply. Melts having less than 4.3 per cent of carbon freeze out a solid solution of carbon dissolved in iron which we call austenite. Melts holding more than 4.3 per cent of carbon freeze out carbides, the most important of which is FcsC. This carbide occurs frequently in high-carbon materials. The melt containing exactly 4.3 per cent of carbon, which freezes at 1135 degrees, is a mixture of 47.7 per cent of austenite — austenite being a solid solution of carbon or of iron carbide in iron — and of 52.3 per cent of cementite, and is called the eiUectic because of having the lowest solidifying temperature of all the pos- sible mixtures in various proportions of iron and carbon, namely, that with 4.3 per cent carbon content.

Pearlite. As indicated by the diagram. Fig. 20, austenite is stable at high temperatures only. In alloys with less than 1.7 per cent of carbon, the austenite, on sufficient cooling, separates out ferrite along a definite line, if there was less than 0.85 per cent of carbon in the solid solution; and carbide is separated out, if there was more than 0.85 per cent of carbon in the solid solution. Here, again, a minimum point is found at 0.85 per cent of carbon and 723° C. The mixture separating is called the eutedoid, or, more commonly, pearlite, because of its play of bright colors. It has 88 per cent of ferrite and 12 per cent of cementite.

Other Gradations. With the alloys of more than 1.7 per cent of carbon, austenite and cementite may decompose into ferrite and graphite, if held until equilibrium is established at high enough temperature — above 700® C. But depending largely on the rate of cooling, we may get all gradations between austenite and cementite mixtures, and between ferrite and graphite mixtures. Manganese, silicon, and phosphorus influence the tendency to separate graphite in strong degree.

Metallurgy

We may, then, by adjustments of chemical composition and the rate of cooling, get an immense variety of materials in the cooled

eioo'

JJusienitff I euteetic and OamnHU

vwor

woo*

FhrrCt and raphitm - StabU

Ferrite, ligarUte and Craphitc nstable Brar-lit CYmentile and Craphit

4J% 6 T

Percent Carbon

Fig. 20. Iron Carbon Equilibrium Diagram

—Hi

to

iron at will. The art is known as founding. Foundry practice now is based on well-established science and is making rapid progress.

M Metallurgy

In composition the cast irons group about the eutectic mixture; likewise, the steels group about the eutectoid mixture. The dia- gram in Fig. 20 represents one of the greatest condensations of empirical knowledge yet accomplished in the realm of metallurgy. It can be criticized in many respects, and will be elaborated and perfected further; just as it stands, however, it can be used to enor- mous advantage by anybody concerned practically in the metal- lurgy of iron and steel.

Foundry Practice

Field of Operations. The great industry which annually melts som 6,000,000 tons of iron into a bewildering variety of objects, large and small, hard and soft, some for strength and some for beauty, is all too diversified for summarizing.

Foundry practice includes the blowing of pig iron to steel in small converters; the casting of the steel; and the annealing of the steel. Much ordinary carbon steel is made and, also, considerable special material, notably manganese steel.

Cast iron of course is the main material for the foundry. Brass founding is much more restricted in tonnage and scope, and the metal also is melted usually in crucibles. The latter product cannot compare in structural diversity with that made in the former and more important branch of founding.

Furnaces. Cupola. Most foundries melt their iron in shaft furnaces, called cupolas, with the aid of coke and a little flux. Cupo- las range in internal diameter from 20 inches to 10 feet. The proper mixture is charged into the cupola as it melts down, while ladleful after ladleful is tapped out of the crucible as the proper amount collects inside. If the cupola is large enough to run continuously, the metal will be poured from a large receiving ladle into smaller ones for transfer to the molds.

Open Hearth. The best cast iron is made by melting the pig in small reverberatories or in open-hearth steel furnaces. This keeps the phosphorus and sulphur of the fuel from getting into the iron, and admits of making large melts of uniform and precise specifications.

Molds. Varieties. For some purposes the molds to receive the metal are made of iron or steel; usually they are of a porous, tena- cious, and highly siliceous sand. The molds may be made up of a

Metallurgy 35

damp mbrture inside proper supports; and they then will be termed green-and molds. If the mold is baked hard after the shaping, it will be known as a dry-sand mold.

Cast Iron. White. White cast iron has all the carbon in the combined condition as produced by proper composition and quick cooling. This white, or chilled, iron is used for carwheel rims out-

Fis. 21. Medium-Grun CobI Iron, Showing GrBfihite. PEsrlite, nod Cemeatite

side a spider of gray iron; it is used for crusher jaws for roll shells, for the rolls of rolling mills, or wherever a hard resistant surface is demanded.

Gray. Gray cast iron should contain little or no free carbide but should have the carbon mainly as graphite; it is used for number- less objects, from kitchen utensils to engine beds weighing many tons. Often gray-iron castings are made soft enough to machine with steel tools and so to be of precise dimensions.

36 Metallurgy

Malleable, For making malleable iron the castings are first made chilled; they are then taken from the molds and assembled in rooms, to be heated for some days to a bright red heat while the carbon separates in the amorphous state. and the metal assmnes the properties of quite pure ferrite.

Specimen Stnccture. Fig. 21 shows what a rather hard cast iron looks like when polished, etched, and magnified 200 diameters. The black spots are graphite; they make cast iron soft and lubricate the cutting steel. The white spots are free carbide; this substance makes iron hard and brittle and dulls the cutting tool; soft iron should have no such white spots, for all this carbide (FcaG) should have decomposed to ferrite and graphite while the iron was hot. The intermediate gray areas are pearlite; it is this substance which makes iron strong. An iron composed entirely of this structure would be a steel, and could be treated and used just as all steels are; one sees that irons and steels really are related closely. The high carbon content of irons, usually present as graphite, is the main differ- ence between irons and steels.

Expert Ability Required. In the foundry there is much about the cupola requiring extensive scientific and technical kno\yledge. Conditions of mixing and melting cannot be studied too thoroughly.

The preparation of the molds is another department demanding expert knowledge. The production of the shapes, the composition and character of the sands, the manipulation of the patterns, and the finishing of the objects all call for scientific as well as for prac- tical attainment. In the more numerous small plants one often sees founding unfortunately botched by ignorant management and labor.

Wrought Iron

Process. At one time, wrought iron was far more important, relatively, than it is, now. As a matter of fact it is surprising that the process can survive at all. The process is essentially a melting of pig iron, a burning out of the phosphorus and carbon with the aid of iron oxide, and a final massing of the ferrite — now of much higher melting temperature — with working and shaping through rolls into commercial bars. Simple coal-fired furnaces are used.

Status. The furnaces used are necessarily of limited size; fuel consumption is excessive; labor is arduous; and the product is

Metallurgy 3?

anything but uniform. To a considerable extent the industry has fallen into busheling or bundling steel scrap in a reverberatory furnace somewhat larger than the genuine puddling furnace, then putting it through the regulation finishing as for real wrought iron. The product hardly can be considered desirable.

Wrought iron holds its small place largely through custom and its ability to weld easily. It is most excellent for many purposes, but it has a losing fight against steel that is equally good and cheaper.

Manufacture Of Steel

CARBONIZtNQ SOLID IRON

Process. This, is the oldest method of making steel; it is known as the cementation process and practically is superseded at the present iinie. The process consists of heating wrought iron in a pack- ing of icharcoal to a high enough temperature so that the solid solu- tion of cementite in iroil will gradually diffuse through the entire metaL , As formerly carried out on a relatively large scale, and as now carried out to, a limited extent, especially atSheflSeld, England, long bar& of wrought iron were packed in large receptacles, the char- coal filling up between and around the bars. This whole receptacle — eipiclosed within still another wall, as in a furnace — was brought up to beat gradually and was maintained at something over 700° C . during 7 to 10 days loner, depending on the grade of steel to be produced. Though the process is extremely inefficient, and the product equally varied, it survives in its modern application ls casehardening.

Modern Casehardehing. Casehardening h the production of a thin layer of steel on the outside of a much lower carbon metal. Recent practice does not confine itself to using charcoal alone, but, depending on the material and purposes, the carbonizing medium may be either charcoal and highly carbonaceous materials, or carbon- bearing gases, or even molten solids which may give to the iron object part of their carbon.

Casehardened objects are fairly common in ordinary life and have especially useful application in that the center of the material may be strong and tough although its exterior will be hard and brittle and take a fine polish. Such objects are common in aU sorts of machines, such as bicycles, automobiles, and wherever ball bearings and wearing surfaces are found.

38 Metallurgy.

Crucible Steel

Process. Original. The invention of the process of making crucible ateel by Huntsman, near Sheffield, England, in 1740, was a great advance in the art of making steel. He melted bars of cemented steel in small crucibles and thus got ingots of much_ greater uniformity. In succeeding decades men learned how to melt purer iron with carbonaceous materials and to Introduce the requisite ' amount of manganese for makmg very high-grade material.

Present Method. As practiced today, wrought iron, or scraps of good-quality soft steel, are melted in fire-clay or graphite crucibles

Courtwj 0/ The Coiaaial Sleet Company, FULsbarnh, PmiMvimnia

holding about 100 pounds of metal in furnaces heated by coke or gas. The requisite amounts of carbonaceous alloying ingredients will be dissolved, as the metal liquefies at a necessarily very high temper- ature, and, after standing for some time to become a perfect liquid, the metal may be deoxidized with a bit of metallic aluminum and then poured carefully into ingot molds.

Fig. 22 shows the men working at such a crucible furnace. Such a furnace is hardly more than a melting hole into which are led the pre-heated gas and air to combine about the crucibles. The furnace is

Metallurgy S9

run regeneratively, as will be explained further in the section on Open-Hearth Steel, with the gas supplied by gas-producers. One gets a good idea of the size of the crucibles, of the intense heat, and oif the methods of handling the crucibles from this picture.

Status. The manufacture of crucible steel still is carried out on a considerable scale, but, as the process never has overcome the defects of extremely small melts and much hand labor, it has lost relatively, in comparison with the tonnage processes. The process requires much skill, and is even yet being perfected in various details. There still is a strong demand for such material, especially for high-grade alloyed steels with the remarkable properties developed by the use of nickel, manganese, chromium, and tungsten.

Bessemer Steel

History. During the fifties of the last century, Kelly, in the United States, and Bessemer, in England, both discovered that the carbon could be burned out of pig iron simply by blowing air through the molten metal. The Englishman was very fortunate in his aggres- siveness and the prevailing conditions, and in a few years Was able to develop his process so as to make a very good grade of steel immensely cheaper than it ever had been done before. Bessemer developed the furnace, almost as it is used today, and the process has been continued with comparatively little change since the time of his early successes.

Converter. All converters have nearly the same shape nd are operated in about the same way. Fig. 23 shows a round body with detachable bottom. The outer casing is of heavy steel plate. It is filled and emptied through the nose A. The current of cold air enters through the pipe C, and passes through the trunnion T. It enters the converter from the windbox B, passing through the tuyeres -F. The tuyeres are of fire brick 24 to 28 inches long, and have 19 holes inch in diameter, or 7 holes f inch in diameter. The trunnion rings N are fastened to the converter, which turns on the supports' for the trunnions. The bottom is coupled on with damps and can be removed and replaced with a fresh bottom in a few minutes.

Process. Principle. In principle, the process depends Upon establishing a bath of molten pig iron in a suitablei receptacle pro vided with apertures for blowing in air, which, when it comes iiit6

Metallurgy

contact with the hot metal, oxidizes with avidity whatever silicon, manganese, or carbon is present, and even may attack the iron itself, if the blowing is not discontinued just as the carbon is burned out. The metal thus obtained is alloyed with exactly the right amount of carbon and manganese and is cast into ingots.

Variations. Variations of the process consist in using phosphorus as the internal fuel, as can be done when using high-phosphorus

Fig. 23. Section of Round Body Converter with Detachable Bottom

pig iron and a converter which is lined with a basic instead of a siliceous refractory. By very careful work, and as practiced in some countries, the process can be stopped at exactly the right carbon content, without having first to burn oui all the carbon and then to put back the right amount. American practice has found that the latter is the quicker method and that it gives good results A sur- prising amount of heat is developed during the reaction, and the process must be regulated carefully. In using the acid process, one is unable to remove phosphorus and sulphur from the metal.

Metallurgy 41

This gradually has narrowed American practice down to the use of pig iron or what is known as Bessemer grade, and the process has suffered much in comparison with the development of the open- hearth process, next to be described, which is slower but can be adjusted more at leisure.

Future Possibilities. As Bessemerizing is the most rapid and eflBcient method ever discovered for making steel out of iron, its further extensive use may have considerable future as part of a complex process in which the phosphorus in pig iron wUl be elim- inated in the open-hearth furnace, the carbon elimmated in a con- verter, and the metal then considered finished — or given a further extra refining in an electric furnace which will bring the sulphur to a very low limit.

Open-Hearth Steel

History. Development of Regenerative Heating, At about the time Bessemer was developing his process, other men were per- fecting an improved reverberatory furnace. Steel-making tem- peratures had been obtained in small coke-fired furnaces, but were found impossible in large furnaces until Sir William Siemens tried the pre-heating of gas and air before allowing them to combine over the hearth of the furnace. Pre-heating the air, by the alternated passing of the waste gases and incoming air through a fire-brick checkerwork, made possible the attaining of a temperature entirely new for refractory furnaces. This is called regenerative heating; the checkerworks are called regenerators. The new furnace of course was developed largely with the idea of making steel in it, and it soon came into successful conunercial operation.

Status. The open-hearth furnace, with its accessories, has been brought to a high state of adaptability and eflSciency. It can be heated with any sort of combustible gas, oil, or tar; the manual labor has been reduced to the minimum by all sorts of mechanical appliances; and the tonnage capacity has been continually increased — many furnaces now are able to put through 300 tons in 24 hours. It is by far the most important method for making steel which the world has today. Its drawbacks are in its inability to change its temperature range quickly, and a rather necessary slowness in burn- ing out carbon, as the gas produced by a too rapid burning from

Metallurgy

Metallurgy

solid or liquid ingredients in such a large bath woul4 make the metal boil out of any reasonably sized furnace. Although it is such a well- established process at the present time, its combination with other processes, as mentioned in the section on Bessemer Steel, has more than pretensions for such possible future usefulness.

Furnace. Fig. 24 is a section through an open-hearth furnace of a European plant. It is a tilting furnace moved by the hydraulic piston as indicated. The furnace is charged from the working plat-

Oil Pipe

Fig. 25. rercpectivc Diagram of Open-IIearth Furnace Courtesy of American Institute of Mining Engineers

form, and the metal is poured from the spout on the opposite side. The checkerwork for heating the gas and air is indicated in the center of the section and below the furnace level. The dust chamber is at the end of the flues directly down from the end of the furnace; a passage leads to the checker chamber. From the checkers ducts lead to the right to the gas and air inlets and to the stack; the valves are located here. In this figure all dimensions are in millimeters.

A perspective giving an excellent idea of the relative positions of the furnace, ducts, checker room, and dampers is shown in Fig. 25.

44 Metallurgy

This furnace is oil-fired, so only the air has to be pre-heated. The diagram shows how all the dampers are reversed when the waste gases are switched from one checker room to the other. The student should follow the actions of all the valves which result from reversing the air cylinder and from adjusting the air-regUlating screws* The draft through the stack is depended upon to pick up the gases from the hearth and to pull them through the regenerators.

Variations. The open-hearth furnace may be either stationary or tilting; its hearth refractory may be either siliceous or basic; the walls and roofs commonly will be of silica brick; the ports at each end of the hearth which admit the heated air and pass the burned gas suffer much from the high temperature and now usually are made sebtional so that they can be replaced without interrupting operations except for a few minutes. Flues lead from the ports down to the chckerwork where the air and gas will be pre-hekted. If either oil or tar is used, pressure steam will blow the liquid into the furnace through a nozzle, and only air will have to pass through the checker- work. Sufficient valves are provided in the flues for reversing the currents and for regulating the draft. It is not unusual now to find waste-heat boilers beyond the checkerwork so that the gases coming up the stack will have given up most of their available energy.

Process. In the process using a basic bath, the pig iron used is preferably rather high in manganese so as to remove as much sulphur as possible during the process. Scrap material is a common ingredient of the charge; iron ore also is used; while varying amounts of lime will be added to combine with the phosphorus present as it is oxidized and removed as slag. After some hours, the phosphorus having been slagged away sufficiently and removed, and the carbon being reduced to about the right percentage, the metal is tapped into a large ladle, deoxidized with metallic aluminum, and the manganese brought to the right specification by the addition of f erromanganese, and then, after standing a few minutes, the steel is teemed from the ladle into the ingot molds.

Modified Forms, The process can be hastened by certain modifications, which gives rise to the special processes known as the Talbot process, the Monell process, the Campbell process, or to the use of a converter to finish the metal after the phosphorus has been eliminated.

Metallurgy 45

Inqots

Defects of Solidification. We have learned in considering the general properties of metals that they always crystalize upon solidi- fication. This is eminently so in the case of the molten steel solidi- fying in the large ingots of commercial operations. These masses of steel, often weighing many tons, aggravate the segregation of impuri- ties by the necessarily long time which elapses before the interior of such an ingot becomes entirely solid.

Segregating. Because of this characteristic solidification phe- nomenon — th,e growth of the crystals from the exterior to the heart of the ingot during the solidification — it is found that ordinary ingots exhibit wide variations in their chemical compositions. Car- bon may vary many per cent of its total amount, as between the outer shell and the core. Phosphorus often is worse in this respect, and the same is the case with sulphur. Elements which form solid solutions with ferrite in the cold show little tendency to segregate. It is those elements which are thrown out of solution in ferrite — and in so doing form low fusing alloys and eutectics — which not only segregate most but are injurious because of this segregation in the finished material. This is known as segregation in steel, and is one of the great features to contend with in modern practice.

Piping, Another phenomenon exhibited by steel in solidifying is the contraction of the metal during the solidification and cooling of the solid; the effect is that the metal solidifying in its exterior portion has a solid shell formed, against which the molten interior gradually is contracting and solidifying. Obviously, a hole will be left in the very heart of the ingot when all of the metal has become solid. This cavity is called the pipe. It is a very serious defect in any ingot, because, if it is not removed, it will leave a flaw in the finished steel.

Blowholes. Another defect in many ingots is caused by gases, which were perfectly soluble in the molten material, extruding into little blowholes as the metal assumes the solid state. This condition possibly is more peculiar to converter practice than to any of the other methods, and it needs the most careful technique to overcome it fully.

Specimens. As shown in Fig. 26, Ingot No. 1 plainly is damaged seriously by the presence of the large blowholes throughout the

46 Metallurgy

entire metal; as the steel solidified, this gas generaUon even forced the metal up in the mold. Ingot No. 2 has a few blowholes about the outside of the ingot and a core of conspicuously segregated metal, the pipe is small. Ingot No. 3 has a most aggravating pipe but is otherwise sound; to cut out the piped part as discard would mean losing half the ingot. Ingot No. 4 is sound with a big cavity in the feeder head ; when this head is cut away, 95 per cent of the ingot may

Fl(. 26. Three Bad IngnU soil One Good One. Showing the Method of

Testing the Steel lOKots

CouriHii Ihe Amerian Imlitule of Minivv Engineer!

be sent to the mill in perfect condition. The first three ingots show what may happen in ordinary practice; the fourth shows what scientific study will accomplish.

Remedying Defects. The presence of small particles of solid foreign materials — like slag and oxides — in the ingot as well as of defects like cracks and checks, is a matter of faulty operation and does not require the serious study to overcome as in the case of segregation, pipes, and blowholes.

Metallurgy 47

Methods. To overcome all these defects is one of the serious efforts of current study. We know that small ingots, as a rule, ate not affected as seriously as the large ingots, but it 13 seldom .prac- tical to resort to this. Bottom casting of the ingots is not infre- quently used and gives a much better met'l than the ordinary teeming,

A pouring basin on top of the mold may be a step in the right direction but is only a partial remedy. Casting ingots with the big end uppermost, and with the mold very thick at the base, much reduces the defect due to the pipe. The intrusion of a can of thennit into the very bottom of the still molten metal at the proper moment has proved efficacious and worth using. Squeezing the ingot whil6 the core is still partly molten of course will close up any cavity and give a solid ingot. Heating the top of the ingot and keeping it .molten as long as possible will concentrate the cavity in the very top of the ingot and prevent much metal being wasted when the ingot is cropped preparatory to rolling.

Particular chemical composition to a certain extent can regulate the amount and position of any blowholes which will be formed. Finally, the technique of deoxidizing arid recarbonizing will have an extreme effect on the solidity and uniformity of the solid ingot. Gases must be removed as completely as possible while the metal still is molten; slag particles g,nd particles of oxide must be floated to the top of the bath while the metal is held fluid. This chemical and physical purification is accomplished by using the proper deoxi- dizers in exactly the right amount. The most common deoxidizers are aluminum, ferromanganese, ferrosilicon, ferrotitanium, and ferrovanadium.

Mechanical Treatment

Importance. The mechanical treatment of steel, through its influence on the structural units of the metal, is as important as any phase in the production of a suitable finished product* It has the most profound result in perfecting the physical internal structure of the metal, as well as in shaping it for the use desired. The four great methods of shaping metal are' (1) pounding or hammering; (2) rolling; (3) squeezing in hydraulic process; and (4) drawing through dies, as in the making of thin bars and wires. Each of these

48 Metallurgy

methods of shaping is especially eflScient in making products of certain shapes and will be favored on that account.

Hammering. Hammering is the most ancient method, and is used largely still, in connection with the crucible process. Hammers have been built to very large size, but are subject to certain mechan- ical defects and cannot compete with other methods of forming in the shaping of most objects. Hwnmering gives an especially good working of the surface layers of any object, but, as the impact is so transient, the core of the metal is less worked by this than by any of the other three methods.

Rolling. Rolling of the metal is the most rapid of all the processes for shaping. If the metal is used at a rather high temperature, it will offer little resistance to shaping and can be passed through the rolls at an extremely rapid rate. Care must be taken always that rolling speeds are not too great nor the exterior layers drawn by excessive differential motions. .The effect of squeezing in rolls is more prolonged than by hammering, and rolled material may have a weP V. orked core. The metallurgist is especially interested in this mechanical kneading of the metal as it passes through the rolls, but also must be thoroughly familiar with the mechanical side of the treatment.

Mills. Rolling mills are built in conjunction with nearly all steel plants, and shape up the material into billets, slabs, bars, plates, rails, structural forms, and the other simple shapes used in commerce. Of the divers sorts of mills for work- ing everything from ingots to finished shapes we can show only one — blooming mill, or that for the first passes of large ingots. The self-acting rollers of the tables at both ends of the rolls. Fig. 27, hurry the heavy lengths of metal into the gap between the two horizontal rolls which revolve now in one direction, now in the other, according to the pass. Each time the rolls will be closed a little between passes so that the ingot soon is reduced much in cross- section and is made longer. The driving mechanism is in the room at the right; the gears to make both rolls turn together are in the box at the right end of the two spindles which are coupled to the actual rolls. Above the roll frame is the mechanism to raise and lower the rolls as the pass demands. The motors to drive the live rolls of the tables are in the center foreground.

Metallurgy 49

Pressing. Hydraulic presses with their slower movement give the most penetrating compression to metal and cause a more thorough

deformation than any of the other methods. For this reason the internal fine grain so desired is better attained in this than in any other working process in use. Fig. 28 is a picture of an enormous

50 Metallurgy

bydratilic press about to reduce the size of an ingot. With many turnings and squeeze after squeeze such a broad thick ingot gradu- ally will be drawn out into gun tubes or shapes for other objects.

Hydraulic Press Elements, While the parts of a press such as can be seen in Fig. 28 are essential and comprise as their principal features the upper and lower forging bitts properly connected

Metallurgy 51

the main columns supporting the hydraulic compression cylinder and the two side lifting cylinders, the movable head, the attach- ments for turning and moving the ingot, etc., yet the mechanical means for supplying the power to the press and causing quick and repeated actions are equally essential and have made a great success for the machine.

Drawing* Wire drawing gives good internal working to a metal but of course is limited to the peculiar forms which can be made by such a process. As a matter of fact, the strongest metal ever produced has been made by a suitable combination of anneal- ings and drawings.

Heat Treatment

Ordinary Materials. Heat treatment of steel is a matter of the utmost importance and is absolutely essential for making the best materials. It is fortimate that the mechanical shaping 6f steel is done commonly at a temperatiu'e which gives the material good properties when finished. Thus, in the making of things like steel beams or steel rails, the heating and shaping have been carried out together, and, as the metal cools off, it is suitable for use. The lower the carbon content of a steel, the less the heat treatment will affect its final condition.

Tonnage Prodvjction, These general statements are good for materials requiring no unusual properties. Thus rail steel needs to have only the normal structure for a steel of the right manganese and carbon content to give normal material. If the manganese is about right, if the carbon is medium — that is from 0.50 to 0.75 per cent — and if the material has been rolled properly, there results a good material for rails. The same in general holds for structural steel, while in the case of many sheets which are of lower carbon steel, they are suitable for use as they come from the rolling mill. In the great tonnage of steel production it is essential only that the chemical composition shall be right approximately and that the mechanical working shall have been done at a suitable temperature with normal cooling.

Special Materials. But there are many more cases, not so much on a tonnage basis as for small units for special uses, where the normal material would be utterly inapplicable. These in particular

52 Metallurgy

are where objects are to be of hardened steel, and where they should be of tempered steel. We can get hard materials by the right chem- ical composition and with slight attention to any heat treatment, but, by having the carbon content exactly of the right amoimt and by cooling the material suddenly, very hard steels can be produced without further alloying.

Tempered Steels. All such hardened steels are apt to be unduly brittle and suitable for use usually only as the cutting or wearing edge of an instrument or tool. But by taking this hardened material and heating it carefully to such a temperature that the austenitic structure will begin to break up into the structures more stable at lower temperatures, we are able to get materials which will be inter- mediate and have not only considerable hardness but much increased strength and toughness. These in general are the tempered steels; they are the steels in which great tensile strength is required and which are especially desirable for innumerable uses, since, with the great strength, the bulk or size of the object can be kept small. The tempered steels are particularly useful for all sorts of tools and implements, and also are used widely in all classes of machines. Most of the working parts of the distinctively modern machines, such as flying machines, automobiles, and submarines, as well as innumerable locomotive and stationary-engine parts are made of such materials.

Effects of Temperature. Working Limits. The temperature at which metal is to be worked should be graded entirely by the finish- ing temperature which well may be about 700° C. The more mechanical working there is to be done, the higher must be the initial temperature; on the other hand, an initial temperature of over 1150° C. hardly is to be desired; accordingly, with much working to d©, this means that reheating is the logical conclusion.

Variation of Structure. Again, the most quickly chilled steel will have an austenitic structure, and a steel just annealed to full softness will have a very finely pearlitic structure. The various stages through the changes from this first to this second stage corre- spond to the decomposition stages of the solid solution and to the formation of the pearlite; they are designated mrtensite, troostite, osmondite, and sorbite. Tempering is the production of one or more of these special structures; it makes no difference how the structure is obtained.

Metallurgy

TABLE VI Chemical Composition of Ferrous Materials

Material

Elements Present Otheb Than Ibon (Per Cent)

Total

Free

Mn

Si

P

S

Ni

W

Cr

Iron:

Cast

ChUled

Malleable

Wrought

Electrolytic

Ingot Steel:

Castings

Rails

Structural

Tool

Nickel

Manganese

Silicon

Armor plate

High-speed

Vanadium

.01)1

.OUi

u6

.1— .i

1 s

.70 '

o

In practice, tempering may be a chilling somewhat slower than a real quenching, as in molten, lead or in oil ; or it may be a chilling in a water or a brine solution, and a subsequent reheating imtil the proper structure is developed, which will be made permanent by chilling from the second drawing temperature. The cutting edge of a tool which has been quenched is reheated by withdrawing it and letting the heat from behind follow down until the drawing is exactly right, after which the entire head of the tool is quenched.

In the high-speed steels these structures are spread out and highly differentiated, and are obtainable with much precision. In the straight carbon steels it is difficult thus to separate them, so that the most expert knowledge is required to get a thick piece of the same tempered structure throughout.

Many Factors Affecting Material. In studying such an arrange- ment as that in Table VI, it must be kept in mind that the chemical specification is no more than one of many factors determining the quality and the properties of the material. The method of manvr facture, whether crucible, Bessemer, or open-hearth furnace, or the acid or the basic process; the manner of shaping; the heat treatment; the physical properties, such as tensile strength, are all often just as important as chemical composition.

54 Metallurgy

ELECTRIC FURNACES IN IRON AND STEEL MANUFACTURE Furnaces for Pig-iron Production. Electric furnaces for making pig iron are meeting with some success in centers where electricity- is cheapest and where iron ore also is available; this is possible in localities in the Scandinavian countries and in California.

Arc-and-Reeisiance Type. Fig. 29 is a diagram of an electric furnace making pig iron; it is the combination arc-and-resistanee type, continuously operated. The construction of this furnace

SxCT-iOff /iT/iO' SacTiott /itCZ>'

Fig. 29, End and Side SeclioDBl ElovstioDe of ao Electric Fiunww tor Pic Iron Cawtati of tilt 'Tron Agt"

differs somewhat from that of others which are in use but the prin- ciples and chemistry involved are the same in all and will be obvious after having studied the iron blast furnace. A furnace like that of Fig. 29 is heated by the current through the electrodes as indicated in the cut. The coke fed in with the ore effects the main part of the reduction; gases formed by the combustion may be circulated up through the column of ore to give as much pre-heating and reduction as possible.

Furnaces for Making Steei. Electric furnaces for making steel excel in that no current of gas has to pass through or over the metal, and in the high temperature which can be obtained readily. Only

Metallurgy 55

where electricity is wonderfully cheap, do these furnaces prove economical in the reducing of iron from its ores, in the melting of cold metal, or in the comparatively low temperature heating and slagging period which is necessary for the removal of phosphorus from the metal.

Pure-Arc Type. Fig. 30 is a section through the Stassano pure- arc type of furnace. The electrodes are entirely above the charge which is heated by radiation. Mechanical arrangement provides

for turning the furnace about to give motion to the bath. Quite a number of these furnaces are in use.

Combinaiion Type. The furnace most used resembles the type of Fig. 31, which is of Heroult make. It is obviously a tilting fur- nace. No electrodes are shown in place in the picture but are to be inserted in the two large holders suspended above the furnace. Such furnaces require many thousands of amperes, with the voltage usually less than lOO; the electricity is for heating only, the heat is partly from the are between the electrode and the slag and partly because of the resistance through the bath. The current comes in at one electrode and goes out at the other.

56 Metallurgy

Advantages of High Temperature. The electnc furnace has a real field of usefulness in the final removal of sulphur from a partly purified bath, because we can get a very liquid slag and a very basic slag hy using sufficiently high temperature, such as cannot be obtained in any other type of furnace. Electric furnaces, of course, may be lined with either an acid or a basic refractory, depending on whether we wish to make an acid or a basic slag. As intimated by the possibility of sulphur removal just mentioned, most furnaces now are lined with basic material.

The most common type of electric furnace ja the combination arc- resistance type in which the heat is partly devel- oped by the arc between electrode and slag and partly by the resistance which the slag and metal offer to the passage of the current. Extremely high temperatures thus are attainable, and thinly fluid slags often containing much cal- cium carbide are ob-

Fig, 31. Heroult Type oi ElcMrio Steel FiirnaoB tained, which WOuId be

Courttai, 0/ ihc iroa Ag, absolutely infusible in

any other type of furnace. Such a high-lime slag is very efficacious in fluxing off even small amounts of sulphur from the metal. Other- wise, the chemistry of the electric furnace is no different from that of other types of furnaces. Carbon is easily introduced by adding varying amounts of pig iron, or is burned out by adding iron ore.

Status. The tonnage of electric steel is increasing year by year, and furnaces holding 20 tons in one charge are now operating. Of the 215 electric steel furnaces in the world (1915) 75 are of the type of Fig. 31. All the furnaces now in the world have a combined yearly capacity of over a million tons of steel.

H4

Metallurgy 57

Miscellaneous Metals

Copper

Important Characteristics. In the United States coal is the most valuable mineral product, pig iron is the next most valuable, and copper comes third with a yearly production of over a half million tons and a value of over $150,000,000.

Although in a general way copper is not nearly so vital to our mode of existence as iron is, since iron is the basis of our activities, yet copper allows variation in color and finish, and — through its extensive application in all electrical work— gives a breadth and convenience to many sides of our life which now would be discarded with much regret.

The mines and plants from one end of the country to the other are open to visitors, and the industry seems permeated with broad-minded and kindly-disposed men who do not fail to grace the literature, until it is a better reflection of the industry than is the case with any other technical subject of which the author knows.

The great hydrometallurgical copper mine of the world has been at Rio Tinto, Spain; that will still continue to be a great mine, but will be dwarfed by the tonnage and technique of the remark- able Chuquicamata mines of Chili which are now being brought, to capacity by American enterprise.

Copper Minerals. Copper occurs in the following forms:

Native Copper. This is the mineral of the Lake Superior copper mines, and it occurs also in many other ore deposits.

. Cuprite. The red oxide, CU2O, a mineral very high in copper, enriches many western deposits.

Tenorite. The black oxide, CuO, is a less important mineral but is found frequently in many mines.

Malachite. The green carbonate, CuC03.Cu(OH)2, is a very conspicuous and important surface mineral.

Azurite. The blue carbonate, 2CuC03.Cu(OH)2, of ten accom- panies malachite.

Chryscolla. The silicate, CuSiOa. 2H2O; also is a surface mineral.

Chalcopyrite. The copper pyrites, Cu2S.Fe2S3, form the universal and most important copper mineral. .

58 Metallurgy

Covellite. The sulphide, CuS, is found as one of the main deposits of the Butte district.

Chalcocite. The mineral, CU2S, is very common and important in many western mines.

Bomite; Enargite; and TetrahedrUe. These are complex minerals of note.

Brochantite. The basic sulphate, CuS04.3Cu(OH)2, is the mineral of the Chuquicamata mine.

REDUCING COPPER ORES Methods. Of the several methods of reducing copper ores outlined below there are now only two of minor importance — strong reduction, and pyritic smelting for sulphide ores. All the others at present are operating on very extensive scales. The old Welsh processes of roastings and reductions are of only theoretical and historical interest.

I. Smelting by Fire Treatment Alone.

(A) Oxide ores smelted in blast furnaces to black copper.

(B) Sulphide ores smelted in blast furnace to matte;

matte converted to blister.

(1) Strong reduction for low-sulphur ores.

(2) Semipyritic smelting for medium-sulphm* ores.

(3) Pyritic smelting for high-sulphur silicious ores.

II. Combination Wet and Fire Recovery.

(A) Reverberatory smelting to bullion and slag.

(B) Mechanical roasting; then reverberatory smelting

to matte. IIL Hydrometallurgical Recovery,

(A) Sulphide ores leached with acid solution, and copper

precipitated as metal with iron.

(B) Sulphate ore leached with acid solution, and copper

precipitated as cathode metal by electricity.

Oxide Copper Smelting

Process. Smelting oxidized copper ores to black copper, as the metal thus recovered is called, is one of the simplest of all smelt- ing operations. The ore with flux and coke is charged into a suitable cold blast furnace; the metal is collected in the crucible until enough is present to tap out into the ingot molds.

Metallurgy 59

Pig. 32 shows in perspective and section a round copper blast furnace; the larger rectangular furnaces are built with close adher- ence to the proportions as seen in the round type. The interior is rather short and wide — not much height is required to effect reduc- tion of the metal; water jackets inclose the smelting zone and the charge column up to the feed floor. The metal collects inside until

enough has accumulated to tap out into slabs or bars; the slag likewise is tapped intermittently from a level slightly above the metal tap. The gases will go to waste directly, or after simple elimination of the coarser dust.

Where Used. This type of smelting is apt to be found on frontiers where the surface ores are awaiting this easy treatment. The process had a very noteworthy run on the surface ores in Arizona

60 Metallurgy

before the enormous development of the deeper sulphide ores which are being mined today. A furnace doing this identical work can be seen in operation almost any day in the city of Chicago.

The most remarkable case of oxide smelting in blast furnaces is to be found at Katanga, in Central Africa. Huge rectangular furnaces made in the United States are run there by United States men on the largest oxide deposits (excepting the sulphates of Chili) which have yet come within the range of blast furnaces.

An oxide blast furnace necessarily is limited by the generally meager extent of such ores; from the fact that it is difficult to make clean slags economically, small mines will prefer to turn over their ores to large sulphide smelteries where they can be treated equally well with the regular sulphide ores.

Sulphide Copper Smelting

Strong-Reduction Type. Conditions of Operation. The smelting of coarse sulphide of copper ores is a type of reduction which has developed in different chemical aspects, as well as in furnace capacity. As indicated in the outline, some occasions have required the development of a smelting which much resembles the strongly reducing conditions of lead and iron smelting. This is to conserve the sulphur and to assemble all of the copper in a matte or artificially enriched sulphide compound of iron and copper. Sulphur and copper have a remarkable affinity for each other, and, with conditions at all reducing, they will go through the furnace imchanged and come out together as matte for further treatment to make blister copper.

Usage, A few occurrences of this type of smelting have been found noteworthy but there is little use for the process at the present time. The most conspicuous example is at Mansfield in Germany.

Matting Furnace. Construction. Fig. 33 shows a copper- sulphide furnace which illustrates well the features as now in use in this very important method of copper reduction. The crucible is made very shallow and is set on jacks so that the bottom of the furnace not only is kept cool but is removable easily. The smelt- ing zone is water-jacketed thoroughly and, from the picture, it is seen that not only is the breast well water cooled but the matte spout is likewise. The tuyeres are arranged closely together along

62 Metallurgy

both sides of the furnace, and it will be observed from the picture that the water overflow from each jacket comes out to the drain pipe entirely exposed so that the attendant can see always exactly how much water is going through any single section. The top of the furnace, which of course will be above the feed floor as the furnace is arranged in the building, is made of brick, and the gases leave through a large steel flue. The opening at the side allows of charging the full length of the furnace.

Operation. Sulphide furnaces of course are all charged mechan- ically, the cars usually dumping the material in along the side of the furnace. A further consequence of the large tonnage is that slag and matte are run off continuously into a forehearth or settle where the separation of matte and slag takes place. We know that in connection with oxide-copper furnaces internal crucibles are necessary, because of the easy chilling of metallic copper; with matting furnaces, however, the fiery matte is just as apt to cause trouble by eating through its container, and preferably is gotten out of the furnace as quickly as possible. From the matte settler the slag will be run off as overflow into slag pots, while the matte will be tapped out from a lower level and taken to the converters.

Semipyritic Type. Characteristics. Semipyritic smelting is so called because, to a certain extent, the sulphur in the ore is utilized as fuel; this means that the coke in the charge can be kept much lower than in a real reducing fusion. It depends on the fact that the copper will go with what sulphur is left, even though a portion of the sulphur is burned out by the blast. Furnaces operating on such a basis commonly have a very large volume of air blown in and there is no necessity for a high ore column, the flames often playing entirely through the charge.

Importance. In the semipyritic type of sulphide reduction, there is the greatest development of sulphide copper smelting. This constitutes a very great use for the blast furnace, and at one plant smelting lump copper ores in this way we have the largest blast furnace ever constructed, which will treat some 3,000 tons of charge in 24 hours.

Semipyritic smelting is the great blast-furnace process in the western States and likely will continue long to be so, in so far as Imnp sulphide-copper ore is available. It used to be of relatively

Metallurgy 63

moreimportance before the developmentof reverberatories. Theblow- ing of fine particles of the charge out of the furnace to make flue dust

always was troublesome and now is taken care of entirely by smelting concentrates and fine materials in reverberatory furnaces.

64 Metallurgy

Typical Plants. A large plant for this sort of smelting with all the supplementary facilities for handling the ores, flue dust fumes, and gases the converting of the matte, and the necessary power production, constitutes quite a metallurgical community. Such plants are situated at Anaconda, and Great Falls, Montana; Garfield, Utah; Kennett, California; Clarksdale and Douglas, Arizona; and Cananea, Mexico.

A typical one is seen in the illustration. Fig. 34, which shows the Cananea smeltery from the hills above the plant. From a distance the conspicuous objects are the ore bins, and bedding plant, the mills, the huge stacks, the enormous flues, and the mul- titudinous buildings, each for a specific operation in the plant.

Pyritic Type. Process. Pyritic smelting utilizes the sidphur in the ore as almost the entire source for the smelting operation. It is found that with a sulphide ore and siliceous gangue there is available from the burning of the sulphur and from the formation of ferrosilicate just about enough heat to accomplish the smelting operation successfully. On account of this close heat margin it is seldom attempted to run without a slight addition of coke, although such has been done when occasion demanded it. Other than in the use of this internal fuel, the chemistry of the process is exactly the same as in any sulphide smelting. Matte of course is the product of the fusion.

Usage. Small plants have been operated on this principle in

Montana, and at Leadville, Colorado, but the greatest plant for

this type of smelting has been and still is in operation at Mt. Lyell,

Tasmania.

Roasting Copper Ores

Field. With the exploitation of the low-grade porphyry and copper mines of the western States and the production of enormous quantities of fine sulphide-copper concentrates, the mechanical multihearth roasting furnace has found a wide field of application The outlet for these concentrates is by means of reverberatory smelting, and their sulphur content first must be lowered con- siderably in order to bring the concentration of the copper in the matte high enough for Bessemerizing in converters.

Mechanical Roaster. The mechanical roaster for this fine sul- phide ore has several hearths; the ore is fed in at the top, dry, dhij

Metallurgy

most of the sulphur b burned out by the current of air over the hearths as the ore descends from one to the other on being worked across each hearth by the rabbles. The calcines preferably will be trammed hot to the reverberatory.

Stage of Perfection. There are several excellent mechanical roasters on the market, differing somewhat in manner of drying the ore, in the construction of the hearths, in the means for cooling

and rotating the rabble arms, and in the facilities for admitting the air to cany out the oxidation.

Mechanical roasters of the general type illustrated in Fig. 35 have been brought to a stage of very high tonnage production and of extremely cheap treatment cost per ton. Furnaces are run to treat as much as 100 tons in 24 hours on one set of 20-foot hearths, while the total cost of operation will probably be less than 25 cents a ton. The perfection of this type of furnace has strengthened the development and stability of reverberatory smelting enormously.

66 Metallurgy

Reverberiitory Copper Smelting

Present Development Copper reverberatory smelting, in its most essential features as practiced today, is one of the most interest- ing technical developments of the generation; from little furnaces treating hardly more than 20 or 30 tons a day in 1880, their size has grown until now they are built 25 feet wide and 140 feet long, and will smelt up to 800 tons in 24 hours.

The most remarkable advance has been in fuel economy and in general furnace eflBciency. Particularly, it has come to be appre- ciated that the secret of rapid smelting is a suflScient excess of hearth temperature over the formation temperature of the slag. From the old coal-burning fire box there has been developed grad- ually the use of gas, oil, and powdered coal as far superior means of producing the enormously long flame required to heat the furnace properly.

In the mechanical construction of the furnace, reverberatories have been greatly improved, while the physical structure is now made of a size which a very few years ago could have been proven impossible.

Reverberatory Furnace. The copper reverberatory is essentially a huge heated receptacle in which the charge is melted down. It is on this basis that its attainments have been so remarkable. The furnace is depended upon now to oxidize considerable of the sulphur of the charge, while the matte and slag produced hardly differ from those produced in the copper blast furnace.

Typical Features, The general proportions of a modem rever- beratory furnace fired with pulverized coal are seen in Fig. 36. The furnace is essentially an extremely long but rather broad and thin melting box. From the burners at the firing end the hottest part of the flame spreads out and covers the bath up to the section where the roof is lowered; the picture indicates that this is about at that point where the matte is tapped off. Immediately above this hottest section are the hoppers for letting in the charge. The charge has a long way to travel and abundant opportunity to separate into matte and slag before it reaches the skimming door situated at the opposite end. Slag will be skimmed near the end farthest from the burners, while the matte commonly is tapped off at about one-third of the total distance from the burners, and is sluiced directly into

Metallurgy

Hi

'1?

68 Metallurgy

the converters, or is handled in ladles. It is noticed that the fui nace is built massively and is held together thoroughly with a great number of steel I-beams placed entirely about the furnace walls.

Reverberatories usually are equipped with waste-heat boilers for recovering as much heat as possible the exit gases. Convert! nE Copper Matte

Converter. Lining. Copper matte produced either in blast furnaces or in reverberatories is poured into large receptacles to be blown to what is known as blister copper. A few years ago these

steel-bound receptacles were lined exclusively with siliceous material, and, in burning out the sulphur and the iron from the matte, this siliceous material was depended upon for making slag with the iron oxide produced. Metallurgists recognized the disadvantage of this consumption of the lining of the furnace and of the frequent renewals, and it is due to the efforts of two eminent metallurgists, Smith and Pearce, that, in 1904, converting was accomplished successfully in converters lined with basic material which would withstand indefinite operation,

isa

Metallurgy 69

We now are able to maintain the integrity of a converter lining for many months. The siliceous material required for the formation of the iron slag is added as necessary during the conversion of the matte to metal.

Operation. The size of the converters has increased continu- ously until they now are built 20 feet or so across. These enormous barrel- or pear-shaped steel monsters are tipped back and forth by hydraulic or electric power for charging, blowing, and pouring. A picture of some of these largest pear-shaped converters is seen in Fig. 37. The nearest one is upright and the matte is being blown as is seen by the light at the mouth of the converter. The second converter apparently is red hot inside and may be just pouring the metal or may be in some other stage of the process which requires tipping over so that the contents will run out. As the converter is in this position, the tuyeres and the air box are fully exposed high in the air; when tipped back in blowing position, they evidently are so placed that the air will squirt through the bath of red-hot matte inside.

Chemical Principle. The principle of the chemical change in the converter is that, when air is blown through the metal, the sulphur and iron are oxidized and practically are removed before the copper itself is attacked. Some of the sulphur and all of the iron will be oxidized to leave what is known as white metal, sl prac- tically pure sulphide of copper, after which the blowing will be continued until this all is changed to metal by the complete elim- ination of the sulphur as sulphur dioxide.

Usage. Converters are a necessary accessory in all large sulphide smelting establishments, and change the matte into metal at a cost of a small fraction of a cent per pound.

REFINING COPPER METAL Furnace Method

Practical Necessity. The great bulk of copper as produced in converters and as turned out is by no means pure enough for refining by electricity; in fact the electrolytic refining of copper is possible commercially only when the metal to be refined already is of very high copper content. Because of this, if the blister copper is not melted in a reverberatory at the smelting plant, it necessarily is

To Metallurgy

done at the copper refinery, which may be located at some point better situated for the obtaining of cheap power — the most essential feature of electrolytic refining.

The furnace refining of nearly pure copper is, then, an essential step in the production of merchantable material. It is carried out extensively at all copper refineries, both on blister copper and on the cathodes produced by electrolytic refining. The different sorts of blister copper are susceptible to extensive furnace refining, but the melted cathodes require it in slight degree only and that largely for the exact regulation of the final oxygen content of the metal.

Partial Separation of Metals. Furnace refining can almost completely remove iron, lead, tin, sulphur, manganese, and zinc; arsenic and antimony are partly removed by this refining, but it will have little affect on selenium, tellurium, bismuth, or the precious metals. This accounts for the fact that furnace refining is an essential operation, yet is unable to produce a commercially pure copper as demanded in the trade.

Process. Ooddation. This furnace refining of copper consists in melting down the copper in a large coal-fire reverberatory, during which melting considerable of the impurities will be oxidized and floated on the surface of the metal. More extensive oxidation can be effected by flapping the metal with iron paddles or by blowing in air through iron pipes. This process of oxidation, however, intro- duces undue amounts of oxygen, which is absorbed by the metal and retained in solution. The oxidized slag having been removed, the excess of oxygen then can be taken out of the metal by covering with charcoal and thrusting in logs of wood, which, decomposing in the hot bath, use up and remove the oxygen.

Electrolytic Method

Usage. Nearly all crude copper is electrolytically refined; this means that after the metal has been smelted to black copper, blister copper, or any sort of crude cakes, they are remelted and some- what purified in an anode melting furnace and cast into anodes. The anodes are refined in the electrolytic cells and the cathodes melted, before their final exit from the refinery as ingots, slabs, and wire bars.

This type of refining is applied to most of the metal won by the

15S

Metallurgy 71

reducing methods referred to previously — the main exception is some of the Lake Superior copper which is refined in the smelting furnaces, as it Vas originally quite pure.

Complete Separation Effected. From a reasonably pure anode, as results from the remeltingof blister copper in the refining furnace, electrolytic refining is able to produce a metal of the most extreme purity, except in that particular element, oxygen, which again will be introduced in the final remelting as will be necessary to make shapes, ingots, slabs, and wire bars.

The trade demands at the present time are extremely exacting, and most of the copper of commerce, therefore, is put through this process of electrolytic refining. Further than this, electrolytic refining effects an extraordinarily complete separation of the precious metals, the removal of which it is equally difficult to accomplish by any furnace process.

Process. Arrangement of Electrodes, Electrolytic refining consists of dissolving copper from an anode immersed in a strongly acid solution of copper sulphate, of forcing the electropositive particles of copper through the solution, and of plating them out on a sheet of pure copper suspended close to the anode; the particles coming out on this near-hanging strip of copper will constitutie the cathode; the force accomplishing this transfer is of course the electricity which is supplied to these thousands of couples in great quantity by the generating system in the refinery. It is common to hang about twenty of these couples in an acid-proof tank, which is about 3 feet wide, 4 feet deep, and 10 feet long. The electric current is sent through each tank, with the respective anodes and cathodes arranged in parallel. A number of tanks will be put in series and arranged in groups to accomodate the amperage and voltage most suitable as generated by the large dynamo units.

Action of Electrolyte. The electrolyte is kept at a very definite concentration of copper and free acid and is maintained in active circulation through the vats at a constant temperature of between 60° and 70° C. The electrolytes of different plants average close to 4 per cent of copper and 12 per cent of free acid. Anodes waste away rapidly due to the solution of the copper and in about a month's time are taken out and new ones substituted. The cathodes are taken out more frequently, when the freshly deposited copper

r2 METALLURGY

is stripped from the starting sheets, and the sheets are put uiu;k again for a new layer.

The anodes which are taken out of the vats are washed to remove the slime and then are remelted into full-sized anodes to be

put again into the tanks. Fig, 38 indicates a series of these anodes as lifted out from one of the tanks, which are seen together in the other view thickly packed on the floor of the large electrolyzing room. SepaTatian of Dor& Metal. A large quantity of sediment collects in the bottom of the electrolyzing vats and is washed off from the

Metallurgy

anodes when they are cleaned. This mud is carefully removed from the vats and collected by itself in large tanks for further treatment. It contains the impurities originally present in the anode, of which the most important are gold, silver, palladium, and platinum. Selenium and tellurium also are imdesirable components of this mud. This mud is washed, its copper content largely depleted with a Bulphuric-acid treatment, the selenium and tellurium oxidized away in a small reverberatory, and a metal known as dor6 metal

Blast Furnace*

Origin of Material Troatad.

-—

Bevorbermtory

Copper Mattl.

Electrolytic Refining plant.

Daaie Lined Converten.

Copper Anodes.

Eleetrolyte Purifying PfauiC

Starting Sheet Electrol ytic Refining Tknka.

I ' n TL.

starting Electrolytic Impure Anode

ShccU. Slime. Electrolyte. Scrap.

H:

fe

Commercial Electrolytic Refining Tanks.

Cathodes.

Electrolytic

Slime.

Impure

Electrolyte.

.-

Anode

Scrap.

Concentrating Tanks No. 1.

Crystallising Tanks.

r

r

Mother Liquor.

Insoluble Anode Tanks.

Blncstoiw.

r

Slag

Furnace Refinery.

Wire Bar. Cake and Ignot Copper for Market.

Purificatfon Impure

Slime. Etectrolyte.

Concentrating N j. 2,

Precipitating Tanks.

Filter Press Waah Water Added.

Puriflcatioli

Slime.

-4—

Purified Electrolyte,

Waab Electrolytic Slime.

Water. 21%HsO

Steam Drying Tables.

Electrolytic Slime.

10<jbHsO Silver Refinery.

Fig. 39. Flow Sheet of Copper Refinery Courtesy of American JnstUtUe of Mining Engineers

finally obtained which goes to the silver refinery for separation and recovery of the gold, silver, palladium, and platinum.

Diagrammatic Summary. Fig. 39 may be studied to advantage as a summary of the coiu'se of materials and processes in a refinery. It is necessary that the diagram take up the material as produced by blast furnaces or reverberatory furnaces and that it turn out market copper or partly dried slimes to go to the silver refinery. The main electrolytic treatment for the bulk of the material is on the left-hand side of the diagram; the right-hand side is devoted

74 Metallurgy

to the course pursued in purifying the electrolyte, a small portion of which is being separated continuously and treated to get out the acciunulating impurities. This diagram may be studied in every detail to much advantage.

Silver Refinery For A Copper Plant

Supplementary Treatment. There are only a few copper refineries to work up the entire tonnage of the metal produced in this country; the amount of precious metals found in the blister copper is considerable, and it therefore results that there is a good deal of material to be separated and provided for in a sUver refinery.

The dor6 metal which is obtained from the preliminary fusions just mentioned is cast at those same furnaces into anode shapes and electrolyzed in nitrate-acid solution to obtain a deposit of remarkably pure silver on the cathode. The silver thus obtained will be merely remelted in large crucibles and cast into bars for market. From the electrolysis of these anodes a residue results which contains all the gold, palladium, and platinum originally present in the copper ore. These metals will be assembled and separated by either wet or electrochemical means to be cast finally into bars of pure gold, palladium, and platinum.

Importance. The silver department of a copper refinery thus is quite extensive in its scope and really handles a surprising amount in money value. As several of our largest companies operate both lead and copper refineries, it is common to draw the dore metal from the different refineries together in this same department; thus the American Smelting & Refining Company at its plant at Maurer, New Jersey, gets the precious metals from various plants and operates the largest silver refinery in the world.

Lead Lead— Silver Smelting

Relative Importance. The smelting of lead is one of the impor- tant metallurgical industries of the United States, and we are able to produce considerably more Jead than any other single country. Workable deposits of lead ores are found throughout many western States, as well as in Wisconsin and in Missouri.

Metallurgy 75

But, although the lead-smelting industry itself is of very con- siderable magnitude, its importance is still further enhanced because lead is used extensively as a collector for precious metals. By this, we mean that many gold and silver ores are used as fluxes in lead smelting, or even may be put thus into the lead smelting charge for the sole purpose of recovering their gold and silver contents along with the lead.

Recovery of Precious Metals. It is common to work up secondary precious metals by smelting industrial residues with leady materials at industrial centers, like Chicago and New York. Some western plants likewise are virtually gold and silver smelters. A large part of the tonnage smelting may have its main value in the precious metals, and barely enough lead is put in the charge to carry out the function properly in a lead blast furnace; that is, enough bullion to keep the crucible in good running order.

It has been described how the precious metals accompany copper throughout the winning of that metal, and in the same way the precious metals go through all the processes in the recovery of metallic lead and finally are separated in the pure state. Thus, in studying the metallurgy of copper and lead, we cover a large section relating to the winning of gold and silver.

Lead Minerals. The lead minerals occur as follows:

Galena. The imiversal lead mineral is galena, PbS, which occurs as the main one of all our deposits.

Lead Carbonate. The carbonate, PbCOs, is a surface mineral commonly found as an oxidized ore over deeper deposits of original sulphides.

Lead Sulphate. The sulphate, PbS04, is another oxidized mineral and may accompany lead ores in general to a slight extent.

Lead Silicate. The silicate, Pb2Si04, possibly is a more important lead mineral and sometimes constitutes a rather important ingredient in the ores of certain mines.

Lead Oxide. The oxide, PbO, mixed with other metallic oxides may be found in some surface deposits.

All of the surface oxidized ores are reduced very easily in the simplest way and are used up only too quickly whenever the mines are vigorously exploited. Digging deeper into the ground, the miner most always begins to produce a larger and larger per cent of his

76 Metallurgy

material as sulphides which possibly are concentrated from a rather lean original ore. Thus the lead smelter is confronted in general with higher sulphur ores and finer materials. LEAD ORE REDUCTION Reverberatories. Considerable pioneer work has been done both in this country and in Europe to develop lead smelting in reverberatory furnaces, but the process is now about extinct; If it

Fig. 40. Men Working at Lead Ore Heanh

is attempted to smelt galena in a reverberatory, there first must be a roasting or oxidizing interval before the main reduction can be accomplished. The process, therefore, is out of line with rever- beratory development so successfully evolved in the one-reaction processes with other metals.

Hearth Smelting. The ore hearth is an ancient appliance somewhat modified by later improvements. It consists of a basin to hold the melted lead and to support the charge to be smelted.

Metallurgy 77

Sides restrain the fire while air is blown in from the back through holes which are placed above the level of the lead but under the surface of the charge.

Fig. 40 shows this accurately. A kettle for the smelted lead, a car for the residue, and hoods and a pipe to lead away the smoke about complete the equipment. In the picture the men are shown in front of the fire spreading out the charge and stirring it over and over, as must be done unceasingly.

Chardcieristics. The ore hearth has the advantage of requiring no mechanical accessories besides the blower; it is started and stopped at a moment's notice and has an output depending only on the supply of ore and labor.

The great disadvantages of hearth smelting are that only a por- tion of the lead is recovered directly, while the remainder partly divides between the gray slag, the flue dust, and the lead fume which is produced in excessive quantities. Working up these latter materials requires blast-furnace smelting which thus has to consti- tute a part of the plant after all.

The ore hearth may be considered as a furnace in which con- siderable lead is recovered and the remainder of the charge is left in a roasted condition ready for normal blast furnace smelting; In this sense hearth smelting is treatment preparatory to blast furnace smelting.

Fot Roasting. Roasting was accomplished for many years in long hearth reverberatories by hand stirring of the charge (see Fig. 11). During the 90's a new sort of roasting was introduced from abroad where it had arisen, which consisted in blowing air through an , ignited charge to both roast and sinter at the same time; the process was developed by Huntington and Heberlein and was called pot roasting for short. Within the last dozen years an improvement of this method rapidly has replaced [all the older ones in many plants.

Roast-Sintering. Down-draft roast-sintering is a truly remark- able process for desulphurizing and sintering lead ores preparatory to blast-furnace reduction. The charge is made up with the idea of having just enough metallic sulphides present to support a progres- sive combustion and to agglomerate the material fully. Fig. 13 is to be studied in detail again, while Fig. 41 is a side view of the same machine in action.

To Metallurgy

Operation. At the very left of the pictiire and at the top ia seen the feed hopper which is fed with a conveyor with the well-mixed and moist charge. As the hne of pallets, each carrying 3 grates, moves under this hopper it becomes burdened with a layer of charge and passes next under the small oil burner. From the burner the grates slowly move toward the right over the suction box, seen between the upper and lower lines of pallets, while the fire eats its way down through the cake and should be through by the time the

Fig. 41. Side Viev of CoDtiDuous Rasat-SinUrinc MasUiia

material has passed over the box and is to be dumped off into the car which is in waiting.

The grates pass around the sprocket wheel at the discharge end and return under the suction box to come up again for a fresh layer of charge in passing under the feed hopper. The roast-sintering process is striking in its simplicity and is highly satisfactory as. to the results obtained.

Lead Blast-Furnace_SmeUinE

Inrtance. Aside from the lead made in ore hearths ali our lead is now won in blast furnaces. This makes blast-furnace smelt- ing of lead ores an extremely important topic.

The lead blast-furnace plant has its departments for sampling the materials, for" storage of everything, for sintering, for power,

Metallurgy 79

repairs, and means to settle flue dust and to cool and filter the gases. American plants usually dross the lead in 30- to 50-ton kettles, and then send it to the refinery.

Furnace Features and Operation. Both round and rectangular furnaces are conunon, the latter being customary in large plants. The peculiar features developed in America have been the siphon tap for the lead, full water-jacketing of the fusion zone, patent tuyeres, and mechanical feeding. Fig. 42 is an excellent picture of a round furnace in an European plant as partly improved with siphon tap, and partly water cooling.

At the base of the furnace is the steel-bound crucible and the enlargement on the side which constitutes the lead well out of which the lead is pouring into the small kettle. The circular shape of the entire shaft may be seen plainly; the cast-iron posts support the bustle pipe and the steel shell of the top. This furnace appears to be water cooled only about the breast and the tuyeres. The slag tap is on the right-hand side of the furnace, while the lead which runs out the well is ladled into the molds seen in a row in the immedi- ate foregroxmd.

In the lead blast fm-nace the strength of reduction is not nearly so great as in the iron blast furnace; the temperature in the smelting zone is not nearly so high, and the fuel required on the charge is sev- eral times less. A calcium-iron silicate slag always is made; a little piatte always is formed to settle out in the forehearth or the pot pettier below the slag. This matte carries the copper of the charge, as well as lead and values, and so is separated carefully and worked over for its metals.

Bag Houses. Flue dust is recovered in large brick or steel chambers and ducts, the latter made long enough so that the gases will be cool enough to enter safely the cotton or woolen bags at the bag house. All United States lead plants have bag houses.

Characteristics. Bag houses are wooden, iron, or brick struc- tures surrounding enough long porous bags to filter the solid parti- cles from whatever gas may have to be treated. The cellar com- partments receive the fume-laden gases and the collected lead fume falls down into the same ceUar whenever the bags above are shaken. The top of the cellar is the floor of the bag room; this floor is hardly more than a support for row upon row of iron thimbles about which

Metallurgy

Metallurgy 81

the bottom ends of the bags may be tied. The main chamber of the ba house is hung thickly with bags 30 feet long and IS inches in (Uameter, which bags may be of cotton or of woolen fabric. Such a bag room may contain from 100 to 1,000, or more, bags; large plants commonly put partitions through so that one section may be repaired or cleaned while the others cany the load.

Fig. 43 indicates crudely something of the nature of this acces- sory. More often the structures have stacks instead of the openli along the roof as indicated. Bags may be shaken by hand, by mechanical means, and by reversing the draft with an awdliaiy fan. The frequency of shaking may be once a day or every few hours.

Status. The bag house is firmly established as aa integral part of all lead nelting plants, both small and large, and is justified fully from the financial point of view as well as by being necessary from the hygienic point of view.

' METHODS OF REFINING LEAD Electrolyzing. Lead is now refined in four large plants by electrolyzing in fiuosiUcate solution. The main advantage is the recovery of bismuth, but, even with the recovery of bismuth, it is questionable if it is the more economical process. Parkes' process is the method commonly used.

Parkes' Process Principle. Parkes' process depends on the fact that. If zinc is dissolved in molten precious-metal bearing lead and the mass is

82 Metallurgy

allowed to cool, the crystals first separating carry nearly all the noble metals together with much zinc and lead.

Operation. SepaT<aion. of Metals. The process is executed by meldng the lead in large kettles and by heating with zinc to about 1 per cent of the weight of the lead until the zinc, which has a little higher melting point, is dissolved. The lead is cooled slowly, and the

Fig. 41. Paber du Faur Tilting FutnaCB

crystals which eventually ben to fonn throughout the mass are skimmed off and placed to one side. This Is continued until the lead begins to chill as a mass. The lead is heated again and the process is repeated. After the second skimming the lead is heated and run out into refining furnaces where the dissolved zinc; -0.65 per cent, is eliminated by.standing in the hot furnace or by blowiBg.

Metallurgy S3

air or steam through. The lead then is run out and is molded into 100-pound bars for the market lead of commerce.

Practical Requirementa. There are, of course, many details that cannot be enumerated here; it ought to be said that the lead as it comes from the blast furnace usually requires a preluninary oxida-

Fig, 45. English CupelUtioD Furiuwe

tion, or softening, to get rid of all its dissolved copper and antimony; the zinc must be stirred most thoroughly into the molten lead, usually by mechanical means; the crusts are best squeezed to rid of as much lead as possible; the molding may be by hand, by siphoning off into a circle of molds with a movable trough, or by pouring several molds at once oq a conveyor.

84 Metallurgy

Retorting Furnace. The zinc crust which is removed from the desilverizing kettles is taken to a retorting furnace like that shown in Fig. 44. It is called a Faber du Faur tilting furnace; inside is a retort which is heated by the oil burner seen at the side near the bottom. The zinc is distilled oflF and collects in the condenser which is hited on in front. This condenser on front is nothing more than a retort which has become unsafe to use further for holding the heavy charge inside. It is seen that the furnace is mounted on trunnions so that the rich lead can be poured out after the zinc has been elim- inated. The zinc is volatilized from the retort and condenses in the outside receiver from which it is tapped at intervals into the cast-iron mold seen ready on the carriage.

Cupellation. The rich lead from the retort next is taken to the cupel furnace in which the lead is eliminated and the precious metals are left by themselves as dor6 silver. The cupel furnace is operated as indicated by Fig. 45. It consists of shallow oblong hearth in which is melted the rich lead; it is supported on wheels so as to be drawn out; it is adjustable so as to tilt up or down by the operation of the screw wheel seen in front; it is surrounded by brick walls with a good draft up the flue; from one side the flame from coal or gas plays Qver the metal while from behind a blast of air squirts 6nto the bath to oxidize the lead. The litharge formed by this oxidation floats to ihe front and dribbles over the breast to fall into the little pot in front of the man. The adjustment is kept so that only the very uppermost or siuace layer — the newly formed litharge — can flow out ; the metal is kept behind on the hearth. In this way the operation proceeds until all the lead has left the bath and only silver remains.

The final bullion left on the cupel hearth is the final concentra- tion of all the precious metals originally in the ore. For electrolytic refining, it is taken to a silver refinery as described in the section under Copper; or, the silver may be dissolved out with sulphuric acid, the metal precipitated with copper, and, after collecting and drying,, may be melted to fine silver.

Zinc

Ores of Zinc. Occurrence. The United States is especially favored in the matter of zinc ores and so is able to produce more of the metal than is any other nation. In New Jersey occurs the

Metallurgy 85

mineral, willemite, which yields large quantities of an exceptionally pure metal. In Wisconsin and Missouri are the numerous mines whose ores smelted in the central States afford high-grade metal and make this the leading section of the country. Throughout the west- em States are many other mines, some of them enormously large, whose ores are mixed with minerals of other metals and which yield large tonnages but poorer quality stuff.

Mineral Forms. Zinc sulphide, ZnS, is the primitive mineral, but the carbonate, ZnCOs, is quite an important mineral, and some silicate and some oxide come to light now and then. The carbonate may be calcined before smelting, although it usually is charged direct into the retorts. The sulphide must be roasted first before being available for reduction. If the ore is not well roasted, it causes serious loss; on this account zinc ores commonly are roasted far better than are either copper or lead ores.

ZINC ORE IlEDUCTION

Zinc Characteristics. The properties of zinc are such that the metal is;not recoverable like iron, copper, and lead, which we have been studyinjg. Zinc melts at 419.4** C. and boils at 940® C. Its rjeductioh temperatiu'e is about 1050** C. Zinc is reduced to meUd above its boiling point Zinc vapor also decomposes carbon dioxide and at once reverts to zinc oxide. No blast furnace yet has been induced to produce the metal; it can be obtained only by reduction in small retorts with a large excess of carbon.

Two Types of Roasting Furnace. Sulphur Dioxide Lost There are two chief types of furnace for roasting zinc ores. In the first type the flames which heat the ore play directly over the charge; the products of combustion and the sulphur dioxide from the roasting mix and pass up the flue together. All zinc furnaces are built with mechanical arrangements for stirring. In this first sort of furnace the ore and the flames enter at opposite ends; the ore gradually is worked to the fire end of the furnace under constant stirring. If 12 per cent is the amount of sulphur left in a mechanically roasted copper ore and 4 per cent is the amount in a roast-sintered lead charge, the permissible sulphur in a roasted zinc ore is more like 1 per cent.

Sulphurous Gases Separated. The second type of furnace lacks the innumerable variations found in the first class of furnaces.

86 Metallurgy

They must keep the gases of combustion separate from the sulphur- ous gases, and the sulphurous gases are to be kept as concentrated as possible and used for sulphuric-acid manufacture. This second type of furnace is muffle built; there will be seven superimposed hearths with the three lower ones muffled so as to be heated with extraneous fuel. These furnaces have to be stirred mechanically, as do all zinc-roasting furnaces. The use of so many hearths, the muffling of the first three hearths, and the ducts for pre-heating the air and

leading it into the furnace and for leading the gases out make a struc- ture difficult to describe and even harder to draw.

Zinc Distillation Furnaces. Retorts. The retorts for holding the charge during zinc smelting are about 5 feet long, 10 inches in diameter, inch thick, and closed at one end. Several hundred such retorts will be placed nearly level in a long double furnace which is heated by gas, either natural or producer. It b now customary to have three or four rows of these retorts one above the other and as many as a thousand of them in one block. The retorts tip slightly downward so that they can be filled and cleaned easily.

OperaHon. The best practice pre-heats the gas and air in regen- erators, and the gas is burned by letting in air at intervals in just

Metallurgy 87

the right amount to furnish a uniform combustion the length of the furnace. Fig. 46 shows the external appearance of a large furnace in operation. The flame is seen playing from the end of each con- denser as the monoxide escapes into the air. These furnaces will be charged only once a day, the smelting cycle completing itself in about 24 hours. Too high a temperature of course is not desirable because of its effect on the retorts; otherwise it is highly desirable to have a large excess temperature in the furnace to replace the heat absorbed by the reaction and to keep the reaction going Uvely.

The metal is graded and sold on specification, and refining is accomplished by redistillation; this latter is not done very often, as may be assumed.

Cadmium

Usage. This is a very useful metal for low-melting alloys and for electroplating. Otherwise its uses are limited. No ores are known; it is recovered as a by-product from zinc smelting.

Fractional Smelting. Cadmium distills over at a temperature considerably lower than zinc does; it thus can be concentrated in the first metal vapors which come off during zinc smelting. This first enriched material is distilled two or three more times, when a nearly pure metal is furnished. Most of the cadmium of commerce is recovered by this fractional smelting of German ores. All the Missouri zinc ores are said to contain 0.5 per cent of cadmium on the average; this practically never is recovered in this country, and the price of the metal usually is something under a dollar a pound.

Gold Recovery Of Gold

Methods. Placer Mining. Of the four main channels through which our supply is derived, the simplest and most ancient method for recovering gold is by washing sands and gravels which contain it in solid particles. This method is used in all parts of the world where gold occurs in loose material in sufficient quantity; it is called placer mining.

Milling and Amalgamation. If gold occurs in solid rock, as it does in many places, the rock must be crushed to free the gold which can be recovered by washing over copper plates amalgamated

88 Metallurgy

with mercury to catch and retain the particles of gold as they are washed over. This type of recovery is called milling and amal gamation.

By-ProdUcis. We have already indicated that much gold is recovered iii the smelling of copper and lead ores; such metal might be called byprodvet gold, for it is recovered incidentally in the working up of these other metals.

Cyaniding. Another highly important method for recovering gold wherever it occurs in minute particles, as it usually does in solid rock, is by treating the very finely crushed rock with a dilute solution of sodium cyanide or potassium cyanide. Fine gold is dissolved easily by such a solution, and the gold can be recovered by treating the solution with a more electropositive metal, such as zinc or aluminmn, when the gold will be precipitated out and can be filtered ofiF, dried, and melted into bullion.

Placer Mining

Variations. Simple Equipment. Placer mining can be carried out with the very simplest outfit, such as a gold pan, a rocker with riffles, or a sluice box whose bottom is suitably roughened to collect the heavy particles of gold which are inclined to wherever they can find lodgment. Mercury usually is sprinkled on during the operation to assist in the recovery by catching the particles of gold and by drawing them within the heavy globules of the esrtremely heavy liquid.

Hydraidicking. An extension of the simpler placer-mining idea is carried out by hydraulicking with water under pressure, so that loosely cemented gravel banks can be worked just the same as ordinary gravels.

team Thawing. Another extension is by thawing frozen gravels with steam points, so that the dirt can be subjected to conunon sluicing methods.

Dredging. A final refinement of placer mining is to use dredges to dig through whole banks of gravel whenever they occur under water. These dredges will float in rivers, lakes, or artificial ponds, as they dig up the gravel with continuous digging eqmpment at one end, wash the gravel on board the boat, and finally discharge the refuse a.t the other end to make new ground. Fig. 47 shows one of

90 Metallurgy

these huge dredges at work. The digng ladder is at the left, the discharge behind at the right. The gold recovered will be put in shape on board to be handled by the United States mint.

Milling and Amalsamation Process. Improvements. The simpler methods of milling rock by dropping stamps on the chunks and of recovering the gold by amalgamation has received much refinement in recent years- Other types of grinding machines, concentrating machines, and

accessory apparatus have been introduced to advantage, Cyaniding accompanies amalgamation in some cases.

Cyaniding

Process. Milling. The full recovery of gold from a crushed ore usually demands very fine grinding. The plants have been meeting the requirements and now have tube and ball mills of continually improving duty.

Solution. If the cyanide solution has not been introduced in the grinding it will be added immediately after. Its best effect always.is produced in the presence of enough aeration and agitation

Metallurgy 91

to allow fully the reaction indicated in the following which is the common equation for the chemistry of the process.

4Au+8KNC+0,+2H/) 4AuK(NC),+4KOH

Special tanks for this purpose have been devised which do the work quickly. Other chemicals may have to be added at this time, for any acidity is to be neutralized with lime, and some ores require further oxygen carriers.

Separation. When the gold finally is in solution, the solid matter of the pulp may be separated by decantation or by filtration; both operations are extensively used.

Fig. 48 indicates to what refinement the filtering devices have advanced. These huge filter leaves are immersed in the pulp, and the solution is sucked through until a cake has formed, after which the whole row of leaves is transferred to another tank for washing, then to another for discharge of the barren pulp.

The cyanide solution is run through zinc boxes, or is charged with zinc dust and then filter pressed; either of the processes gives the metal to be dried, melted with fluxes, and finally sent to the mint for parting.

Electrolytic Refining

Process. Electrolytic gold refining is used extensively in this country and abroad. The electrolyte is a hydrochloric-acid solution of gold chloride, and the transfer is made from anode to cathode, as in all such processes. This is by far the most precise method for separating gold from the other noble metals, which remain either as slimes or in solution.

Adaptability to Silver Recovery. This process is adapted to recovering silver, if certain modifications are introduced. We have already learned that silver is refined in exactly the same way. Thus, in describing copper and lead smelting, placer mining, and cyaniding, we have covered the metallurgy of silver as now , practiced.

Aluminum

Commercial Recovery. Although aluminum is the element next most abundant to oxygen and silicon in the earth's crust, the recovery of the metal is a distinctively modern metallurgical feat.

92 Metallurgy

For nearly 100 years aluminum has been known in the metallic state, but only since 1886 has the production of the metal been on such a scale that it has been of commercial use. The reason why we have not had ajuminum before is because of the difficulty of freeing it from the oxygen with which it is so intimately associated in nature.

Aluminum is one of the most useful of the common metals, and, with its application to a great variety of purposes, the necessary facilities for its production by low-cost electricity continually are being augmented.

Process of Reduction. We are able to reduce aluminiun from a mixture of the double chlorides of aluminum and sodium by the use of metallic sodium at a red heat. If a mixture of chemically prepared anhydrous chlorides with cryolite — a sodium- aluminum fluoride — is mixed with metallic sodium and charged suddenly into a hot reverberatofy furnace, the reduced alumi- num finally can be tapped out of the furnace into ingots. This entire process is very expensive and probably is not used at the present time.

Hall Process. The Hall process is the one most extensively used. This process, consists in electrolizing aluminum oxide in a molten bath of cryolite w:ith large carbon anodes to supply the current. The carbon electrodes necessarily are oxidized by the oxygen fred from the reaction; the aluminum collects in a layer below the fused bath and is tapped out at intervals into molds.

Critical Details. The process for making aluminum is extremely simple but is operated only with much attention to many critical details. The electric current through the furnace must be exactly right to keep the bath molten, as well as to effect the electrolytic decomposition of the aluminum. Only since we have been able to make suitable carbon electrodes has the process been possible com- mercially. Another extremely important detail is the exact chemical composition of the bath, which must be lighter than the fused metal; the two substances are of almost the same density in the molten state, and, unless the fused salt is kept slightly less dense than the aluminum, the latter would float, and not only bum but, of course, would disrupt the process entirely.

Metallurgy

Nickel

Occurrence and Use. This metal very much resembles iron in its properties. Its far more extensive use is precluded by nothing less than the natural scarcity of its ores. A few deposits of silicate mineral are known in the United States, but it never has been possible to produce the metal from them at a price to compete with the cost of production from the sulphide deposits of Canada and New Caledonia.

The uses of the metal most interesting to the metallurgist are as a steel-alloying element, for electroplating, and as the chief component of a nickelKJopper alloy known a:a Monel metal.

Nickel preserves its bright appearance remarkably well in ordinary air and therefore is used extensively as a coating or elec- troplate over more tarnishable metals. The electrolytic copper refineries produce some nickel from their electrolyte purifications which is available for this use.

Reduction. Canadian Process. The mining and early smelting processes, as carried out at the mines in Canada, are well known, but the companies attempt to suppress the later processes until we again see the metal and its alloys when ready for sale; At the mines in Canada the ores first are roasted, in the open or othierwise, then some type of blast smelting — blast furnace or converter — or, more recently, reverberatory smelting eliminates the gangue and produces a nickel-copper-iron matte. This is the end of the process as accomplished in Canada.

Mond English Process. The Mond process is supposed to be used by the company of that name in England; it depends on the fact that, by the use of carbon monoxide, the nickel can be volatilized and thus separated from the other metals.

Process in United States. The process in use in the United States presumably is that of separating the sulphides of the metals with sodium sulphide, the heavier nickel sulphide sepa- rating below the layer of the other mixed sulphides. After this separation the sulphide must be roasted to oxide and the oxide then reduced to metal. The metal thus produced is by no means pure; there* is apparently no difficulty ih producing a very pure metal by electrolysis of this crude metal, and such is on the market.

94 Metallurgy

Monel Metal. Monel metal is the natural alloy produced by winning the metal from the nickel-copper matte without separation, presumably by roasting, and then by straight reduction with carbon. This alloy analyzes approximately Ni, 67 per cent; Cu, 27 per cent; Fe, 2 per cent; Mn, 3 per cent; and Si and C each 0.5 per centi It is a strong, tenacious alloy, much like steel, but far more resistant to corrosion; because of the latter property it is finding much indus- trial application.

Antimony, Bismuth, Mercury, Tin

G)mmon Characteristics. These four metals are all reduced easily from their oxides without any difficulty at all. All four like- wise are perfectly stable at ordinary temperatures, while, at higher t mperatures, they do not decompose carbon dioxide and therefore can be won by simple reduction with carbon at a red heat. That they are such expensive metals follows from their relative scarcity in nature and not at all from the trouble of winning them from their ores. Their low melting points, ease of reduction, and moderate chemical activities make their winning a simple task for the metal- lurgist; when they occur in small quantities with other metals, it may be quite a different matter to separate and to recover them efficiently.

Antimony, Antimony is found chiefly as sulphide. This sul- phide can be treated with metallic iron to yield metallic antimony directly. The operation can be carried out at moderate temperature in any suitable receptacle. The sulphide likewise can be roasted to oxide by the simplest means; the oxide then can be reduced to metal with carbon. Neither process offers particular metallurgical difficulty*

Considerable antimony always is recovered in lead refining; this is turned out as hard lead (12 to 14 per cent Sb) ready for use.

Antimony is used as metal chiefly in the minor alloys.

Bismuth. Bismuth occurs sometimes as metal, in which case it can be liquated from its gangue and recovered directly as metal. If an ore contains sulphide of bismuth, it can be roasted; this roasted ore as well as oxide ores are reducible directly to metal without difficulty, and they are reduced best in reverberatory furnaces.

Bismuth is recovered in electrolytic lead refining; in this case, any bismuth in the lead goes to the silver refinery in the tank slimes.

Metallurgy 95

In the refinery it is separated from the silver by oxidizing fusions, is reduced to metal, and is refined electrolytieally.

The metal goes into pharmaceutical preparations and into alloys with low melting points.

Mercury. Mercury occurs in ore deposits mainly as its sul- phide, cinnabar. An oxidizing roast of this compound frees the metal which is condensed in suitable receptacles or chambers. The literature contains abundant accounts of the devices for accom- plishing this end. The metallurgy of the process is simple and most excellent results are reported wherever there is ore to treat.

Tin, Tin occurs chiefly as oxide in nature. This oxide is very heavy, and the mineral can be concentrated to a product high in tin. Concentration is effected by panning, by dredging, and by crushing and mill treatment. The concentrated mineral is reduced to the metal in either shaft or reverberatory furnaces.

It is rather necessary to have the concentrates as clean as possi- ble to prevent the reduction of the other metals which might accom- pany. The furnaces used are all small, and the tin on the narket is of surprisingly good grade. Tin is difficult to remove from other metals when it accompanies them, which, fortunately, is seldom

suspected.

Tungsten

Occurrence. This jnetal occurs sparingly in nature as tungstate of calcium, of iron, and of manganese. The minerals are conspicu- ous on account of their high specific gravity.

Reduction. Metal. The concentrated mineral is fused with sodium carbonate which forms the soluble sodium tungstate and allows the removal of the other metals by filtration. From this solution acids precipitate the oxide of tungsten, WO3. This oxide is reducible to the metal directly.

Fer TO- Alloys. For the production of the ferro-alloys the oxide will be reduced along with some iron to act as carrier. This is the W;ay it is put into steel. Ferrotungsten as reduced with iron in the electric furnace commonly runs over 70 per cent tungsten. There is a very great demand for the tungsten steels and their price often is well above a dollar a pound.

Modem Ductile Form. But tungsten can be reduced to metal mcM'e pure than this, when it appears as a gray powder without

96 METALLUllGY

displaying any sign of malleability or ductility. A few years ago the research laboratory of a great industrial company learned how to make this metal in ductile form. The more it was heated and worked, the stronger and softer it became. Thus was discovered the strongest, most dense, and highest fusing metal we have. Its uses have developed in other fields, although it is used more than ever for filaments in incandescent-light bulbs. The strength of tungsten wires exceeds even the strength of the strongest steel wires. The one great restraint on many uses for such a metal is that, although its melting point is about 3000° C, yet this heating must be done with exclusion of air, lest the metal bum up with a flash.

Sodium

Reduction Process. Metallic sodium can be produced by several of the most energetic straight chemical reductions at very high temperatures, but the electrolysis of its fused hydroxide has proved cheaper than any other method, and that is the process used exclusively today.

Electrolysis. The anhydrous hydroxide fuses at about C; if the molten substance is subjected to electrolysis just above this temperature, sodium and hydrogen will be liberated in chemical equivalents at the cathode, and the corresponding amount of oxygen at the anode. The operation is carried out in small pots holding about 250 pounds of the caustic. Through such a bath, suitably provided with anode and cathode and with means to keep the gases separate, some 1,200 amperes at 5 volts will be sent. The liquid sodium collects in a receptacle at the top of the bath and is dipped out.

Usage. If sodium chloride could be used instead of the hydrox- ide, the metal would be much cheaper; such a process has not been perfected. It is used for chemical purposes.

Magnesium

Electrolytic Reduction. Magnesimn is another metal which id produced solely by electrolysis. In this case the double salt of magnesium and potassium chloride is kept molten in an iron recep- tacle and is subjected to the passage of the electric current. Chlo- rine is liberated at the anode, and the magnesium, alone, separates at the cathode.

Metallurgy

Critical Details. The magnesium is not much lighter than the molten bath so care must be taken that the melt be kept as dense as practicable. Other salts, such as barium chloridci may be. added for this purpose. The details of the process of manufacture are guarded closely, although the normal cost of production, is consider- ably under 80 cents a pound. The novice finds much difficulty in getting rid of the chlorine, in preparing easily the pure anhydrous salt to be used, in collecting the magnesium together from the bath in which it diflFuses, etc.

Uses. Unlike sodium, magnesium has uses for its own metallic properties. It is the lightest of the available metals and makes alloys which are strong and tough. With the increase of aviation there certainly will be greater demand for this metal.

Another use for reasonably cheap magnesium metal would.be in deoxidizing other metals. Magnesium quickly combines with oxygen as found in molten steel or in other alloys, and would be .used far more extensively if the price permitted. It is astonishing from the metallurgical point of view that, with magnesium compounds so abundant and with the metal presumably separated with io undue difficulty, the price could mount to $5 a pound and remain there for an entire year, as happened during 1915.

Platinum, Palladium, Iridium

Supply. These three metals are growing continually more valuable because their supply is not increasing while their use is, both for industrial and ornamental purposes.

The U. S. Geological Survey gives the world's production thus:

Couktbt

1913 1914

Russia

300,000

300,000

250,000

241,200

Canada

New South Wales and Tasmania

1,500

1,248

Columbia

12,000

12,000

15,000

17,500

United States — crude

United States — all bullion

1,200

1,300

1,100

2,905

Borneo, Simiatra, etc.

314,328

315,029

268,333

263,453

As the production of palladium and iridium probably is not over 1 per cent of the total number of ounces, it is plain how inadequate their

'Ds Metallurgy

fiiply is. Practically this entire amount comes from placer deposits where the metal occurs as metallic grains containing 70 to 90 per cent of platinum and iron as the largest of a dozen other impurities.

Separation Process. Standard Method. The standard method of treating the metallic grains with aqua regia to dissolve the platinum gives a fair separation, but further treatment is necessary for the highest grade material. By this method the platinmn in aqua regia is evaporated and the salt is taken up twice with hydrochloric acid to prepare for precipitating from clean chloride solution with ammo- nium chloride. The bright yellow ammonium-platinic chloride is dried, is heated to platinum sponge, and the sponge then is melted before the oxyhydrogen blowpipe.

Commercial Form, A commercial sepa-ration, carried out on dor6 silver from copper and lead refining, consists in treating with aqua regia the residue from the sulphuric acid parting for silver. From the metals remaining, platinum and palladium will be dissolved, and iridium will be left. The platinum will be precipitated as the double chloride; palladium will be thrown down by metallic zinc and melted into cakes. The iridimn can be purified further by dissolving in silver and extracting again with acids. The main course of the procedure is simple, but the more the matter is studied, the less sharp the separations are found to be, and several treatments may be required to give strictly pure products.

Electrolysis. The wet treatment is not entirely satisfactory for recovering the gold from its bullion, so the electrolytic process already mentioned is in vogue largely now; this method, at the same time, separates palladium and platinum to go into the electrolyte and to be precipitated out, while osmium and iridium remain in the sludge and are recovered separately.

With high temperatures available, and with electrolytic sepa- rations to assist the wet treatment, the metallurgy of these metals js in a wiay to be used with much satisfaction, if the metals themselves only weire available in quantity.

Seven Alloying Elements

Silicon, Manganese, Titanium, Vanadium, Chromium,

Molybdenum, Cobalt

Adaptability for Ferro-AUoys. It is a significant fact that the

-above elements — to which may be added nickel and tungsten — make

Metallurgy 99

excellent alloys with iroa. They all are elements of high melting point; but whether they are oxidized easily at high temperatures, or not, makes little difference, if they are dissolved in iron. Their behavior is absolutely opposite to many low-melting elements which also alloy easily with iron and ruin it for all practical purposes — such elements are sulphur, phosphorus, arsenic, and aluminum.

Reduction. Cobalt is reduced easily from its oxide to metal, but most of the others require more energetic means. Silicon and manganese commonly are reduced with varying amounts of iron in the usual iron blast furnace, and their iron alloys are on the market in considerable variety and are used very much in steel making and in foundry work.

All of these elements can be reduced with iron in electric-arc furnaces; some, indeed, can be re- duced quite pure, except for carbon, which it is difficult to prevent com- bining under such cir- cumstances.

V.UU.O V p. TyiMcal Thermit Cnitible

Aluminotkermic CbtUsu at the CMirkmidl Thermit Company.

Method. But a method is

available which is used considerably now since aluminum has become reaaonably cheap; this is to reduce the purified oxide of the metal in question with metallic aluminum. This is called aluminothermics. A crucible like that seen in Fig. 49 commonly is used. The oxide, or the mixture of oxides, if an alloy is to be made, is mixed with fine granular aluminum and is placed in the lined steel cavity of the crucible. If the mixture is brought to reacting temperature at any one point, the activity spreads quickly throughout the mass, and in a few seconds the newly formed metal can be tapped out into suitable molds, A bit of ignition powder is used to start the reaction. The temperatures produced are extremely high, for the heat has no chance to dissipate in the few seconds of the reaction, and alumina has by far the highest heat of formation of any of the common oxides whose metals are used. The alumina formed by the reaction

100 Metallurgy

floats (it fuses at 2000 C.) on the metal reduced and can be recovered as a by-product.

New alloys continually are being developed by this process. Besides quite pure cobalt, chromium, and manganese, as well as their iron alloys, there are on the market ferrotitanium, ferrovanadium, and ferromolybdenum, and numerous other alloys produced by aluminothermics.

Index

Index

The page numbers of this volume will be found at the bottom of the pages; the numbers at the top refer only to the section.

Acid copper solution

Acid electroljrtic cell

Acid radical

Acker process of fusing salt

Active electrochemical cell

Addition agents in electroplating

Adherence of metal deposit

Alkaline copper solution

Alkaline electrolytic cell

Aluminothermics

Aluminum

commercial recovery

Hall process

manufacture of

process of reduction Alundum Anions Anode

Anode reactions Antimony

Aqueous solutions as lytic conductors Arc furnace

Arc-and-resistance type furnace Austenitic structure Azurite

B

Bag houses

Baser metals, electroljrtic refin- ing Bessemer steel

converter

future possibilities

history

process Betts process of lead refining

Note. — For page numbers see foot of pages.

electro-

54, 70,

Page

Page

Birkeland-Eyde procww

Bismuth

Blast furnace

actual operation

elements of construction

importance

pig casting

plan of operation

power plant

raw materia]

stoves

Blast-furnace lead smelting

bag houses

Cumace features and operation

importance

Bleaching powder

Blister copper

8, 12

Blowholes in steel

7, 19

Bomite

Boron as conductor

Brinell hardness tester

Briquetting ores

Brochantite

, 143

Burned deposit

By-product gold

By-products of refining copper

Cadmium, smelting

Calcining ores

Calcium carbide

Canadian process of nickel smelt-

ing

Carbides produced in electric

furnace

Carbon

as conductor

Index

*age

Page

Carbon (continued)

,

Converter 127

and electric furnace

Converting copper matte 156

and iron

chemical principle 157

Carbon bisulphide

converter 156

Carbonizing solid iron

usage 157

modem casebardening

Copper 145

process

copper minerals . 145

Carborundum

important characteristics 145

Casebardening

reducing copper ores 146

Cast iron

refining copper metal 12, 157

gray

silver refinery for copper plant 162

malleable

solutions for deposition of 23

specimen structure

Copper matte, converting 156

white

Cottrell process of fume precipi-

Castner oeU

tation .82

Cathions

8, 11

Covellite 146

Cathode

Crucible steel 70, 126

Cathode reactions

. process 126

Caustic soda, manufacture of

status 127

Cell

Crushing and cutting method of

electrochemical (see Electro-

sampling 102

chemical cell)

Crystallization of metals 94

electroplating

Cupellation 172

Cementation process

Cupolas 122

Chaloocite

Cuprite 145

Chalcopyrite

Current density, influence on

Chemical reactions

electroplating 21

Chemical solution or fusion

of

Current supply in electroplating 18

ores

Cyaniding 176, 178

Chlorine, manufacture of

D

Chromium

ChryscoUa

Decomposition of salt solutions 26

Circuit of electrochemical cell

electroljrtic hydrogen and oxy-

Cobalt

gen 37

Combination t3rpe furnace

manufacture of chlorine and

Combination wet and fire

re-

caustic soda 31

covery

manufacture of hypochlorites 29

Combustion, recovery of valuable

sodiuin chloride 26

products of

Deposit, quality of in electro-

Commercial electrolyzers

fer

plating 20

hypochlorites

Diaphragm cells 32, 35

Conductivity of conductors

Dore metal, separation of 160

Conductors, kinds of

Drawing steel 139

electrolytic

Dredging 176

metallic

Dry-sand mold 123

Coning and quartering method of

Drying ores 104

sampling

Ductile form of tungsten 183

Note, — For page nuwbert ee foot of page;

Index

Electric furnace 47, 109, 142

advantages oi eledrie frnnace 50

oonmiercial proceaBes 59 poflBibilitieB at hi tenqxra-

tuies 48

in sted industry 68, 142

types of dectric furnaces 54

Electrical discharge in gases 76

characteristics of discharge 76

fixation of nitrogen 79

production of osone 77

Electrical fume precipitation 81

Cottrell process 82 recovery of valuable products

of combustion 82

Electrical heating compared with

fuel heating 51

Electrochemical cell 6

action inside cell 7

anode reactions 12

cathode reactions 11

definitions 6

Faraday's laws 9

Mectrochemical equivalent 9

Electrochemical theory 2

electrochemical cell 6

kinds of conductors 2

Electrochemistry, applied 1-86

electric furnace 47

electrical discharge in gases 76

electrolysis 2

introduction 1

Electrodeposition 17

Electrodes, definition 6

Electrolysis 2 electrochemical theory 2 electrolytic refining and re- covery of metals 12 electroplating 17 fused electrolytes 41

Electrolyte, definition 6

Electrol3rtic conductors 4

characteristics 4

classification 5

conductivity 6

NaU. — For pao* numbers see foot of page*.

Electiuljflic hydrogen and oxygen 37

odb for decomposing wmler 37

plant equipment 40

types of cdb 39

uses oi hjrdrogen and oxygen 37

Electrol]rtic recovery of meiab 15 genial features of leeoveiy

process 16

gold from sea water 15

other metab 16

silver 179

Electrol]rtic reduction

of mjfcgnpaiiim 184

of sodium 184 Electrolytic refining of metals

12, 158, 179

baser metals 14

copper 12, 158

gold 14

lead 15

silver 14

Electrolysing, lead refining by 169

Electrometallurgy 89

Electrons 89

Electroplating 17

electroplating cell 17

factors in successful operation 19

plating non-conducting bodies 25

principles of process 17

simple immersion 17

working solutions 23

Electrothermics 2

Enargite 146

Endothermic reactions 1

Eutectic point 120

Eutectoid 120

Exothermic reactions 1

Faraday's laws

Fatigue of metals

Ferrite

Ferro-allojrs

adaptability of elements for

of tungsten

Fire treatment, smelting by

Fireclay

r-'

Index

Fixation of nitrogen

Foundry practice cast iron

expert ability required field of operations tumaces molds

Fuel furnaces

Fuel heating compared with elec- trical heating 51

Fume precipitation, electrical 81

Furnace method of refining cop- per metal 157 practical necessity 157 process 158

Furnaces 109

classification 109

electric 47, 109, 142

in foundries 122

insulating materials and refrac- tory linings 110 open-hearth 131

Fused electrolytes 5, 41

manufacture of aluminum 44

manufacture of sodium products 41

Fused salt 41

G

Galena 163

Gangue 99

Gases, electrical discharge in (See Electrical discharge in gases)

General metallurgy 93

furnaces 109

ores 99

properties of metals 93

Girod furnace 74

Glass, electroplating on 26

Gold, recovery of 14, 15, 91, 175

cyaniding 178

electrolytic refining 179

methods 175

milling and amalgamation 178

placer mining 176

from sea water 15

Gold smelting in connection with

lead 163

Note. — For page numbers see foot of pages.

Page

Page

Graphite

2, 3, 64, 111

as conductor

2,3

as refractory

Graphitization

Gray cast iron

Green-sand molds

H

Hall process of reducing alum- inum 45, 180 Hammering steel 136 Hardness of metals 95 Hearth smelting of lead ore 164 Heat treatment of steel 139

effects of temperature 140

- many factors affecting material 141

ordinary materials 139

Heroult furnace 71, 143

Hydrauhc presses 137

Hydraulicking 176

Hydrogen, electrolytic (see Elec- trolytic hydrogen and oxygen) Hydrometallurgy 89, 146

Hypochlorites, manufacture of 29

chemical action 29

commercial electrolyzers 29

Inactive electrochemical cell 7

Induction steel furnaces 74

Ingots 118, 133

defects of solidification 133

remedying defects 134

specimens 133

Insoluble anodes 12

Insulating materials 110

Ions 8

Iridium 186

Iron and carbon „

eutectic point 120

ferrite 119

other gradations 120

pearlite 120

Iron and steel, metallurgy of

, 15, 69, 112

blast furnace 113

Index

Page lion and steel, metallurgy of (con- tinued) constitution of iron 118

foundry practice 122

manufacture of steel 125

ores of iron 112

wrought iron 1 24

Iron and steel manufacture, elec- tric furnaces in 68, 142 advantages of high temperature 144 arc type of fiunace 70 direct reduction of iron 69 manufacture of crucible steel 70 manufacture of steel from pig

iron 69

pig-iron production 142

status 144

steel production 142

Laboratory sampler 102

Lead 15. 162

ore reduction 164

refining 15, 169

smelting 162

Lead carbonate 163

Lead oxide 163

Iiead silicate 163

lioad sulphate 163

M

Magnesium 184

Magnesium oxide as refractory 111

Malachite 145

Malleability of metals 97

Manganese 186

Malleable iron 124

Martensite structure ' 140

Matting furnace 148

Mechanical roaster 162

Mechanical treatment of steel 135

drawing 139

hammering 136

importance 135

pressing 137

rolling 136

Mercury 183

Mercury cells 33, 35

Note, — For page number see foot of pages.

Page

Metal radical

MetaUic conductors

Metallic silicon as conductor

MetaUic sodium, manufacture by

electrolytic methods

"Metallized" carbon

Metallography

Metallurgical series

Metalltu-gy

general metalliu-gy

introductory

iron and steel

miscellaneous metals

Metals

characteristics

,

electrolytic refining and

recov-

ery of

properties of

crystallization

plasticity

reducibility

strength

Milling and amalgamation

175,

Moebius process of refining silver

Molds in foundries

Molten dipping

Molybdenum

Mond English process of

nickel

smelting

Monel metal

181,

N

Native copper

Negative radical

Nickel

occurrence and use

reduction

Nickel solution

Nitrogen, fixation of

Birkeland-Eyde process

nitrogen for fertilizers

Non-aqueous solutions as

elcctro-

lytic conductors

Non-conductmg bodies,

electro-

plating

plating on glass

rendering surface conductive

Index

Page Non-metallic compounds pro*:

duced in electric furnace 59

alundum 67

calcium carbide 59

carbon bisulphide 67

carborundum 62

graphite -64

silicon products 61

Non-metallic conductors 2

Open-hearth fiunaces ,

122, 131

Opn-hearth steel

furnace

history

process

status

Ores

aluminum

antimony

bismuth

copper

distictions in values

99

economic value of iron

f

mercury

nickel

pretreatment

sampling

tin

tungRten

zinc

Osmondite structure

Oxide copper smelting

process

where used

Oxygen, electrolytic (see Electro- lytic hydrogen and oxy- gen)

Ozone, production of . 77

P

Palladium 185

Parkes' process 169

operation ' 170

principle 169

Pearlite 120

Pearlitic structure 140

Note. — For page numbers see foot of pages.

Page

Pig casting 118

Pig iron

composition of 118

furnaces for 142

manufacture of sted from 69

Piping in steel 133

Placer mining ' 175, 176

Plasticity 97

Platinum 185

Polishing electroplated objects 21; 22

Positive radical 9

Pot roasting of lead ore 165

Precioufil metals, recovery of - 163

Pressing steel , . i37

Pretreatment of ores r 104

iniquetting 108

calcining 105

chemical solution or fusion 108

drying 104

roast-sintering

roasting

sintering 105

Punching method of sampling 103

Pyritic smelting 152

Recovery of metals

1 t

aluminum

electrolytic

gold

17S

Reducibility of metals

9S

Reduction of metals

alloying elements

' copper ores

converting copper matte

methods

oxide copper smelting

reverberatory copper smelting 154

roasting copper ores 152

sulphide copper smelting 148

iron 69

lead 164

hearth smelting 164

lead blast-furnace smelting 166

pot roasting ' 165

reverberatories 164

roast-sintering 165

Index

Page

Page

Reduction of metals (continued)

Silicon carbide (carbonmdum)

magnesium

Silicon products and electric fur-

sodium

nace

timgsten

Silver recovery, electrolytic

zinc

Silver refinery for copper plant

Refining of metals

Silver refining, electrolytic

copper

Silver smelting in connection

electrolytic 12,

with lead

lead

Simple immersion, electroplating

Refractory linings '

by

Regenerative heating

Sintering ores

Resistance furnace 57, 62, 63, 65, 67

Slag

99

Resistor in electric furnace

Smelting of lead

Retorting furnace

lead minerals

Retorts in zinc distillation fur-

relative importance

naces

Sodium

Rverberatory copper smelting

Sodium chloride, deeompositioi

present development

of

Reverberatory furnace 154,

Soluble anodes

Roast-sintering ores 107,

Solutions for deposition of prin*

Roasting copper ores

cipal metals '

field

Sorbite structure

mechanical roaster

Specific resistance

Roasting furnace for zinc ores

Stassano furnace 71,

Roasting ores

Steam thawing

Rolling steel

Steel, manufacture of 69, 125,

Rotating solid core furnace

Bessemer steel

S

carbonizing solid iron

crucible steel

Salt solutions, decomposition of

furnaces for

(see Decomposition of

heat treatment

salt solutions)

ingots

Sampling mill

mechanical treatment

15

Sampling of ores

open-hearth steel

importance

from pig iron

methods

Steel industry, electric furnaces

Schmidt electrolyzer

in (see Iron and steel

Schoop electrolyzer

manufacture, electric fur-

Schuckert electrolyzer

naces in)

Scleroscope

Strength of metals

Segregation in steel

Strong-reduction type of sulphide

Selenium as conductor

copper smelting

Semipyritic type of sulphide re-

Sulphide copper smelting

duction

matting furnace

S iemens-Ualske ozonizer

pyritic type

Silica as refractory

Hi

semipyritic type

Silicon

strong-reduction type

Note. — For page numbera see foot of pagea.

Index

J ' T

rage

Tungsten

rage

Tables

occurrence

chemical composition of fer-

reduction

rous materials

Tt

chemical source of metals

u

comparative reducibility

United States process of nickel

constants of elements

smelting

heat efficiencies of furnaces

physical constants

positive and negative radicals

Vanadium

of the more common

W

compounds

principal iron ores

Water, cells for decomposing

relative fuel costs

Water-cooled metal jackets

variation of combining ele-

Wire drawing steel

ments in pig iron

White cast iron

Tapping type of furnace

White metal

Taylor furnace

Whiting cell

Temperature, effects of on steel

Working solutions for deposition

variation of structure

of principal metals

working limits

Wrought iron

Tempered steels 140,

Z

Tenorite

Tetrajiedrite

Zinc

Tin

characteristics

Titanium

ore reduction

Tonnage production of steel

ores

Towiisend cell

Zinc distillation furnaces

Troostite structure

retorts

N<Ue. — For p<ige numbers see foot of pages.