THE MACMILLAN COMPANY
NEW YORK BOSTON CHICAGO
MACMILLAN & CO., LIMITED
LONDON BOMBAY CALCUTTA
THE MACMILLAN CO. OF CANADA, LTD.
M. DEKAY THOMPSON, PH.D.
ASSISTANT PROFESSOR OF ELECTROCHEMISTRY IN THE
MASSACHUSETTS INSTITUTE OF TECHNOLOGY
THE MACMILLAN COMPANY
All rights reserved
BT THE MACMILLAN COMPANY.
Set up and electrotyped. Published May, 1911. Reprinted
J. 8. Gushing Co. Berwick & Smith Co.
Norwood, Mass., U.S.A.
THE following book was written to supply a need felt by
the author in giving a course of lectures on Applied Electro-
chemistry in the Massachusetts Institute of Technology. There
has been no work in English covering this whole field, and
students had either to rely on notes or refer to the sources
from which this book is compiled. Neither of these methods
of study is satisfactory, for notes cannot be well taken in a
subject where illustrations are as important as they are here ;
and in going to the original sources too much time is required
to sift out the essential part. It is believed that, by collecting
in a single volume the material that would be comprised in
a course aiming to give an account of the most important elec-
trochemical industries, as well as the principal applications of
electrochemistry in the laboratory, it will be possible to teach
the subject much more satisfactorily.
The plan adopted in this book has been to discuss each
subject from the theoretical and from the technical point of
view separately. In the theoretical part a knowledge of theo-
retical chemistry is assumed.
Full references to the original sources have been made, so
that every statement can be easily verified. It is thought that
this will make this volume useful also as a reference book.
An appendix has been added, containing the more important
constants that are needed in electrochemical calculations.
Thanks are due to the following individuals and companies
for permission to reproduce cuts, or to use the material in the
text, or for both: the American Academy of Arts and Sci-
ences ; the American Electrochemical Society ; the Carborun-
dum Company ; Wilhelm Engelmann ; Ferdinand Enke ; the
Electric Storage Battery Company; the Engineering and
Mining Journal; the Faraday Society; the Franklin Insti-
tute ; Charles Griffin and Company ; Gould Storage Battery
Company ; Dr. Eugene Haanel ; the Hanson and Van Winkle
Company; Mr. Carl Hering; Mr. Walter E. Holland of
Thomas A. Edison's Laboratory ; International Acheson
Graphite Company; Wilhelm Knapp; Longmans, Green and
Company ; Progressive Age Publishing Company ; Dr. E. F.
Koeber, Editor of the Metallurgical and Chemical Engineer-
ing ; Julius Springer; Spon and Chamberlain; John Wiley
TABLE OF CONTENTS
COULOMETERS OR VOLTAMETERS 1-12
1. General Discussion 2. The Silver Goniometer 3. The
Copper Goniometer 4. The Water Goniometer 5. The Silver
ELECTROCHEMICAL ANALYSIS 13-29
1. Nonelectrolytic Methods 2. Electrolytic Methods.
ELECTROPLATING, ELECTROTYPING, AND THE PRODUCTION OF ME-
TALLIC OBJECTS 30-42
1. Electroplating: Nickel Plating ; Copper Plating ; Zinc Plat-
ing ; Brass Plating ; Silver Plating ; Gold Plating 2. Gal-
vanoplasty : Electrotyping ; Copper Tubes, Foil, and Wire.
ELECTROLYTIC WINNING AND REFINING OF METALS IN AQUEOUS
1. The Winning of Metals: Copper and Zinc 2. The Elec-
trolytic Refining of Metals: Copper Refining; Nickel Refining;
Silver Refining ; Gold Refining ; Lead Refining ; Zinc Refining.
ELECTROLYTIC REDUCTION AND OXIDATION .... 68-79
1. Reduction 2. Oxidation.
ELECTROLYSIS OF ALKALI CHLORIDES 80-136
1. Theoretical Discussion : The Chemical Action of Chlorine on
Water and Alkali Hydrate; The Electrolysis of Alkali Chloride on
TABLE OF CONTENTS
Smooth Platinum Electrodes without a Diaphragm; The Electrolysis
of Alkali Chlorides with Platinized Platinum Anodes; The Electrol-
ysis of Alkali Chlorides on Carbon Anodes; The Maximum Concen-
trations of Hypochlorite and the Maximum Current and Energy Yields
of Hypochlorite and Chlorate; The Production of Perchlorates ; The
Electrolysis of Alkali Chlorides with a Diaphragm; Decomposition
Points and Potentials of Alkali Chloride Solutions; Fluorides,
Bromides, and Iodides 2. Technical Cells for Hypochlorite,
Chlorate, Hydrate, and Chlorine.
THE ELECTROLYSIS OF WATER 137-141
PRIMARY CELLS . 142-151
THE LEAD STORAGE BATTERY 152-172
1. History and Construction 2. Theory of the Lead Storage
THE EDISON STORAGE BATTERY 173-184
1. General Discussion 2. Theory of the Edison Storage
THE ELECTRIC FURNACE 185-201
1. General Discussion 2. Electric Furnace Design.
PRODUCTS OF THE RESISTANCE AND ARC FURNACE . . . 202-238
1. Calcium Carbide 2. Carborundum 3. Siloxicon 4. Sili-
con 5. Graphite 6. Carbon Bisulphide 7. Phosphorus
8. Alundum 9. Aluminum 10. Sodium and Potassium
TABLE OF CONTENTS IX
THE ELECTROMETALLURGY OF IRON AND STEEL . . . 239-264
1. General Discussion 2. The Electrothermic Reduction of
Iron Ores 3. The Electrothermic Refining of Steel.
THE FIXATION OF ATMOSPHERIC NITROGEN .... 265-287
1. Introduction 2. Absorption by Calcium Carbide 3. The
Oxidation of Nitrogen 4. The Synthesis of Ammonia 5. Con-
THE PRODUCTION OF OZONE 288-314
1. General Discussion : The Maximum Concentration; Yield per
Coulomb for Negative Point Electrode ; Yield per Coulomb for Posi-
tive Point Electrode ; Yield per Kilowatt Hour for Positive and for
Negative Points; Theory of Ozone Formation by Silent Discharge;
The Siemens Ozonizer 2. The Technical Production of Ozone.
Atomic Weights Electrochemical Equivalents Numerical
Relation between Various Units Legal Electrical Units.
NAME INDEX 323-325
SUBJECT INDEX 327-329
LIST OF ABBREVIATIONS
Ann. d. Phys Annalen der Physik.
Ann. d. Chem. und Pharm. . . Annalen der Chemie und Pharmacie.
Ann. d. Chim. et de Physique . Annales de Chimie et de Physique.
B. B Berichte der Deutschen Chemischen Gesell-
Berg- und Hiittenm. Ztg. . . Berg- und Hiittenmanische Zeitung.
Chem. News Chemical News.
Chem. Zeitung Chemiker Zeitung.
C. R Comptes Rendus des Seances de 1'Academie
Dingler's polyt. J Dingler's Polytechnisches Journal.
Electrochem. and Met. Ind. . Electrochemical and Metallurgical In-
Electroch. Ind. Electrochemical Industry.
Elektrotech. Z Elektrotechnische Zeitschrift.
El. World Electrical World.
Eng. and Min. J Engineering and Mining Journal.
Gilbert's Ann Gilbert's Annalen.
J. f. prakt. Ch Journal fur praktische Chemie.
Journ. of the Franklin Inst. . Journal of the Franklin Institute.
J. Am. Chem. Soc Journal of the American Chemical Society.
Met. and Chem. Eng Metallurgical and Chemical Engineering.
Min. Ind Mineral Industry.
Phil. Mag Philosophical Magazine.
Phil. Trans Philosophical Transactions.
Phys. Rev Physical Review.
Pogg. Ann Poggendorff's Annalen.
Proc. Am. Acad Proceedings of the American Academy of
Arts and Sciences.
Proc. Am. Phil. Soc. .... Proceedings American Philosophical So-
Proc. Royal Soc. of Edinburgh Proceedings of the Royal Society of Edin.
Proc. Soc. Arts Proceedings of the Society of Arts, Boston.
Trans. Am. Electrochem. Soc. . Transactions of American Electrochemical
Z. f. anal. Ch Zeitschrift fur analytische Chemie.
Xii LIST OF ABBREVIATIONS
Z. f. angew. Ch Zeitschrift fiir angewandte Chemie.
Z. f. anorg. Ch Zeitschrift fiir anorganische Cheraie.
Z. f. Berg-, Hiittenm.- und Salinen-Wesen. Zeitschrift fiir das Berg-, Hut-
tenmanische- und Salinen-Wesen in
Z. f. Elektroch Zeitschrift fiir Elektrochemie.
Z. f. phys. Ch Zeitschrift fiir physikalische Chemie.
COULOMETERS 1 OR VOLTAMETERS
1. GENERAL DISCUSSION
AN important application of electrolysis is the determination
of the amount of electricity passing through a circuit in a given
time. According to Faraday's laws, (1) the magnitude of the
chemical effects produced in a circuit is proportional to the
quantity of electricity that passes through the circuit, and (2)
the quantities of the different substances which separate at
electrodes throughout the circuit are directly proportional to
their equivalent weights. 2 The first statement is true under all
conditions, but the second only for the case that a single sub-
stance is liberated on any given electrode. If several sub-
stances are deposited together on the same electrode, there is,
of course, less of each than if only one is deposited.
The electrochemical constant, or the quantity of electricity
necessary to deposit one equivalent weight of any substance,
has been accurately determined by measuring the amount of
silver deposited for a known quantity of electricity. The
value of this constant generally accepted is 96,540 coulombs,
and is accurate to a few hundredths of a per cent. 3
1 This name was proposed by T. W. Richards, Proc. Am. Acad. 37, 415, (1902).
2 Le Blanc, Electrochemistry, English translation, p. 42, (1907).
3 Nernst, Theoretische Chemie, 6th ed., p. 716, (1909) ; Guthe, Bulletin of the
Bureau of Standards, 1, 362, (1905).
"* ALLIED.. ELECTROCHEMISTRY
It is evident from the above that the amount of electricity
passing through a circuit can be determined from the amount
of chemical change produced at any electrode if this chemical
change can be measured. There are three general methods of
making this measurement : (1) by weighing the substance de-
posited or liberated, (2) by measuring its volume, and (3) by
titration. It seems hardly necessary to call attention to the
fact that in any coulometer the current can be computed from
the quantity of electricity that has passed through the circuit,
if the current has been constant and if the time is measured.
Current in amperes equals quantity in coulombs divided by
time in seconds.
The errors of coulometers are those inherent in the measure-
ment of weight and volume or in titration, and also those due
to imperfections in the coulometer itself. The latter may
come from a variety of causes, such as the liberation of other
substances than the one assumed, or the loss of the substance
after deposition and before weighing. The errors of each
coulometer described below will be pointed out.
2. THE SILVER COULOMETER
The silver coulometer is the most accurate of all electro-
chemical coulometers. It is for this reason that it is used to
determine the electrochemical constant. It consists of a plati-
num dish cathode, a neutral silver nitrate solution made by
dissolving 20 to 40 grams of nitrate in 100 grams of distilled
water, and a pure silver anode. By weighing the platinum
dish before and after the current has passed, the amount of
electricity may be computed from the value of the electro-
chemical equivalent of silver given above. To obtain the best
results, the anode should be wrapped in filter paper, 1 in order to
prevent any silver mechanically detached from the anode from
falling into the platinum dish, or contained in a porous cup,
which also separates the anode solution from the cathode. The
solution from the anode would deposit too much silver on the
1 Richards, Collins, and Heimrod, Proc. Am. Acad. 35, 143, (1899).
COULOMETERS OR VOLTAMETERS
cathode, due to the formation of a complex silver ion, prob-
ably Ag + , which does not break up at once to the normal ion
Ag + and 2 Ag, and which, if deposited, would give too great a
quantity of silver. 2 This is the main source of error, and when
it is excluded, the mean error of one determination is about
0.03 per cent, for a deposit
weighing not less than
half a gram. 3 The cou-
lometer used by Richards,
Collins, and Heimrod is
shown in Figure 1.
The solution of silver
nitrate may be used until
a deposit corresponding to
3 grams of silver from 100
cubic centimeters of solu-
tion has been reached.
The current density must
not exceed 0.2 ampere per
square centimeter on the
anode, or 0.02 ampere per
square centimeter on the
cathode. The silver ni-
trate solution must be
thoroughly washed out
before weighing, until the
wash water gives no test
for silver with hydro-
chloric acid. The dish is
then dried and weighed.
The silver deposit from
the nitrate solution is crystalline, and does not form a smooth
coating, and for this reason there is danger of losing some of
the crystals in washing. Silver can be deposited with a smooth
surface from the double cyanide of silver and potassium, and it
2 Richards and Heimrod, Proc. Am. Acad. 37, 415, (1902).
3 Ostwald-Luther, Hand- und Hiilfsbuch, 3d ed. p. 497, (1910).
FIG. 1. Porous cup coulometer ( actual size)
A, glass hook for supporting anode. , glass ring for
supporting porous cup. O, silver anode. D, porous
cup. E, platinum cathode.
has been found that a coulometer using this liquid, on exclud-
ing oxygen, gives accurate results without the danger of de-
taching any silver in weighing. 4
3. THE COPPER COULOMETER
The copper coulometer consists usually of two sheets of
copper for anodes, with a thin copper sheet hung between
them as cathode, in an acid solution of copper sulphate. It
is not so accurate as the silver coulometer for several reasons.
In the first place, only 0.29 gram copper is deposited to every
gram of silver. This reduces the percentage accuracy of the
weight to about one third of the value it would have for an
equivalent amount of silver. More important than this are
the chemical reactions that tend to change the weight of
copper deposited on the cathode from the correct weight.
The copper cathode dissolves slightly in acid cupric sulphate,
forming cuprous sulphate :
Cu + Cu ++ = 2 Cu + ,
thereby reducing the weight of the cathode. This takes place
to a less extent if oxygen is excluded. On the other hand, in
a neutral solution the plate gains in weight, due to a covering
of cuprous oxide coming from hydrolysis of the cuprous
sulphate. With increasing temperature not only does the
velocity of the above reaction increase, but also the amount
of cuprous ions in equilibrium with cupric ions, and conse-
quently more cuprous ions are deposited. Wherever cuprous
ions are deposited, the weight of copper is too great, as the
electrochemical equivalent of cuprous copper is double that of
The solution generally used in the copper coulometer is that
recommended by Oettel, 1 consisting of 1000 grams of water,
150 grams of crystallized copper sulphate, 50 grams of concen-
* Farup, Z. f. Elektroch. 8, 669, (1902).
1 Chem. Zeitung, 17, 643, and 677.
COULOMETERS OR VOLTAMETERS
FIG. 2. Copper coulometer
6 APPLIED ELECTROCHEMISTRY
trated sulphuric acid, and 50 grams of alcohol. The alcohol
drives back the dissociation of the cupric sulphate, reducing
the concentration of the cupric ions and therefore of the cu-
prous ions in equilibrium with them. 2 For ordinary purposes
the exclusion of air is not necessary. The current density on
the cathode should lie between 2 and 20 milliamperes per
square centimeter. The advantages of the copper over the
silver coulometer are its greater cheapness and the greater
adhesiveness of the deposit on the cathode. The average error
of a single determination is from 0.1 to 0.3 per cent. 3 A
convenient form of the copper coulometer is shown in Fig-
ure 2. The inside dimensions of the glass vessel are approxi-
mately 4.3 centimeters in width, 16 centimeters in height,
and 17 centimeters in length.
4. THE WATER COULOMETER
The water coulometer measures the quantity of electricity
passing through a circuit by the amount of water decomposed
between unattackable electrodes dipping in a solution through
which the current flows. The amount of water decomposed
may be determined by measuring the loss in weight of the
coulometer, by measuring the total volume of gas produced,
or by measuring the volume of either one of the gases
The decomposition of water by the electric current was first
observed by Nicholson and Carlisle l in 1800. In 1854 Bunsen 2
used a water coulometer in which the loss in weight was deter-
mined ; and since then others have devised coulometers on the
same principle. 3 Figure 3 shows a convenient form of the
apparatus, having a drying tube sealed directly to it ; for be-
fore leaving the cell the gases must, of course, be thoroughly
2 Foerster and Seidel, Z. f. anorg. Ch. 14, 135, (1807).
8 Ostwald-Luther, Hand- und Hiilfsbuch, 3d ed. 497, (1910).
1 Gilbert's Ann. 6, 340, (1800).
2 Pogg. Ann. 91, 620, (1854).
8 L. N. Ledingham, Chein. News, 49, 85, (1884).
COULOMETEKS OR VOLTAMETERS
dried so that no water vapor is carried off with them. It is
evident that this instrument cannot give great accuracy on
account of the relatively small change
in weight produced by the passage
of an amount of electricity equal to
the electrochemical constant. In
the case of water the change in
weight is only 9 grams, as com-
pared with 31.2 grams of copper
and 107.9 grams of silver. The
errors inherent in the instrument
itself are due to the formation of
other products than hydrogen and
oxygen. If a solution of sulphuric
acid is used between platinum elec-
trodes, the oxygen liberated on the
anode contains a certain amount of
ozone. 4 Persulphuric acid, H 2 S 2 O 8 ,
and hydrogen peroxide, due to the
oxidation of water by the persul-
phuric acid, are also produced. The
production of persulphuric acid is a
maximum when the concentration of
the solution is between 30 and 50
grams of sulphuric acid to 100
grams of water. 5 For this reason a
10 to 20 per cent solution of sodium
hydrate is often used, in which none
of the above disturbing reactions
The presence of even a small
amount of salt of a metal with two different valences, such as
iron, may cause a very large error. Table 1 shows what the
magnitude of this error is for iron impurities. 6
4 Schonbein, Pogg. Ann. 50, 616, (1840).
6 Franz Richarz, Ann. d. Phys. 24, 183, (18oo); 31, 912, (1887).
e Elbs, Z. f. Elektroch. 7, 261 (1900).
FIG. 3. Water coulometer
IRON CONTENT IN
CURRENT DENSITY PER
Loss IN DETONATING GAS
IN PER CENT
It is to be noticed that this error is diminished by increasing
the current density.
Sulphuric acid of 1.14 specific gravity has been shown by
F. Kohlrausch 7 to give results
as accurate as the measurements
themselves in coulometers
where the total volume of gas
is measured. He simultane-
ously devised a form of coulom-
eter shown in Figure 4. The
glass tube is 4 centimeters in
diameter and is divided into
units of 5 cubic centimeters.
The base contains 500 cubic
centimeters. The anode is
platinum foil, 4 centimeters
long and 1.7 centimeters wide,
placed between two cathodes of
the same size. To refill the
tube it is simply turned upside
down. A thermometer is sealed
in for determining the tempera-
ture of the gas. On account of
the limited volume of this ap-
FIO. 4. Kohlrausch water couiometer paratus, large quantities of elec-
7 Elektrotech. Z. 6, 190, (1885).
COULOMETERS OR VOLTAMETERS
tricity cannot be measured; it is intended for the measurement
of currents between 3 and 30 amperes. The relation between
the volume of gas generated in one second, saturated with
water vapor at the vapor pressure corresponding to a sulphuric
acid solution of specific gravity 1.14, and the current is as
follows: For 20 and a pressure of 72.5 centimeters of mercury,
one ampere in one second produces 0.2 cubic centimeter of gas,
including the water vapor. Therefore, under these conditions
of temperature and pressure, the number of cubic centimeters
of gas generated per second, when multiplied by 5, gives the
current in amperes. The corrections for the volume in thou-
sandths of a cubic centimeter for different temperatures and
pressure are given in Table 2.
Corrections, in Thousandths of a Cubic Centimeter, for Reducing the Volume of Gas
generated in One Second to the Value which, multiplied hy 5, gives the Current.
Specific Gravity of Sulphuric Acid : 1.14
The following example will illustrate the use of this table.
Barometer, 754 millimeters of mercury.
Height of sulphuric acid in tube 112 millimeters of mercury.
Pressure in gas = 754 - -^ = 745.
Temperature of gas : 17. 8.
Volume of gas 198.0 cubic centimeters.
Correction : + 0.038 x 198.0 = 7.5 cubic centimeters.
205.5 cubic centimeters.
Duration of experiment : 39 seconds.
Therefore in one second 5.27 c.c. of gas were generated.
Current = 5.27 x 5 = 26.3 amperes.
> k ._. On comparison with a tangent galvanom-
X^A eter the current indicated
YJU by this coulometer was
found on an average to be
\ per cent low.
In order to avoid correc-
tion for the height of the
solution, the instrument
may be made like a Hem-
pel gas analysis burette, as
shown in Figure 5.
A very convenient form
of water coulometer has
been devised by F. C. G.
Miiller, 8 shown in Figure
6. The whole apparatus
is placed in a water bath,
so that the temperature of
the gas can be determined.
A is the electrolytic cell
filled with barium hydrate,
which does not foam like
sodium or potassium hy-
Fio. 5. Water cou-
F is the gas re- ~~
mi ,, FiG.6. Miiller's water
The three-way coulometer
8 Z. f. d. phys. und chem. Unterricht, 14, 140, (1901).
COULOMETERS OR VOLTAMETERS 11
stopcock at the top allows the gas to escape through H when
no measurement is to be made. By turning the stopcock at a
given second, the gas passes into H, which is previously filled
with water to the upper mark. When H is filled with gas,
the stopcock is turned to allow the gas to pass out H and the
time noted. This apparatus can thus be left connected in the
circuit and a measurement made at any time.
The water coulometer may be transformed into a direct read-
ing ammeter by a method first applied in 1868 by F. Guthrie. 9
If the gas is allowed to escape through a small hole, a definite
pressure in the instrument is developed, depending on the cur-
rent and size of the hole. The pressure is measured by a
mercury or water manometer. This same principle has been
rediscovered by J. Joly, 10 Bredig and Hahn, 11 and Job. 12 In
Bredig and Hahn's apparatus the gas escapes through capillary
tubes, and by using a tube with different bores the range of
the instrument is varied. Their apparatus is accurate to
about 5 per cent.
5. THE SILVER TITRATION COULOMETER
The silver titration coulometer of Kistiakowsky l is some-
times convenient where the current does not exceed 0.2 ampere
and where the duration of the experiment does not exceed an
hour. A silver anode is dissolved in a 10 per cent potassium
nitrate solution by the passage of the current, and is then
titrated. In the improved form the silver anode is at the
bottom of a tube 18 to 22 centimeters long, 3.5 centimeters in
diameter at the top, and 1 centimeter at the bottom. The
cathode is of copper and dips in a 7 per cent copper nitrate
solution to which ^ of its volume of a 10 per cent potassium
9 Phil. Mag. 35, 334, (1868).
10 Proc. Royal Dublin Soc. 7, 559, (1892).
11 Z. f. Elektroch. 7, 259, (1901).
12 Z. f. Elektroch. 7, 421, (1901).
i Z. f. Elektroch. 12, 713, (1906).
nitrate solution has been added. This solution
is contained in a porous cup at the top of the
tube. After the experiment the potassium
nitrate solution containing the dissolved sil-
ver is drawn off and titrated with 0.02 normal
potassium thiosulphate, and a saturated iron
alum solution as indicator. The error of a
single determination may amount to 0.5 per
In the original form, which is the one still
generally used, the cathode is of platinum and
dips into a J to ^ normal solution of nitric acid.
The division between the acid and the nitrate
is shown in Figure 7 by the dotted line. In
order to have the silver dissolve with 100 per
cent efficiency, it should be freshly deposited
electrolytically ; 2 also, all of the anode should
be the same distance from the cathode, as shown
in the figure ; otherwise the current density will
be too great on the part nearest the cathode, and
bubbles of gas may be given off. It is conven-
ient to have the anode made of a platinum spiral
of the form shown, on which a little more silver
is deposited electrolytically before a measure-
be dissolved off in the measure-
tion coulometer ment.
F ^S: ment than
2 Ostwald-Luther, Hand- und Hiilfsbuch, 3d ed. p. 600, (1910).
1. NONELECTROLYTIC METHODS
THERE are four different electrical methods of quantitative
analysis. These are (1) potential measurements, which give a
means of determining the concentrations of ions too dilute to
determine gravimetrically ; (2) conductivity measurements,
which is a method very convenient for determining concentra-
tions of solutions; (3) titration with a galvanometer in place
of an ordinary indicator, and finally (4) the ordinary electro-
analysis, in which the metal is deposited on a platinum electrode
The principle of the first method, originally pointed out by
Ostwald, 1 is as follows : Suppose the concentration of silver
chloride in its saturated solution is desired. If the electro-
motive force of the cell
Ag | T V NAgN0 3 1 T V NKN0 3 1 saturated solution of AgCl | Ag
were measured, and the concentration ^ of the silver ions in
the nitrate were known, as it is from conductivity measure-
ments, the concentration c z of the silver chloride ions could be
computed by the Nernst formula
In practice some conducting salt is added to the silver chloride
solution in order to lower the resistance of the cell. If potas-
i Lehrbuch, 2d ed. II, 879.
14 APPLIED ELECTROCHEMISTRY
sium chloride is chosen, the solubility of silver chloride is
reduced, but its value in pure water can be computed from this
result. 2 If potassium nitrate were used, no reduction in the
solubility would take place. Where the concentration of the
salt is so small, the ion concentration is very nearly equal to
the total concentration on account of the fact that the salt is
nearly 100 per cent dissociated. Other instances where this
method of measuring ion concentrations has been found use-
ful are in the determination of the solubility of mercurous
chloride from the electromotive force of the cell :
Hg | Hg.CI, in T V NKC1 1 T V NHg 2 N 2 O 6 + HNO 3 1 Hg,
and from this result the solubility of mercurous sulphate from
the electromotive force of the cell, 3
These examples are sufficient to illustrate the method. Some
of the errors that attend these measurements may now be men-
tioned. One difficult}'' is to get different electrodes of the
same metal to show exactly the same electromotive force when
placed in the same solution of one of their salts. This seems to
depend on the surface of the metal, and some method has to be
used to make them as nearly identical as possible. This can
often be accomplished by using an electrode covered electrolyti-
cally with a layer of the metal, or if the metal is more electro-
positive than mercury, amalgams of equal concentrations may
be used. 4 The electrolytic solution pressure is thereby some-
what changed, but by the same amount for each electrode, and
since the electrolytic solution pressure drops out, the resulting
electromotive force is unaffected. Another method of obtaining
constant results is to use the metal in a finely divided form.
This may be done by depositing electrolytically with a high-
current density or by decomposing some compound of the metal
a Goodwin, Z. f. phys. Ch. 13, 641, (1894).
Wilsmore, Z. f. phys. Ch. 35, 20, (1900).
4 Goodwin, I.e. p. 676.
ELECTROCHEMICAL ANALYSIS 15
in question. 5 Another source of error is the potential at the
junction of the different solutions, but this can generally be
either calculated or reduced to an insignificant amount by
adding some indifferent salt 6 or by connecting the liquids with
saturated solutions of potassium chloride 7 or ammonium nitrate. 8
A method based on potential measurement has been worked
out for determining the amount of carbonic acid in gases. 9 The
gas bubbles through a solution of bicarbonate, and the result-
ing hydrogen ion concentration of the solution is determined by
potential measurements, from which the partial pressure of the
carbonic acid can be computed.
The principle involved in determining the amount of sub-
stance in a solution by conductivity measurement 10 is the
same as when any other physical property, such as specific
gravity, is used for the purpose ; that is, the relation between
the conductivity and quantity of substance in solution must be
known. These data have already been obtained in a large
number of cases and have been collected by Kohlrausch and Hol-
born. If the solution contains a single electrolyte whose con-
ductivity at given concentrations has already been determined, all
that is necessary is to interpolate graphically or arithmetically
in the table. If, however, there is a maximum conductivity, as
in the case of sulphuric acid, there would be two possible con-
centrations for a given value of the conductivity. It is easy
to tell on which side of the maximum such a solution lies by
diluting a little and redetermining the conductivity. If the
solution were more dilute than corresponds to the maximum
value, further dilution would decrease the conductivity ; if less
dilute, the conductivity would be increased. In case the solu-
tion has a concentration near that of maximum conductivity,
5 Richards and Lewis, Z. f. phys. Ch. 28, 1, (1899) ; also Lewis, J. Am. Chem.
Soc. 28, 158, (1905).
6 Bugarszky, Z. f. anorg. Ch. 14, 150, (1897).
7 Bjerrum, Z. f. phys. Ch. 53, 428, (1905).
8 Gumming, Z. f. Elektroch. 13, 17, (1907).
9 Bodlander, Jahrb. d. Elektroch. 11, 499, (1904).
10 See Kohlrausch and Holborn, Das Leitvermogen der Elektrolyte, p. 124,
16 APPLIED ELECTROCHEMISTRY
where the determination would be inaccurate, it can be diluted
enough to remove it from this point, and the contents of the
new solution determined. From this the concentration in
the original one can be calculated.
This method has been shown to be useful in the determina-
tion of impurities in sugar and of mineral waters. 11 On account
of the fact that the equivalent weights of the impurities likely
to be present in mineral waters vary only within certain limits,
it has been found that the quantity of the impurities can be
estimated with a fair degree of accuracy from conductivity
without analyzing the water to see which of the usual impurities
This method is also useful in the case of mixtures of two
salts when the conductivity of the mixture is the arithmetical
mean of the single conductivities. This is often the case with
nearly related compounds, which are generally difficult to sepa-
rate chemically. For two substances for which this rule holds,
having at equal concentrations the specific conductivities K
and jfiQ, the conductivity of a mixture of the same total concen-
tration would have the conductivitv K = K \P\ + K iP*. By
this means it has been found possible to analyze satisfactorily
mixtures of potassium chloride and bromide, and sulphates of
potassium and rubidium. 12 Conductivity has also been applied
extensively for the determination of the solubility of very
insoluble salts. 10
The use of a galvanometer as an indicator depends for the
end point either on a sharp change in the resistance of the cell
containing the solution titrated or in the change in the electro-
motive force on electrodes dipping in this solution. An example
of the first case is the titration of silver nitrate with a standard
solution of potassium chloride. 13 A measured quantity of a
standard solution of potassium chloride is placed in a beaker
with two silver electrodes. In series with the two electrodes
u Reichert, Z. f. anal. Ch. 28, 1, (1889).
12 Erdmann, B. B. 30, 1175, (1897).
18 Salomon, Z. f. Elektroch. 4, 71, (1898).
ELECTROCHEMICAL ANALYSIS 17
are connected a galvanometer and a source of electromotive
force, which must be less than the decomposition value of the
potassium chloride. On closing the circuit, only a very small
residual current will be detected. On adding a little of the
silver nitrate to the solution, silver chloride is precipitated, and
a certain amount of silver ions, corresponding to the solubility
of the chloride, will be in solution. We now have the cell
Ag | AgCl solution | Ag,
which has no decomposition point, but the quantity of silver is
so small that the large resistance prevents the current from
increasing to any great extent. As nitrate is added, the
quantity of silver in solution changes very little until the last
of the potassium chloride is used up. The first drop of silver
nitrate in excess now increases the silver ions enormously, and
there is a corresponding large increase in current, due to the
reduced resistance of the cell. The following table shows the
sharpness of the change : 13
CUBIC CENTIMETERS OF AoNO 8
The use of a galvanometer as indicator when the electro-
motive force changes suddenly at the end point is illustrated by
the following examples : 14 Suppose two beakers, one containing
a tenth normal solution of mercurous nitrate, the other a definite
quantity of mercurous nitrate solution to be titrated, are con-
nected by a siphon containing tenth normal potassium nitrate.
The bottom of each beaker is covered with a layer of mercury
which makes contact with a platinum wire sealed in the glass.
w Behrend, Z. f. phys. Ch. 11, 482, (1893).
18 APPLIED ELECTROCHEMISTRY
Such a cell would have the electromotive force R T log -l, where
e l is the concentration of the mercury ions in the tenth normal
solution and c z is their concentration in the unknown solution.
If tfj is equal to c 2 , the electromotive force would be zero, but
in general e l and <? 2 would be somewhat different, so that there
would be a reading in a galvanometer connected across the
terminals of the cell. If a standard solution of potassium
chloride is now added from a burette to the unknown solution,
the concentrated <? 2 will be diminished, due to the precipitation
of the mercury, and consequently the electromotive force will
increase. As the end point is approached the change in electro-
motive force for each drop of potassium chloride added will
be greater and greater, because of the larger percentage change
in the concentration. With the drop of chloride which throws
out the last of the mercury, the percentage change will be the
greatest of all, and there will be a corresponding change in
the reading of the galvanometer. The quantity of mercury ions
now in the solution is due to the solubility of the mercunr
chloride. Since this solubility is diminished by adding a salt
with a common ion, the electromotive force will continue to
increase slowly on adding more chloride, but no further sudden
change will occur. This change then indicates the end point.
It is evident that this method would serve equally well to
determine the strength of the chloride and that the titration can
be carried out, starting with potassium chloride in one beaker in
place of mercury nitrate. In this case there would be a decrease
in voltage at the end point instead of an increase. Bromides
can be titrated as well as chlorides, but a sharp end point is not
obtained with iodides.
Since the determination of the end point depends on the
concentration of the ions, the final volume of the solution must
be kept within such limits that a drop of the solution from the
burette will cause a marked change in the galvanometer read-
ing. Starting with tenth normal solutions, for this reason the
final volume should not exceed 30 cubic centimeters, and
therefore not over 10 cubic centimeters of the unknown
solution should be taken for analysis. Since the end point
can be obtained only to 0.05 cubic centimeter, this means an
accuracy of 0.5 per cent. In titrating potassium chloride the
change in voltage at the end point is from 0.1 to 0.15 volt; in
the case of the bromide it is 0.2 volt. Silver electrodes and
silver nitrate can be used in place of mercury and mercury
nitrates, and by this arrangement it is possible to determine
directly the iodine in the presence of chloride and bromide, if
an ammoniacal solution is used. Silver iodide, unlike silver
chloride and bromide, is nearly insoluble in ammonia. There-
fore on adding silver nitrate to an ammoniacal solution of
potassium chloride, bromide, and iodide, only the silver iodide
will precipitate. When all the silver iodide is precipitated,
there is a sudden change in the galvanometer reading. On
acidifying, the combined amount of chloride and bromide may
be determined. If also the total quantity of silver chloride,
bromide, and iodide is weighed, the original amount of potas-
sium chloride, bromide, and iodide can be calculated. This
procedure, however, is not very accurate for the chloride and
bromide, as is shown by the following analyses. 14
An exactly similar method has been shown to be useful in
the titration of acids and bases. 15 Neglecting the small poten-
tials due to the liquid-liquid junctions, the electromotive force
of the cell
is given by the equation
cone. <? 2
W. Bottger, Z. f. phys. Ch. 24, 253, (1898).
20 APPLIED ELECTROCHEMISTRY
assuming complete dissociation. If alkali is now added to
one of these acids, the hydrogen ion concentration diminishes,
causing a gradual increase in the electromotive force. As in
the cases described above, there will be a sudden change in the
galvanometer reading when the end point is reached. The
hydrogen electrode is shown in Figure 8, and consists of palla-
dium-plated gold, which gives more constant val-
OrV ues than platinized platinum. The concentration
(f of the hydrogen soon becomes constant in the
electrode, as it is not absorbed by the gold at all.
In place of a hydrogen electrode as standard in
the above cell, a normal electrode would do
In carrying out a titration, the acid or alkali to
be titrated is placed in a beaker and the hydrogen
electrode put in position so that the palladium -
plated gold is partly immersed. This electrode
is then connected with the standard electrode and
with some means for measuring the electromotive
force; for example, a Lippmann electrometer and
slide wire bridge. Hydrogen is then bubbled
F gen 8 eilcu-ode" over tne hydrogen electrode till a constant poten-
tial is reached, which should require only a few
minutes, and then alkali or acid, as the case may be, is added
from the burette. After each addition the liquid is stirred up
and the potential measured. This will be found to increase
gradually till the end point is reached, where there will be a
sudden change in the potential.
2. ELECTROLYTIC METHODS
The methods of analysis described above have not come into
general use. The electrolytic method, on the contrary, is ex-
tensively employed, and in some cases has entirely displaced
other methods. It consists in depositing by electrolysis the
substance to be determined on one of the electrodes in a form
that can be dried and accurately weighed. A number of
different cases may be distinguished. A metal is usually
deposited on the cathode in the pure state or in a mercury
cathode as an amalgam. Lead and manganese are exceptional
in that they are deposited on the anode as peroxide. By the
use of a silver anode, chlorine, bromine, and iodine may be
obtained and weighed as the chloride, bromide, and iodide of
silver, though such determinations are not often carried out.
The possibility of electroanalysis was first pointed out by
Cruikshank in 1801. It was very little used, however, until
subsequent to the work of Wolcott Gibbs on the electroanalysis
of copper and nickel in 1864. 1 ' It has since formed the subject
of a great number of investigations and has been employed
extensively in analytical laboratories. A considerable number
of improvements have been made in electroanalytical methods
during this time. One of the greatest of these is the saving of
time by stirring the solution during the electroanalysis, in
place of trusting to electrolytic migration and diffusion to
bring the ions to the electrode on which they are to be
deposited. Table 3 gives an idea of the difference in time
required for analyses with and without stirring. 2
Average Duration of Electroanalysis with and without Stirring
TIME IN MINUTES WITHOUT
TIME IN MINUTES WITH
1 A. Fischer, Elektrolytische Schnellmethoden, p. 11, (1908).
2 A. Fischer, I.e. p. 13.
A second improvement consists in increasing the number of
metals that can be determined electrolytically, by substituting
a mercury for a platinum cathode. Mercury was first sug-
gested for this purpose by Wolcott Gibbs, 3 but not much atten-
tion has been paid to its use until recently. With a mercury
cathode the metal deposited is dissolved by the mercury and is
weighed as an amalgam. E. F. Smith showed that even the
highly electropositive metals belonging to the alkali arid alka-
line earth groups can be determined by this means. 3
In order to explain the theory of electroanalysis, an acid
sulphate solution of some metal standing below hydrogen in
the electromotive series, given in Table 4, will first be con-
sidered. 4 The concentration of the hydrogen ions and metallic
ions is assumed to be one gram ion per liter.
Electrolytic Single Potential Differences between Elements and a Solution contain-
ing one Gram Ion of the Element per Liter. The Normal Electrode on the Scale
Chosen = 0.56 volt
Iron +0.16 5
Cobalt + 0.173 6
Nickel ...... +0.323 6
Tin ...".... <- 0.085
Copper .... -0.606
Arsenic < 0.57
Bismuth <- 0.668
Antimony <- 0.743
Palladium ..... <- 1.066
Platinum < -1.140
Gold <- 1.356
Oxygen ...... -0.670
Suppose two platinum electrodes are dipping in this solution,
and that a gradually increasing electromotive force is applied.
8 E. F. Smith, Electroanalysis, p. 65, (1907).
4 Le Blanc, Electrochemistry, English translation, p. 248, (1907).
6 Calculated from Richards and Behr, Carnegie Institution of Washington,
publication No. 61, p. 31, on the assumption that normal FeSO 4 is 24 per cent
dissociated. e Approximately.
ELECTROCHEMICAL ANALYSIS 23
At first only a small diffusion current will flow, but when the
decomposition voltage of the salt is reached, electrolysis will
begin. The decomposition point is the sum of the potential
differences at the anode and the cathode. Since the sulphate
radical does not escape from the solution, the potential at the
anode will remain nearly constant during the electrolysis, and
the potential at the cathode at the decomposition point is equal
to the potential which the precipitating metal would itself
have in the solution. 7 This will be clear from the following
considerations. 8 Suppose a metallic electrode dips in a solu-
tion of one of its salts in which the osmotic pressure of the
ions of the metal is p. There will be a certain tendency for
the metal to go into solution as ions, called the electrolytic
solution pressure, which will be designated by P. Suppose
that P is less than p, g as must be the case if the metal stands
below hydrogen. A certain amount of the ions of the metal
will then be deposited on the electrode, charging the solution
negatively and the electrode positively. The metallic ions in*
solution will then be repelled by the positively charged elec-
trode with a force &, increasing with the quantity of metal
deposited. This force finally becomes so great that equilib-
rium is established according to the following equation :
The potential difference between the electrode and solution
is then given by the equation
where R is the gas constant, T the absolute temperature, n the
valence of the metal, and F the electrochemical constant. Sup-
pose now the force k is diminished slightly by applying an
external electromotive force in a direction tending to deposit
the metallic ions on the electrode. The value of e will be
7 Le Blanc, Z.c. p. 219.
8 See H. M. Goodwin, Z. f. phys. Ch. 13, 579, (1894).
9 There will be no change in the method of the demonstration if
24 APPLIED ELECTROCHEMISTRY
changed only slightly from that given by the equation above,
but the metal will be deposited continuously, because the sum
of the forces P and k, tending to send the metal in solution,
is now slightly less than the force jt?, tending to cause the
metal to deposit.
As the ions of the metal become more dilute, p becomes less,
and the potential difference e, as well as the decomposition
voltage of the solution, will consequently increase in value.
The potential difference between the solution and the cathode
eventually becomes so great that the value necessary for the
deposition of hydrogen is reached. This potential difference,
e h , is given by the equation
where 77 is the overvoltage of hydrogen on the metal deposit-
ing. After this condition has been reached, the metal and
hydrogen are deposited simultaneously. The following rela-
tion then holds as long as the electrolysis continues :
If electrolysis is continued, the overvoltage 77 gradually in-
creases, due to the increasing proportion of the current used
to liberate hydrogen, 10 and consequently p becomes less. It is
evident that the reduction can never be absolutely complete,
for if p = 0, e would be infinite.
From the equation e = - loef ., it is evident that to
reduce the quantity of metal in solution to a negligible
amount, for example, to j$fa$ ^ ^ ie original quantity,
the increase in voltage at the cathode will be e log 10000
= 0.23 volt for a monivalent metal, or half this value for a
bivalent metal. Monivalent and bivalent metals must there-
fore stand respectively 0.23 volt and 0.12 volt below the
10 F. Foerster, Elektrochemie w&jseriger Losungen, p. 183.
ELECTROCHEMICAL ANALYSIS 25
potential at which hydrogen would be deposited on the metal
in question in order to be so completely separated from the
In consequence of overvoltage and of the possibility of re-
ducing the concentration of hydrogen ions, the potential dif-
ference at which hydrogen is deposited may, under certain
conditions, be very much greater than that given in table of
electrolytic potentials. Consequently, metals standing above
hydrogen in the electrolytic series can be deposited in case the
overvoltage of metal in question is high and the concentration
of the hydrogen ions is low.
It is evident from what has been said that hydrogen plays an
important role in electrolysis. It acts as a safety valve in pre-
venting the potential difference at the cathode from rising
above a certain value. This value depends on the concentra-
tion of the hydrogen ions and on the overvoltage, and it is
therefore possible to vary this maximum voltage by changing
the concentration of the hydrogen ions. For example, the po-
tential difference of a hydrogen electrode in a normal acid solu-
tion differs by 0.81 volt from a hydrogen electrode in a normal
alkali solution. 11 The lower the concentration of the hydrogen
ions, the higher will be the voltage necessary to deposit hydro-
gen, and for this reason solutions of low hydrogen ion concen-
tration must be employed for depositing electropositive metals.
Such solutions are those containing ammonia, ammonium, or
sodium sulphide, and potassium cyanide. In these solutions
the metals form complex salts, and the concentration of their
ions is greatly reduced, and a greater potential difference is
also required to deposit metals from such solutions than from
solutions of their simple salts. Solutions of complex salts are
of great importance in electroanalysis ; some metals, such as
iron, nickel, antimony, and tin, can be reduced quantitatively
only from such solutions. 12
Two metals can in general be separated in an acid solution
when they stand in opposite sides of hydrogen in the electro-
lytic series, for the hydrogen prevents the cathode potential
11 Le Blanc, I.e. p. 209. 12 Fischer, I.e. p. 31.
26 APPLIED ELECTROCHEMISTRY
difference from becoming great enough to deposit the metal
standing above hydrogen. When both metals are below hydro-
gen, they can sometimes be separated by keeping the voltage
below that necessary to deposit the more electropositive metal. 13
As explained above, if the metal to be reduced is monivalent,
FIG. 9. Platinum dish for electroanalysis
the potential difference between it and the solution must be at
least 0.23 volt less than that of the metal from which it is to be
separated, while for a bivalent metal a difference of only 0.12
13 Le Blanc, I.e. p.
volt is necessary. This applies only when the two metals do
not alloy with each other ; if they form an alloy, the decompo-
sition point of each is affected by the presence of the other.
For this reason it is difficult to separate mercury from other
The above theory makes no attempt to explain why some
metals deposit in a compact form and why others do not. This
is a very important question in electroanalysis ; for if the deposit
does not adhere well to the cathode, it cannot be washed and
FIG. 10. Platinum gauze cathode for electroanalysis
weighed. The structure of the deposit depends, first of all, on
the nature of the metal itself. Some metals, such as zinc,
cadmium, and bismuth, have a tendency to deposit in a spongy
form. Others, among which is silver, deposit in large crystals.
The character of the dissolved salt from which a metal is de-
posited is of great influence on the properties of the deposit.
In general, metals are deposited in a compact, smooth layer from
w Fischer, I.e. p. 37.
solutions of a complex salt, which is frequently the only reason
for using them.
The temperature of the solution in electroanalysis is of great
Fio. 11. Mercury cathode for electroanalysis
importance in the case of complex salts. The velocity with
which the ions are produced from the complex is not so rapid
as from the simple salt, but this velocity is increased by an in-
ELECTROCHEMICAL ANALYSIS 29
crease in the temperature. 15 In general, the more complex the
salt, the greater is the effect of high temperature in accelerating
The apparatus 16 commonly used in electroanalysis consists in
a platinum dish cathode 6 centimeters in diameter and 3
centimeters deep. Figure 9 represents such a dish with a
rotating anode. In place of a dish, the cathode may be
platinum gauze. In this case the liquid to be analyzed is held
in a beaker or separatory funnel, as shown in Figure 10. Figure
11 represents an arrangement for using a mercury cathode. A
beaker of 50 cubic centimeters' capacity has a platinum wire
sealed into the bottom by which contact is made with the mer-
cury and the copper plate on which the beaker is placed.
15 Fischer, I.e. p. 34.
16 The illustrations are taken from Edgar F. Smith's Electroanalysis, P.
Blakiston's Son and Company (1907).
ELECTROPLATING, ELECTROTYPING, AND THE PRODUCTION
OF METALLIC OBJECTS
THE object of electroplating is to cover a metal with a layer
of another metal for the purpose of improving its appearance
and durability. The principal metals used for the coating are
nickel, copper, zinc, brass, silver, and gold.
In plating, the first step is to clean the surface thoroughly, in
order to make the deposited coating adhere well. In case the
surface is rough, it must be ground smooth and polished on a
suitable buffing wheel. The next operation is the removal of
the grease and oxide from the surface. The grease is removed
by dipping in a hot solution of sodium hydrate or carbonate.
The alkali is then washed off, and the object is dipped into a
bath called a pickle, the purpose of which is to remove the
oxide and to make it bright. The pickle varies with the metal
to be treated, since a solution which works well with one metal
is not necessarily suited to others. Cast iron and wrought iron
are pickled in a solution made by mixing 1 part by weight of
concentrated sulphuric acid with 15 parts of water. 1 A
suitable pickle for zinc is simply dilute sulphuric or hydrochloric
acid. Copper, brass, bronze, and German silver are treated
with a preliminary pickle consisting of 200 parts by weight of
1 Langbein, Electrodeposition of Metals, 4th ed. p. 162. The English
measures used by Langbein are converted to the metric system when quoted.
Unless otherwise stated, the formulae given for solutions in this chapter are taken
from the above work.
ELECTROPLATING AND ELECTROTYPING
nitric acid of specific gravity 1.33, 1 part of common salt, and
1 of lampblack. The last ingredient has for its purpose the
formation of nitrous acid. After all impurities are removed by
FIG. 12. Plating tank
this bath, the object is washed in boiling water so that on re-
moval it will dry quickly, and it is then immersed in a so-called
bright dipping bath, to give a bright surface. This is made up
of 75 parts by weight of nitric
acid, of specific gravity 1.38,
100 parts of concentrated sul-
phuric acid, and 1 part of
common salt. The object is
then washed off in water and
put while wet in the plating
bath, where all electrical con-
FIG. 13. Tray for plating small
nections should have been
made so that the plating begins
immediately. Instead of the acid pickles following the removal
of grease by alkali, brass is sometimes pickled in a hot solution
of potassium cyanide, which dissolves the oxides, somewhat
32 APPLIED ELECTROCHEMISTRY
more slowly, however, than the acid, but does not alter the
original polish. After the plating is finished, the object is
dipped in hot water and put in warm sawdust to dry.
The tanks used for holding the plating solutions are usually
of wood and are lined with lead or a mixture of pitch, resin,
and linseed oil. The anodes are hung on brass bars running
lengthwise with the tank, and the objects to be plated are hung
on similar bars between two rows of anodes, in order to plate
both sides uniformly. This is illustrated in Figure 12.
Small objects which are to be carefully plated are strung to-
gether in rows on wires and hung in the bath. Where not so
FIG. 14. Drum for holding small objects while plating
much care is required, as in the case of small nails, it is suffi-
cient to place them in a tray, shown in Figure 13, and hang
them in the solution, or in a drum whose sides are perforated,
as in Figure 14. The drum turns on its axle slowly, and the
current is conducted from the pile of small objects to the axle
by metal strips. Of course the tray or the axle and metal
strips are also plated.
When plating is done on a large scale, the current required
ELECTROPLATING AND ELECTROTYPING
34 APPLIED ELECTROCHEMISTRY
is always supplied by a dynamo, but there are the two other
following methods, sometimes used for small jobs, which do not
require a battery or dynamo. If a metal is dipped into a solu-
tion of a salt of a metal standing below it in the electrolytic
series, the more electropositive metal will go in solution and
the more electronegative will be precipitated on the former. A
well-known example of this is the precipitation of copper on
iron, when iron is dipped into solution of copper sulphate.
This is known as plating by dipping. As soon as the metal is
thinly coated, the action, of course, stops. In case the metal is
not electropositive enough to precipitate the one in solution,
the same result can be produced by connecting it with a piece
of zinc placed in the solution. The zinc is dissolved as the
negative pole of a battery and precipitates the metal in solu-
tion on the cathode, which is the metal to be plated. This
method is known as plating by contact. Neither of these
methods is used on a large scale.
Figure 15 shows the plating plant of the National Cash
Register Company, 2 where nickel plating with nickel, copper,
silver, and zinc are all carried out.
Nickel Plating l
Nickel cannot be deposited from a strongly acid bath, since
it is above hydrogen in the electrolytic series. The solution
ordinarily used consists of nickel-ammonium sulphate of the
formula NiSO 4 (NH 4 ) 2 SO 4 6 H 2 O, with an additional amount
of ammonium sulphate to increase the conductivity. The
exact proportions of the salts are not important. Different
receipts are given, varying from 25 to 50 parts of ammonium
sulphate to 50 parts of the double sulphate, in 1000 parts of
water. The solution is made acid enough to redden litmus
paper faintly by adding sulphuric acid, or citric acid, as some
receipts specify. This slight acidity is supposed to give a
2 Met. and Chem. Eng. 8, 275, (1910).
1 For an account of the origin of nickel plating, see Adams, Trans. Am.
Electrochem. Soc. 9, 211, (1906).
ELECTROPLATING AND ELECTROTYPING 35
whiter nickel than alkaline or neutral solutions. Baths of
nickel chloride may be used for plating any metal but iron, for
iron always rusts if plated in a bath of this salt. The anodes
are of cast or rolled nickel.
The proper current density at the cathode is 0.6 ampere per
square decimeter. The whole surface will then be perceptibly
coated with nickel in two or three minutes, and a few bubbles
of gas will come off continuously. If the current is too weak,
the surface becomes discolored. If the current is too strong,
gas is evolved more violently, and the color of the nickel soon
turns dark. In large objects the current density is not uniform.
The more deeply immersed in the solution, the stronger is the
current, so that unless turned during plating, large objects
would receive a thicker coating on the surface that is deepest
in the tank. Iron is sometimes copper plated to prepare it for
nickel plating. This is supposed to make the nickel adhere
better, but nickel adheres perfectly well to iron if the surface
is properly cleaned. 2
The metals usually copper plated, such as zinc, iron, and tin,
are more electropositive than copper. If these are dipped
into a bath of copper sulphate, they are coated immediately
with copper. The copper, however, frequently comes down in
a spongy form that does not adhere well, so that plating from
such a bath is impossible. It is therefore necessary to reduce
the concentration of the copper ions to such an extent that the
copper will be relatively more electropositive than the metal to
be plated, without at the same time reducing the total amount
of copper in the solution. This is accomplished by using
the double cyanide of copper and potassium of the formula
KCu(CN) 2 . The only copper ions present come from the dis-
sociation of the anion Cu(CN) 2 , which is very slight. Copper
will therefore not be precipitated from this solution by zinc or
any other metal that is to be plated. The solution can be made
2 Langbein, I.e. p. 203.
36 APPLIED ELECTROCHEMISTRY
up by dissolving cuprous cyanide in potassium cyanide to form
a 3 to 8 per cent solution, or the double cyanide may be used.
In either case 0.2 per cent potassium cyanide and from J to 1
per cent sodium carbonate is added. 3 The object of the car-
bonate is probabty to increase the conductivity, that of the free
cyanide to dissolve the anodes more readily. In case the
cuprous cyanide is prepared by starting with a cupric salt, the
latter must be reduced to the cuprous state before adding
the cyanide; otherwise poisonous cyanogen would be liberated.
Sodium sulphite is generally used for this purpose. The
copper cyanide bath is heated by a steam coil to 50 to 60 C.
and electrolyzed with such a high current density that there is
a violent evolution of gas. Copper plating is used not only as
a preliminary coating for other metals, but largely also for a
final ornamental covering for iron. Various colors are then
produced on the copper by dipping into a bath of sodium sul-
phide, producing the so-called oxidized copper.
A zinc covering is very useful as a protection for iron. It
has the advantage over tin for this purpose that it is more
electropositive than iron, so that in case a part of the iron
becomes exposed and wet, zinc tends to dissolve in place of the
iron. Iron is covered with zinc by the two methods of electro-
plating and of dipping in a bath of melted zinc. A third method,
called sherardizing, consists in heating objects in zinc dust to
300 C. 1 The zinc deposited electrolytically is not so bright
and pleasing in appearance as the dipped zinc, but it has
been shown to protect the iron much more thoroughly. 2 A
good solution for zinc plating is 200 grams of zinc sulphate,
ZnSO 4 7 H 2 O, 40 grams of sodium sulphate, Na 2 SO 4 - 10 H 2 O,
and 10 grams of zinc chloride per liter, slightly acidified with
sulphuric acid. The current density is from ^ to 2 amperes per
8 Haber, Grundriss der technischen Electrochem. p. 283.
1 Electrochein. and Met. Ind. 5, 187, (1907).
8 Burgess, Electrochem. and Met. Ind. 3, 17, (1905).
ELECTROPLATING AND ELECTROTYPING 37
square decimeter. 3 The anodes are of zinc. Since a little
more zinc dissolves than is deposited, the solution would lose
its acidity unless a small amount of sulphuric acid is added as
it is used up. The resistance may be reduced by warming to
40 or 45 C.
In order to cause copper and zinc to deposit simultaneously,
it is necessary that the metals should be dissolved in a solution
in which a zinc and a copper plate would have potentials nearly
equal. This is the case in a cyanide solution. By replacing
half of the copper cyanide in the bath given above by zinc cya-
nide, a suitable bath for brass plating is obtained. Brass anodes
are used. If a current density of only 0.1 ampere per square
decimeter is used, only a small amount of zinc is deposited with
the copper ; with 0.3 ampere per square decimeter, however, the
deposit contains only 80 per cent of copper. Increasing the
current density changes the composition of the brass only
slightly, though the color becomes greenish. 1
There is quite a large resistance to be overcome in deposit-
ing both copper and zinc from their cyanide solutions, as meas-
ured by the potential difference that must be produced between
the solution and the cathode. This potential difference is
found to be greater than the potential of the metal dipping
into its cyanide solution when no current is flowing, and this
resistance increases with the current density, so that the poten-
tial is soon reached at which hydrogen is deposited on the cop-
per or zinc cathode, in place of the metal. 2
Zinc and copper are deposited together from a solution of
zinc and copper cyanides considerably below the potential of a
pure zinc electrode, which shows electrolytic brass is an alloy
and not a mixture of particles of pure copper and pure zinc. 2
8 Foerster, Elektrochemie wasseriger Lbsungen, p. 255.
1 Foerster, I.e. p. 253.
2 Spitzer, Z. f. Elektroch. 11, 367, (1905).
38 APPLIED ELECTROCHEMISTRY
The double cyanide of potassium and silver is universally
used for silver plating, because of the smooth deposit obtained
from this solution. As stated in Chapter I, silver is deposited
from a nitrate solution in a granular form entirely unsuited for
plating. A solution containing from 1 to 5 per cent silver,
as potassium silver cyanide, KAg(CN) 2 with | per cent of free
potassium cyanide, has been found satisfactory. 1 Too little or
too much free cyanide causes a bad color in the deposit. The
anodes are silver, and the current density on the cathode is
from 0.15 to 0.5 ampere per square decimeter. Silver is de-
posited only on a copper surface. Other metals than copper
or copper alloys which are to be silver plated are first copper
plated. In order to make the silver adhere to this surface it
must be amalgamated before plating. This is accomplished by
dipping into a quicking bath, consisting of a solution of 30
grams of the double cyanide of potassium and mercury,
K 2 Hg(CN) 4 , and 30 grams of potassium cyanide, in one liter
of water. Articles are washed after quicking and placed im-
mediately in the silver-plating bath.
The solution used for gold plating consists of the double
cyanide of gold and potassium, KAu(CN) 2 . This can be pre-
pared by precipitating gold with ammonia in the form of ful-
minating gold, AuNH NH 2 + 3 H 2 O, from a solution of gold
chloride. This is washed and dissolved in potassium cyanide,
and the ammonia boiled off. The concentration of gold varies
between 0.35 and 1 per cent of gold, with twice as much potas-
sium cyanide. 1 The anodes are of gold, and the current density
on the cathode is about 0.2 ampere per square decimeter. Gold
plating is carried out in both hot and cold baths. The metal
deposited from a hot solution is more dense, uniform, and of a
i Haber, I.e. p. 284.
i Haber, I.e. p. 287.
ELECTROPLATING AND ELECTROTYPING 39
Galvanoplasty, or the art of reproducing the forms of objects
by electrodeposition, was discovered by Jacoby of Petersburg
in 1838. It is now used extensively for electrotyping and the
production of copper tubes and of parabolic mirrors.
The first operation in making an exact duplicate of type set
up ready for printing is to take an impression of the type in
wax. The wax sometimes used is ozokerite. The thickness of
the sheet of wax used for the purpose is about half an inch.
After this has been carefully inspected to see that every letter
is perfect, fine graphite powder is well worked into the surface
by soft brushes. This is done in several operations, by machines
and by hand. Copper sulphate is then poured over the surface
and iron powder sprinkled over it to produce a thin layer of
copper, which will make the whole surface more conducting than
the graphite could do. This is an example of the use of plating
by contact, explained above. The sheet is then hung in an acid
copper sulphate bath and electrolyzed for an hour and a half.
It is then removed from the tank, and the wax is warmed and
separated from the thin copper sheet. The copper is next backed
to give it mechanical strength by pouring on it an alloy of lead
and antimony. The subsequent purely mechanical operations
of making the sheet perfectly level, so that each letter will print,
and of mounting them on wood need not be described in this
place. The advantages of electrotyping are the saving of wear
on the type, and the fact that a small stock of type will prepare
unlimited number of pages ; for when once a page is electro-
typed, the type used for preparing this page may be used over
again for another. Nearly all books are now printed in this
Copper Tubes, 1 Foil, and Wire
Tubes are produced by depositing copper evenly on a cylin-
drical cathode, and the copper is removed when it has become
sufficiently thick. In order to keep the outer surface of the
tube smooth, it must be pol-
ished during the electrolysis;
this is done in the Elmore 2
process by means of an agate
wheel whose edge bears on
the tube, as shown in Figure
16. The wheel turns on its
axis and polishes the surface
over which it travels. In
the process of the Societe
des Cuivres de France, the
polishing is obtained by
allowing two tubes to rotate
Agate wheel for polishing tubes
in contact with each other.
Polishing not only keeps the surface smooth, but also makes
the use of higher current densities possible.
The tubes made by the Elmore process are usually 3 meters
long and vary up to 1.6 meters in diameter. 3 In order to sepa-
rate the finished tube from the axle, the surface of the axle
must be specially prepared so as to conduct and yet not make
the contact with the copper deposited too intimate. This may
be done by slightly oxidizing the metal on which the copper is
precipitated. The tube can then be worked loose by pressure.
Numerous patents have been taken out for the production of
copper wire, but only those would be of special interest which
have proved their value in actual use. It is not apparent, how-
ever, from an examination of the literature that any electrolytic
process for making copper wire is in actual use, and the same
1 See Pfannhauser, Die Herstellung von Metallgegenstanden auf Elektro-
lytischem Wege, Engelhardt Monographs, Vol. 6, (1903).
2 Electrochemist and Metallurgist, 3, 151, (1903).
Pfannhauser, I.e. p. 109.
ELECTROPLATING AND ELECTRO-TYPING 41
is true in the case of metal foils. Nevertheless a few of the best
known patents will be described.
In 1891, J. W. Swan patented a method of producing copper
wire, which consists in depositing copper on a wire so as to
thicken it, and in then drawing down the wire to the original
size. The apparatus is so planned that this is a continuous
process. Saunders has patented a method in which the copper
is deposited on a conducting spiral wound on a drum. The
wire is stripped off when sufficiently thick, and is then drawn
For the production of metal foil, Reinfeld's patent calls for
an oxidized nickel cathode. When a thin deposit of metal has
formed, it can be stripped off. The principle of Endruweit's
method is the same. The cathode is a metal ribbon which passes
through an oxidizing solution, then through a bath for clean-
ing, after which the metal foil is deposited upon it.
Besides the production of tubes the only other galvanoplastic
industry which is of importance is the production of parabolic
mirrors. 4 This process has been worked out by Sherard Cow-
per- Coles. It saves the expensive grinding of a parabolic surface
for each mirror, for by this method any number of parabolic mir-
rors can be produced from one mold. The details of the pro-
cess are the following : First a perfectly parabolic glass surface
is prepared by pressing a glass plate about 3 centimeters thick,
and hot enough to be soft, into a cast-iron mold of approxi-
mately a parabolic form. The glass surface which was next
the iron is now made perfectly parabolic by polishing on a
lathe with more refined means as the surface approaches nearer
to perfection. The next step is to clean the surface and cover
it with a thin layer of metallic silver by the ordinary process
used in silvering. The glass form, covered on the parabolic
side with silver, is then placed in a copper sulphate bath, ro-
tated at the rate of five times a minute, and copper plated.
The object of the copper is to give the mirror mechanical
strength. In order to separate the silver and copper from the
glass, they are placed in a water bath and heated to 50 C.
4 See Coles, Engelhardt Monographs, Vol. 14, (1904).
42 APPLIED ELECTROCHEMISTRY
The unequal expansion easily separates the glass from the
metal. The concave side is now a perfect mirror, but the
silver would soon tarnish and must therefore be protected.
For this purpose a thin layer of platinum is deposited on the
silver electrolytically. The solution used for platinizing is
ammonium platinic chloride in sodium citrate. The only pro-
cess that now remains to make the mirror complete is its
mounting, the description of which in this place is unnecessary.
ELECTROLYTIC WINNING AND REFINING OP METALS IN
1. THE WINNING OF METALS
ATTEMPTS have been made to extract metals from their ores
by electrolyzing the ore as an anode, in the hope that it would
dissolve and be deposited at the cathode in the pure state. No
such process has ever been successful, but as failures are in-
structive, the three best known processes for the electrolytic
winning of metals will be briefly described.
An attempt to put the Marchese process in operation is
described by Cohen. 1 The matte from which the copper was
to be won had the following composition:
Copper 17.20 per cent
Lead 23.70 per cent
Iron 29.18 per cent
Sulphur 21.03 per cent
SO 3 0.69 percent
Silica 0.88 per cent
Silver 0.062 per cent
The solution was obtained by treating a matte similar to the
above with dilute sulphuric acid, and consisted principally of
copper and ferrous sulphate. On electrolyzing, copper de-
posits on the cathode and copper and iron are dissolved at the
anode as sulphates. In order to make the oxidizing power of
ferric sulphate available, the matte from which the solution is
i Z. f. Elektroch. 1, 50, (1894).
44 APPLIED ELECTROCHEMISTRY
made is treated with the electrolyte in which ferric sulphate
has accumulated. The ferric sulphate is reduced to ferrous
sulphate, and cuprous sulphide and oxide is changed to copper
sulphate. The solution is then returned to the electrolyzing
Favorable results were obtained in the laboratory in Genoa,
and on a larger scale at Stolberg from February to April, 1885.
The copper obtained was 99.92 per cent pure. A large plant
was then built to produce 500 to 600 kilograms of copper in 24
hours with 58 vats, 2.2 meters long, 1 meter deep, and 1 meter
wide. At first all expectations were realized. The baths
worked well and the copper produced was pure. Within a few
days, however, the voltage across the baths began to rise, in
some cases to 5 volts. This was due to the deposition of sul-
phur on the anode and the disintegration of the anode due to
the dissolving of the copper and iron. Large pieces became
detached from the anode and fell to the bottom of the tank,
filling up the space between anode and cathode and producing
a short circuit. The copper also became impure, containing
antimony, bismuth, lead, iron, zinc, and sulphur. Insoluble
lead electrodes were then tried, but the polarization due to the
formation of lead peroxide was excessive, and the yield in cop-
per fell to 60 per cent of the theoretical amount. The Siemens
and Halske process was then tried by the same company. The
principal difference between this and the Marchese process is
the use of insoluble anodes and the separation of anode and
cathode by a diaphragm. Copper is deposited from a solution
containing ferrous sulphate and copper sulphate. The solution
then circulates to the anode, where ferrous sulphate is oxidized
to the ferric state. The oxidized solution is then used to dis-
solve more copper from the ore. For three months an attempt
was made to carry out this process, but it was finally given up,
partly at least on account of mechanical difficulties, such as the
tearing of the diaphragm and disintegration of the carbon
The Hoepf ner 2 process is similar in principle to the Siemens
2 Z. f. angew. Ch. p. 160, (1891); Chem. Zeitung p. 1906, (1894).
REFINING OF METALS IN AQUEOUS SOLUTIONS 45
and Halske process. The unroasted ore is dissolved by cupric
chloride, and the cupric chloride is reduced to cuprous chloride.
This is kept in solution by sodium chloride. The action of the
cupric chloride is the following : 3
Cu 2 S + 2 CuCl 2 = 4 CuCl + S.
The solution containing cuprous chloride is electrolyzed in
the cathode compartment, where it loses part of its copper. The
solution then circulates to the anode compartment, from which
the cathode compartment is separated by a diaphragm, arid the
remaining copper is oxidized to cupric chloride. The anode
solution is then ready for treating the ore a second time. This
process was also tried on a large scale, but seems to have failed
largely on account of mechanical difficulties, especially with the
The Winning of Zinc
Zinc is one of the few metals in the winning of which elec-
trolysis may take an important part. This is due to the fact
that in the ordinary metallurgical process a loss amounting
sometimes to 25 per cent of the metal occurs. 1 Only under
peculiar circumstances is zinc refined by electrolysis, on account
of the fact that commercial zinc never contains noble metals,
and also because there is not much demand for zinc of a high
degree of purity. 2
In either a refining or a winning process it is of the first
importance to find the conditions under which a smooth deposit
of the metal can be obtained.
Under certain conditions zinc is deposited in a spongy form
that cannot be melted down on account of its tendency to
oxidize. 3 The nature of sponge zinc is still unknown, 4 though
the conditions under which it forms and the ways to avoid it
8 See Blount, Practical Electrochemistry, p. 81, footnote.
1 Foerster, Elektrochemie wasseriger Losungen, p. 289.
2 Giinther, Die Darstellung des Zinks, p. 26.
8 Mylius and Fromm, Z. f. anorg. Ch. 9, 144, (1895).
4 Foerster, I.e. p. 291.
46 APPLIED ELECTROCHEMISTRY
have been the subject of numerous investigations. The factors
which determine the character of the deposit are the tempera-
ture, the current density, the concentration of the solution, and
the impurities present.
From a dilute solution of zinc sulphate, the zinc is always
deposited in a spongy state 6 with a simultaneous evolution of
hydrogen. With a low current density even in a strong solu-
tion the same is true. High temperature, 6 oxidizing agents,
and metals more electronegative than zinc 7 cause the forma-
tion of sponge. A slight acidity tends to prevent the sponge
from forming. 8 Therefore the conditions to obtain zinc in a
compact form are high current density, low temperature, a con-
centrated, slightly acid solution, and the absence from the solu-
tion of oxidizing agents or more electronegative metals than
zinc. As to the limits of current density allowable, different
results have been obtained by different observers. According
to Mylius and Fromm, 9 the current density must be at least
one ampere per square decimeter to prevent the formation of
spongy zinc, while Hasse 10 obtained solid deposits with one
third this density. The strength of the solution is not given.
Kiliani's 11 deposits were spongy at a current density of 2.7 am-
peres per square decimeter, from a zinc sulphate solution of
specific gravity 1.38. Nahnsen seems to have investigated the
condition of deposit with regard to temperature and current
density more systematically than any one else. He obtained
the following results :
6 Kiliani, Berg- und Huttenm. Ztg., 1883, p. 250.
6 Nahnsen, Berg- und Huttenm. Ztg. 1891, p. 393.
7 Mylius and Fromm, I.e. p. 165.
8 Mylius and Fromm, I.e. p. 167.
9 Mylius and Fromm, I.e. p. 169.
10 Z. f. Berg-, Htittenm- und Salinenwesen, 45, 327, (1897).
11 Kiliani, I.e. p. 251.
REFINING OF METALS IN AQUEOUS SOLUTIONS
AMP. PER SQ. METER
In the winning of zinc by electrolysis, the steps are to roast
the ore if it is insoluble, to dissolve the resulting product, and
to deposit the zinc from the solution by electrolysis with in-
soluble anodes. A process devised by Hoepfner to carry out
the winning of zinc in this way was in operation for a while in
Fiirfurth, Germany, and is now in operation in Hruschau,
Austria, and at the works of Brunner, Mond, and Company,
at Winnington, England. 12 The process consists in electrolyz-
ing zinc chloride with carbon anodes, separated by a diaphragm
from the cathode. 13 One great difficulty is to obtain a
diaphragm that will last, and it seems doubtful if this problem
has yet been satisfactorily solved. The chlorine obtained
from the anode compartments is collected and used in making
bleaching powder. 1 *
2. THE ELECTROLYTIC REFINING OF METALS
The object of copper refining is to get as pure a copper as
possible for electric conductors, since a very small amount of
impurity lowers the conductivity materially, 1 and also to ob-
tain the gold, silver, and other impurities.
12 Kershaw, Electrometallurgy, p. 272.
18 For a detailed description see GUnther, I.e.
14 Kershaw, I.e. p. 273. * Addicks, Electrochem. Ind. 1, 580, (1903).
48 APPLIED ELECTROCHEMISTRY
In copper refining, copper anodes containing only a small
percentage of impurities are electrolyzed with the proper
current density in an acid copper sulphate bath of suitable
concentration. The copper and the soluble impurities, which
are not more electronegative than copper, dissolve, while the
insoluble impurities become detached from the anode and fall
to the bottom of the tank, forming what is known as anode
mud or slime. The soluble impurities gradually accumulate
in the solution till purification is necessary. As long as the
impurities are below a certain concentration in the solution, the
copper deposited on the cathode is of much greater purity than
that of the anode. The reason the impurities in solution are
not deposited when dilute is that the voltage drop from solu-
tion to cathode has not reached the decomposition point of
these ions. The decomposition point of an ion changes with
its concentration by the amount ' volt at 17 C., where n
the valence of the metal, for a change in concentration of the
ion in the ratio of one to ten. As the concentration of any
given ion increases, its decomposition point is gradually lowered
until it equals the potential difference between the solution and
the cathode. At this point it is deposited with the copper.
But not all of the impurities found in the cathode are deposited
from the solution. Some are taken up from the slime, of which
a certain amount is always suspended in the solution, on account
of the circulation of the electrolyte. This is true in the case
of silver and gold. 2
It will be interesting next to see what the impurities of
anode copper commonly are, how they behave when the anode
dissolves, and what impurities are deposited on the cathode.
The following table gives a representative composition of
anodes for American refineries :
Copper 98-99.5 per cent
Silver to 300 oz. per ton
Gold to 40 oz. per ton
Arsenic to 2 per cent
2 Addicks, Electrochem. and Met. Ind. 4, 16, (1906).
REFINING OF METALS IN AQUEOUS SOLUTIONS
with small amounts of antimony, bismuth, iron, nickel, sulphur,
selenium, tellurium, and silicon.
A more specific case is given in the following tables, showing
the composition of the anodes and cathodes at the Great Falls
and the Anaconda refineries. 3
COMPOSITION OF ANODES IN PER CENT
Arsenic and antimony .
Oz. gold per ton
For comparison the cathodes are given below.
COMPOSITION OF CATHODES IN PER CENT
Oz. silver per ton
The behavior of these impurities in the anode under the
action of the current was first determined by Kiliani. 4 His
experiments were carried out with a constant current density
on the anode of 20 amperes per square meter and with a solu-
tion of 150 grams of copper sulphate and 50 grams of concen-
trated sulphuric acid per liter. His results will be briefly
recapitulated. Excepting the above statement regarding cur-
rent density and concentrations, his method of experimenting
is not indicated.
Cuprous oxide is not attacked by the current, but goes into
the slime, where it is slowly dissolved, making the bath richer
in copper and poor in sulphuric acid.
8 H. O. Hofman, Electrochem. Ind. 1, 416, (1903).
4 Berg- und Huttenm. Ztg. 1885, pp. 249, 261, and 273.
50 APPLIED ELECTROCHEMISTRY
Copper sulphide and selenium sulphide go into the slime.
Silver, gold, and platinum go into the slime.
Bismuth and bismuth oxide go partly into the slime and
partly into solution, from which they are precipitated as a basic
Tin goes into solution and precipitates, on standing, as basic
Metallic arsenic goes into solution as arsenic acid. If pres-
ent to less than one per cent in the anode, it goes more rapidly
into the slime. 2
Antimony behaves like tin.
Lead goes into the slime as insoluble sulphate.
Iron, zinc, nickel, and cobalt are dissolved by the current
and remain in solution.
A common composition of the slime is the following: 2
40 per cent silver,
2 per cent gold,
25 per cent copper,
5 per cent selenium and tellurium,
10 per cent arsenic and antimony,
18 per cent lead, silicon, sulphuric acid, etc.
The slimes at Great Falls and Anaconda are the following : 3
18 per cent copper
15,000 oz. of silver per ton
38 oz. of gold per ton
10 per cent copper
18,000 oz. of silver per ton
100 oz. of gold per ton
The large amount of copper in the slime is due to part of the
dissolving in the cuprous state and then breaking up into
cupric ions and finally divided copper according to the
2 Cu+ = Cu+ + + Cu. 5
The slimes are worked up for the gold, silver, copper, and
arsenic. The gold and silver have to be purified, and for this
* Foerster, Z. f. Elektroch. 3, 497, (1907) ; Wohlwill, ibid. 9, 311, (1903).
REFINING OF METALS IN AQUEOUS SOLUTIONS
reason copper refineries sometimes have a plant for silver
The electrolyte used in copper refining consists of a solution
of copper sulphate and sulphuric acid. The quantity of cop-
per sulphate (CuSO 4 + 5 H 2 O) varies between 12 and 20 per
cent, the acid between 4 and 7 per cent. 7 Table 6 gives the
conductivities per centimeter cube of two acid copper sulphate
solutions, one containing approximately the smallest amounts
of salts and acid used, and the other, the largest amounts. 8
CONDUCTANCE OF A SOLUTION CONTAINING
3.75% H 2 S0 4
12.5% CuS0 4 5 H,0
Spc. gr. at 22.2, 1.007
9.2% H,S0 4
18.3%CuS0 4 -5H 2
Spc.gr. at 21.2, 1.199
This shows the limits between which the conductance of a
copper sulphate solution used in copper refining would proba-
bly lie. The actual composition of the baths at Great Falls
and Anaconda are the following :
150 grams sulphuric acid per liter
40 grams copper per liter
170 grains sulphuric acid per liter
42 grams copper per liter
A small amount of hydrochloric acid is also added to prevent
the solution of silver and antimony, as well as to produce a
smoother deposit on the cathode. Where a current density as
low as ten amperes per square foot is employed, as at Anaconda,
6 Easterbrooks, Silver Refining Plant of the Raritan Copper Works, Electro-
chem. and Met. Ind. 6, 277, (1908).
7 Ulke, Die Elektrolytische Raffination des Kupfers, p. 42, (1904).
8 Thompson and Hamilton, Trans. Am. Electroch. Soc. 17, 292, (1910).
the electrolyte can be used for many years without purification, 9
while with a 60 per cent higher value some part must be re-
newed frequently. A foul solution at Great Falls has the fol-
lowing composition : 3
51.80 grams copper per liter,
13.20 grains iron per liter,
14.00 grams arsenic per liter,
0.62 grams antimony per liter,
48.00 grams sulphuric acid per liter.
This shows that the impurities can become fairly concentrated
before purification is necessary.
In those refineries where the electrolyte has to be purified,
the operation of purifying is carried out continuously on a cer-
tain fraction of the total amount of electrolyte. The copper is
separated either by electrolyzing with lead anodes or by crys-
tallizing as copper sulphate.
The circulation of the electrolyte, which is maintained by
arranging the vats as in Figure 17, is an important factor.
With no circulation the solution at the cathode would become
- : -'--' " -^"" ~ ~~ ""*"* ^-1-"-! ? J
FIG. 17. Circulation of electrolyte
too dilute for satisfactory deposition, while with too much cir-
culation the slime would be stirred up and contaminate the
cathode. The higher the current density the higher must be
the rate of circulation. This is illustrated by the fact that
at Great Falls, with tanks 9J feet in length, 2J feet in width,
and 3| feet in depth, where the current density is about 40 am-
peres per square foot, the circulation through a tank is 6 gal-
9 Magnus, Trans. Am. Electrochem. Soc. 4, 77, (1903).
KEFINING OF METALS IN AQUEOUS SOLUTIONS
Ions per minute; while at Anaconda, with tanks 8J feet in
length, 4 feet in width, and 4 feet in depth and a current
density of 10 amperes per square foot, the circulation is 3
gallons per minute. 3 At the Raritan Copper Works the rate
of circulation would empty a tank in 1| hours. 10
There are two different systems of arranging the electrodes
used in refining copper, known as the series and the multiple
systems. In the se-
ries system a num-
ber of copper anodes
are suspended in
the bath at equal
distances apart, and
only the two end
ones are connected
to the dynamo, as
shown in Figure 18.
The current then dissolves copper from the first plate, which is
connected directly to the opposite pole of the dynamo, and
deposits it on the near side of the next plate. The other side
of the second plate
c c c c c
FIG. 18. Series system
FIG. 19. Multiple system
is dissolved and
deposited on the
third, and so on
whole series. In
order to separate
the deposited cop-
per from that
which has not been
dissolved, the sides
facing the positive pole are covered with some conducting
material which allows the refined copper to be stripped off.
Of course in this system the tanks cannot be lined with con-
ducting material, for such a lining would cause a short circuit.
Another difference between these tanks and those of the multi-
10 Addicks, Min. Ind. 9, 270, (1900), and Ulke, I.e. p. 63.
54 APPLIED ELECTROCHEMISTRY
pie system is their greater size. Those at the Nichols Works
in Brooklyn are 16 feet long, 5 feet wide, and 5J feet deep. 11
The anodes are from to f of an inch thick, and are placed
from | to -f$ of an inch apart.
In the multiple system the anodes and cathodes are arranged
alternately, as shown in Figure 19. All the anodes are con-
nected to the positive pole of the dynamo and the cathodes to
the negative pole. The cathodes are thin sheets of electrolytic
copper, made by depositing copper on lead or copper covered
with a conducting material from which the copper can be sepa-
rated. At the Raritan Copper Works 6 the cathodes remain in
the tanks 14 days. At the end of 28 days 13 per cent of the
anodes are still undissolved, but at this stage they are removed
and cast into fresh anodes.
In order to reduce the power required, the temperature of
the baths in practice is between 40 C. and 50 C., though from
some experiments of Bancroft 12 70 C. and a current density
between 3.5 and 3.75 amperes per square decimeter would
seem to be more economical as far as power is concerned.
The voltage between the anode and cathode varies between
0.1 and 0.3 volt, depending on current density, temperature,
distance between anode and cathode. 13 This voltage is used
up partly in overcoming the ohmic resistance of the bath and
partly in overcoming the electromotive force of polarization.
Polarization, of course, varies with the current density and the
rate of circulation, but a representative value is 0.02 volt. 14
The actual cost of refining 98 per cent copper has in recent
years been reduced from $20 to |4 or |5 a ton. This im-
provement is due to the more economical use of power 15 and
the more practical handling of the material. About 24 per
cent of the power is still lost in the contact resistance. 16
11 Ulke, I.e. p. 6 et seq.
12 Trans. Am. Electrochem. Soc. 4, 73, (1903).
i* Ulke, I.e. p. 43.
14 Addicks, Trans. Am. Electrochem. Soc. 7, 62, (1905).
i* Ulke, I.e. p. 3.
i 6 Magnus, Electrochem. Ind. 1, 661, (1903).
REFINING OF METALS IN AQUEOUS SOLUTIONS 55
If nickel is deposited from a cold solution of nickel chloride
or sulphate in a layer more than 0.01 millimeter thick, it has a
great tendency to separate from the underlying metal, but this
difficulty can be overcome by heating the solution from which
the nickel is deposited to 60 or 70. l At this temperature and
with a current density of from 0.01 to 0.02 ampere per square
centimeter, nickel is obtained of such ductility that it can be
rolled. Nickel is more electropositive than hydrogen, and the
overvoltage of hydrogen on nickel is not great. Nickel must
therefore be deposited from a very weakly acid solution.
The Balbach Company at Newark, New Jeresy, was one of
the earliest refiners of nickel, as well as of copper. Nickel was
refined by this company from 1894 to 1900 by a secret process.
The product contained 0.25 per cent iron and a small amount
of cobalt. 2 Another process that was in successful operation
for some time is that of David H. Brown. 3 This was not a re-
fining operation, as it had for its object the separation of nickel
and copper in an ore. The ore contained 2 per cent nickel
and as much copper. Anodes were made consisting of 54.3
per cent copper, 43.08 per cent nickel, and the remainder of
iron and sulphur. They were 75 centimeters in width, 60 in
length, and 2J in thickness. The connections were those of
the multiple system. The tanks were of concrete, 256 centi-
meters long, 85 centimeters wide, and 67| centimeters deep.
Each held 1.534 cubic meters of electrolyte. The circulation
was effected as in copper refining, by overflow from bath to
bath. The solution at one time consisted of 44. 3 grams of copper
per liter as cuprous chloride, 55.6 grams of nickel as nickel chlo-
ride, and 100 grams of sodium chloride, but these concentrations
were subsequently modified. The voltage for 24 baths in series
was 6 to 10 volts and the current 500 amperes. In this stage
copper was deposited in a coherent but not dense form. The
iFoerster, Z. f. Elektroch. 4, 160, (1897).
2 Ulke, Electrochem. Ind. 1, 208, (1903).
3 Haber, Z. f. Elektroch. 9, 392, (1903).
relative amount of copper and nickel in the solution flowing into
the baths was the same as that in the anodes. On leaving the
baths the ratio of copper to nickel was reduced to 1 : 80. Sodium
sulphide was then added to the solution, to precipitate the 1.25 per
cent of copper still remaining. After filtering, the solution was
treated with chlorine to change the iron to chloride, which was
precipitated with sodium hydrate and filtered. As much as pos-
sible of the sodium chloride was then removed by concentrating
the solution by evaporation. The nickel was then obtained by
electrolyzing the hot solution with graphite anodes. The current
yield was 92.5 per cent of the theoretical. The chlorine pro-
duced at the anode was used in another part of the process.
The nickel obtained was of the following average composition:
99.85 per cent nickel, 0.085 per cent iron, 0.014 per cent
copper, and was free from arsenic, sulphur, and silicon.
Up to 1902, 454 kilograms of nickel were produced daily in
Cleveland, when it was discontinued by the International Nickel
Trust, in favor of the Orford * Process with which it formerly
competed. The nickel produced by the latter process has vary-
ing compositions, as the following table of percentage composi-
This is pure enough for anodes in nickel plating and the
manufacture of steel. For other purposes, however, such as
making German silver, a better quality is required, and since
1906 the Orford Copper Company has taken up the electrolytic
refining of nickel. 6 Very little is known about the details of
4 This process depends for the separation on the fact that sodium sulphide
forms double compounds with iron and copper sulphides, which float on the top
of melted nickel sulphide.
6 Electrochem. and Met. Ind. 4, 2tf, (1906).
REFINING OF METALS IN AQUEOUS SOLUTIONS 57
this process. The cathodes are said to be 3 by 4 feet in area
and | inch in thickness, and their purity is 99.5 per cent. The
nickel is deposited from a chloride solution.
Two different cases arise in refining silver : one being the
problem of separating silver and copper in an alloy consisting
mainly of these two metals ; the other, the separation of silver
from relatively small amounts of gold and platinum. From
the relative positions of silver and copper in the electrolytic
series, it is evident that if the attempt were made to separate
these metals by electrolyzing an anode containing approximately
equal amounts of each in a solution which dissolves them both,
more silver would deposit on the cathode than dissolves at the
anode. The copper in solution would therefore become so con-
centrated that its decomposition point would be reduced to a
value equal to that of silver. In carrying out this operation it
is therefore necessary either to find a solvent in which only one
of the metals dissolves, or to precipitate one of them by some
other means. In 1877 to 1878 Wohlwill 1 succeeded in separat-
ing silver and copper at the Norddeutsche Amnerie in alloys
containing as much as 30 per cent of silver. The solution was
copper sulphate, more dilute than is used in refining copper, and
the current density was lower. A sponge rich in silver re-
mained adhering to the anode, which had to be removed me-
chanically, and the copper was deposited at the cathode. Another
method for accomplishing the same result, due to Dietzel 2 and
used at the Gold- und Silber-Scheide Anstalt at Pforzheim, de-
pends on dissolving both copper and silver in a weakly acid solution
of copper nitrate at the anode and carrying this solution im-
mediately into another vessel where the silver is precipitated by
contact with copper. After the silver has been thus completely
removed, the copper nitrate solution is made slightly acid and
enters the electrolyzing vat, where a certain amount of the copper
1 Borchers, Electric Smelting and Refining, 2d English ed. p. 309 et seq.
2 Z. f. Elektroch. 6, 81, (1899-1900).
FIG. 20. The Dietzel apparatus for silver
is deposited as it passes the cathode. The arrangement is shown
in Figure 20, which represents a cross section of the dissolving
vessel. JOT are the rotary cylindrical copper cathodes, coated
with a thin layer of grease or graphite, on which the deposition
of copper takes place. When the copper grows out in the form
of trees, it is knocked off.
The copper cylinders are
suspended on flanged con-
tact rollers, which, when set
in motion, cause the cylin-
ders to rotate. Thus the
shafts and driving mecha-
nism are out of contact with
the solution. P is a loose
bottom for supporting the
material to be treated, #,
and is of hard rubber, cellu-
loid, or glass. The plates
P are provided with plati-
num wires for conducting the current to S. DD are filter
cloths, the object of which is to catch any copper falling from
the cathodes and to prevent any of the anodic silver solution
from rising to the cathode. The desilverized electrolyte is
admitted from above, as shown. A small amount of silver
0.03 per cent is deposited at the cathode with the copper.
The solution contains from 2 to 5 per cent of copper and 0.05
to 0.4 per cent of free nitric acid. The current density is 1.5
amperes per square decimeter (14 amperes per square foot) and
the voltage is from 2| to 3 volts.
The electrolytic separation of silver and gold was first carried
out by Wohlwill in 1871. These experiments were made simply
to reduce silver from the solution obtained by boiling the metal
in sulphuric acid. The electrodes were platinum, and the silver
was deposited in loose, pure crystals. When the silver became
dilute, the current decomposed the hot concentrated sulphuric
acid, separating sulphur. No copper was deposited with the
silver, as copper sulphate is very slightly soluble in hot con-
BE FINING OF METALS IN AQUEOUS SOLUTIONS
centrated sulphuric acid. In 1873 experiments were made
with the same solution, but with anodes of auriferous silver.
Pure silver crystals were obtained on the cathode, to which they
adhered sufficiently well to be removed from the bath. The
anode slime also adhered firmly to the anode. The slime con-
tained all the gold and most of the copper. This process was
in operation for some time, during which 2000 kilograms of
silver were refined. It was given up, however, on account of a
number of practical difficulties, which increased when the pro-
cess was carried out on a larger scale. One objection was the
loss of silver caused by the crystals becoming detached from
the cathode before it could be removed from the bath. These
fell to the bottom of the tank and became mixed with the slime
which also became detached from the anode to a certain extent.
The process now most extensively used for refining silver
electrolytically is due to Moebius. There are two processes
known by this name, the old and the new. The former uses
fixed cathodes, and is in operation at the Deutsche Gold- und
Silber-Scheide Anstalt at
the Pennsylvania Lead
Company's works near
Pittsburg, and at Pinos
Altos, Mexico. 3 The new
process has a rotating
cathode and is in opera-
tion at the Guggenheim
Works at Perth Amboy,
New Jersey. 4
The following descrip-
tion of the plant of the
Deutsche Gold- und Sil-
ber-Scheide Anstalt is condensed from Borchers. The cells
are made by dividing a wooden tank 12 feet long and 2 feet
wide into 7 equal compartments. The anodes and cathodes
FIG. 21. Vertical section of the old Moebius
apparatus for silver refining, showing anode
Min. Ind. 4, 351, (1895).
4 Maynard, Eng. and Min. J. 51, 556, (1891).
are suspended parallel to the ends of the tank, as shown in
Figures 21 and 22. The anodes a are of such width that five
can be hung side by side
across the width of the
cell and are from 6 to 10
millimeters thick. The
cathodes k are thin, rolled
sheets of silver that ex-
tend across the whole cell.
Each contains four cath-
odes and three rows of
anodes. The anodes are
inclosed in filter cloth
bags for collecting the
anode mud. Each cath-
ode has two wooden scrap-
ers 8 on each side to scrape
off the silver, which falls
FIG. 22.- Vertical section of the old Moebius j to t covering the
apparatus for silver refining, showing cathodes J
whole area of each cell.
The bottom of the tray is of filter cloth supported by a wooden
The electrolyte is an acid silver nitrate solution, which soon
takes up copper from the anodes as copper nitrate. The con-
centration of the acid varies from 0.1 per cent to 1 per cent,
and the silver con-
centration amounts K
to about 0.5 per cent.
The copper concen-
tration may be as
high as 4 per cent.
The current density FIG. 23. Longitudinal section of the new Moebius
is largely dependent apparatus for silver refining
on the amount of copper in solution. At first, when not much
copper is present, 3 amperes per square decimeter is allowable,
but when the concentration increases to 4 per cent, the current
density must be reduced to 2 amperes per square decimeter on
REFINING OF METALS IN AQUEOUS SOLUTIONS 61
account of the danger of depositing copper with the silver.
The principle on which the silver is separated from the copper
is explained above under electroanalysis. Every twenty-four
hours the whole apparatus suspended in the bath is raised out
and the silver removed, washed, pressed by hydraulic power,
dried, and melted. The anode slime is removed from the bags
once or twice a week. In the later form, shown in Figure 23,
the tanks are 14 feet 3 inches long, 16 inches wide, and 7 inches
deep. An endless sheet of silver (7, -fa inch thick, moves under
the anodes Gr and carries the deposited silver to one end of the
tank, where it is carried out of the tank by the belt D, and is
scraped off by S. Electrical contact is made by F. The
anodes are separated from the cathode by filter cloth, as in the
The electrolytic refining of gold was first accomplished by
Wohlwill 1 at the Norddeutsche Affinerie in Hamburg. The
process consists in electrolyzing gold anodes in a hot acid solu-
tion of gold chloride. A cyanide solution would not do, be-
cause silver and copper would be deposited with the gold.
Wohlwill found that gold anodes do not dissolve when electro-
lyzed in a solution of gold chloride, AuCl g , or of chloroauric
acid, HAuCl 4 , but that in both cases chlorine is set free. In
the solution of chloroauric acid the chlorine may be mixed
with oxygen when the current density is low or the solution
dilute. In order to have the gold dissolve, there must be some
free chloride present, either hydrochloric acid, which is com-
monly used, or some alkali chloride. At a definite temperature
there is a definite amount of free acid for every current density
that will prevent the evolution of chlorine. The amount of
free acid required decreases with increasing temperature.
With a solution containing 3 per cent of hydrochloric acid and
30 grams of gold per liter, at 70 C., as much as 3000 amperes
per square meter can be used without liberating chlorine, but
in practice as much as 1000 amperes per square meter would
hardly ever be used, for other reasons. In case chlorine ap-
1 Z. f. Elektroch. 4, 379, 402, 421, (1898).
62 APPLIED ELECTROCHEMISTRY
pears at the anode, its evolution can be stopped by adding
hydrochloric acid, or by raising the temperature.
The gold is formed on the cathode in large crystalline de-
posits which adhere in such a way that they can be easily
removed mechanically. The more gold in solution, the more
compact the deposit, while an increase in the current density
has the opposite effect. The impurities coming from the anode
also make the gold deposit more compact. With the largest
current density allowable for the anode, 30 grams of gold per
liter is sufficiently concentrated for precipitating the gold in a
The solution of the gold anode shows a certain similarity to
that of copper anodes, in that a portion of the gold is dissolved
in the monivalent state. This decomposes into trivalent gold
chloride and metallic gold, which latter goes into the slimes.
This reaction does not take place as rapidly as with copper,
however, and the monivalent gold exists through the entire
solution and is even deposited at the cathode, causing an in-
crease in the current yield. The higher the current density,
the greater will be the potential difference between the anode
and the solution, and the larger the proportion of gold that
will be oxidized to the trivalent state. This will make the loss
in weight of the anode more nearly equal to the gain at the
cathode. The following table illustrates this statement. The
solution contained 50 cubic centimeters of concentrated hydro-
chloric acid per liter and was at 65 or 70 C. 2
ANODE Loss PER
CATHODE GAIN PER
AMP. HR. GRM. GOLD
AMP. HR. GRM. GOLD
With 15 amperes per square decimeter more hydrochloric acid
had to be added to prevent the evolution of chlorine.
2 Foerster, Elektrochemie wasseriger Losungen, p. 279.
REFINING OF METALS IN AQUEOUS SOLUTIONS 63
The impurities 3 in the anode may consist of silver, lead,
bismuth, and the platinum metals. Silver is converted to silver
chloride which drops into the slime or is removed mechanically.
Lead is changed to the chloride which dissolves slightly. If
present to any considerable extent, it is precipitated by adding
sulphuric acid to the solution from time to time. The anode
then becomes covered with sulphate, which either drops off
itself or is removed mechanically. Bismuth is changed to
the oxychloride and is also removed from the anode mechani-
cally. Platinum and palladium both dissolve completely, while
the other platinum metals go into the slimes. Platinum can
accumulate in the solution till its concentration becomes twice
that of the gold, without being precipitated at the cathode, but
when the solution contains 5 grams or more of palladium per
liter, traces of this metal are found in the gold cathode. The
platinum and palladium are allowed to accumulate to this ex-
tent and are then recovered. Since only gold is deposited,
while other metals are dissolved, the solution, if left to itself,
would become poor in gold. This therefore has to be made
up by adding gold chloride from time to time.
Besides the platinum metals, the slimes contain one tenth the
weight of the gold in the anodes, due to the decomposition of
aurous chloride, as explained above. The gold obtained is not
infrequently 1000 fine and only in quite exceptional cases is
less than 999.8 fine.
At the mint in Philadelphia * the cells are of white porce-
lain 15 inches long, 11 inches wide, and 8 inches deep. Each
cell contains 12 anodes and 13 cathodes, 1J inches apart, con-
nected in multiple. The anodes are 6 inches long, 3 inches wide,
and | inch thick. The cathodes are fine gold yJ 7 inch thick.
Electrolysis is also used for precipitating the gold from the
very dilute solution obtained in the cyanide process. 5 The an-
odes are iron plates 2 to 3 millimeters thick, covered with filter
8 Z. f. Elektroch. 3, 316, (1897). Extract of the German patent, No. 90,276.
4 Electrochem. Ind. 1, 157, (1903). For the mint at San Francisco, see ibid.
6, 355 and 408, (1908).
6 See Cyanid Progresse zur Godgewinnung, by Uslar and Erlwein, Vol. 7, p. 14,
of the Engelhardt Monographs; also Borchers, Z. f. Elektroch. 7, 191, (1901).
64 APPLIED ELECTROCHEMISTRY
cloth, and the cathodes are of thin lead foil. The solution
used for extraction contains from 0.01 to 0.1 per cent of po-
tassium cyanide. The cells are of iron and are 7 meters long,
1.5 meters wide, and 1 meter deep, divided into several com-
partments. The electrolyte circulates from one compartment
to another. The current density is about 0.5 ampere per square
meter at 2 volts. 5 The gold sticks to the lead cathodes, which
are taken out every month and melted with the gold. In some
places the iron anodes have been replaced by peroxidized lead
and the lead cathodes by tin plate, on which the gold is pre-
cipitated as slime. 6
Lead is an ideal metal to refine electrolytically, on account
of its high electrochemical equivalent and of its relatively high
position in the electrolytic series. Its greater tendency to go
into solution than that of most of the metals occurring in it as
impurities makes it possible to dissolve the lead, leaving the
impurities behind in the metallic state. This avoids contami-
nating the electrolyte, which consequently does not need fre-
quent purification. The principal electrolytic difficulty to
overcome was to obtain the lead in a coherent, compact form,
from a solution that would not be too expensive to use on a
commercial scale. The chloride or sulphate, which are usually
the salts employed for metal refining, cannot be used in the
case of lead on account of their insolubility. The problem has
been solved by A. G. Betts, 1 who found that a solution of
lead fluosilicate with a small quantity of gelatine fulfilled the
requirements. The fluosilicate solution is not the only one
from which a good deposit can be obtained ; but it was selected
on account of its low price as compared with other solutions
giving equally good deposits. 2 The object in refining lead is to
recover the copper, antimony, and bismuth, as well as the gold
Electrochem. Ind. 2, 131, (1904).
1 See Lead Refining by Electrolysis, by A. G. Betts. John Wiley and Sons
(1908). 2 Betts, ibid. p. 17.
REFINING OF METALS IN AQUEOUS SOLUTIONS 65
The solution of lead fluosilicate (PbSiF 6 ) is prepared by
adding white lead or lead carbonate to fluosilicic acid. Fluosi-
licic acid is prepared by allowing a solution of hydrofluoric
acid, made from sulphuric acid and calcium fluoride, to trickle
through a layer of pure sand or broken quartz. Heat is applied
to start the reaction, which then furnishes sufficient heat itself
to maintain the necessary temperature. No precipitate is
formed on adding the lead to the acid unless an excess of lead
is added, 3 and the solution obtained is colorless. The strength
of the solution ordinarily employed in practice is from 6 to 7
grams of lead, and from 12 to 13 grams of SiF 6 per 100 cubic
centimeters. 4 This means about 8 grams of free fluosilicic acid
per 100 cubic centimeters of solution. The gelatine is added
to the solution as a hot strong solution of glue. Enough is
added to make its concentration 0.1 per cent. The temperature
of the electrolyte has been found to have no effect in the
character of the lead deposit. 5 In practice about 30 C. is
maintained by the current itself.
The impurities in the anode may consist of iron, zinc, sulphur,
copper, nickel, tin, antimony, arsenic, bismuth, cadmium, gold,
selenium, and tellurium. Only the zinc, iron, nickel, and tin
would go into solution. The other metals are all below lead in
the electrolytic series and would therefore remain in the anode
slime. Zinc, iron, and nickel are above lead and would therefore
not be precipitated from the solution with lead. Tin, however,
is so near lead in the series that it dissolves and precipitates
with the same facility and can therefore not be separated from
lead electrolytically. It must be removed by poling, before
casting the anodes. When only 0.02 per cent of tin is in the
anode, it is found in the cathode. 6 With this exception, the
impurities are easily prevented from reaching the cathode, even
when present in the anode in large quantities. Pure lead can
be obtained when the anode contains only 65 per cent lead, the
rest being impurities of bismuth, antimony, arsenic, silver, and
8 Betts, I.e. p. 30. See also Senn, Z. f. Elektroch. 11, 230, (1905).
4 Betts, I.e. p. 255. 5 Senn, I.e. Betts, I.e. p. 46.
66 APPLIED ELECTROCHEMISTRY
copper. 7 A low current density, 4 amperes per square foot,
was required with anodes of this composition.
The slime nearly all adheres to the anode and is consequently
easily removed from the bath. Its composition of course
depends on that of the anodes. It has been stated that the
handling of the anode slime has not been satisfactorily settled, 8
and from the large amount of space given to this subject by
Betts in his book, it would seem to be an unusually difficult
problem. The method employed at Trail, British Columbia, by
the Consolidated Mining and Smelting Company of Canada,
consists in treating the slime with sodium sulphide, which
extracts 80 per cent of the antimony and some arsenic. The
antimony is then deposited electrolytically on steel cathodes
using lead anodes.
The cathodes used in lead refining are thin sheets of pure lead.
The current density allowable depends on the purity of the
anodes. As stated above, anodes containing only 65 per cent
lead can be refined if the current density is as low as 4 amperes
per square foot. In practice the anodes are about 98 per cnt
pure, 9 and the current density is from 12 to 16 amperes per
square foot. The analysis of refined lead from Trail shows a
purity of about 99.995 per cent. The average voltage per tank
is from 0.30 to 0.38 volt and the polarization amounts to 0.02
volt. The tanks, made of southern yellow pine, are arranged
in the multiple system. The electrolyte is caused to circulate
by having the difference in the level of two successive tanks
from 2J to 3 inches. Five gallons per minute is a fair amount
of circulation for a 4000 ampere tank.
Lead is refined electrolytically at Trail, British Columbia,
New Castle on Tyne, England, and by the United States Metals
Refining Company at Grasselli, Indiana. The capacity of the
first plant in 1908 was about 80 tons a day, of the third 85 tons.
A detailed description of the plants at Trail and Grasseli will
be found in Betts's treatise, referred to above.
7 Betts, I.e. p. 56. 8 Min. Ind. 15, 545, (1906).
For the following statements, see Betts, I.e. p. 287, Table 110 ; p. 255, Table
91 ; p. 287, Table 108, and p. 189, Table 73.
REFINING OF METALS IN AQUEOUS SOLUTIONS 67
It is possible to refine zinc electrolytically, but commercial
zinc contains no metals that it would pay to recover, and the
demand for very pure zinc is limited.
The only impurities occurring in commercial zinc are iron,
lead, and cadmium. In the slightly acid chloride solution, con-
taining about 56 grams of zinc per liter, with a current density
of 1.8 to 1.9 amperes per square decimeter, zinc can be freed
from its impurities to as great an extent as copper. The analysis
of some refined zinc is as follows : 1
99.955 per cent zinc,
0.036 per cent lead,
0.0012 per cent iron,
0.0080 per cent cadmium.
Though the refining of commercial zinc electrolytically is
seldom carried out, certain alloys of zinc rich in silver, obtained
in other metallurgical processes, have been successfully refined
on a commercial scale at Tarnowitz in Silesia. 2 When lead con-
taining silver is treated with zinc, most of the silver is taken up
by the zinc, forming an alloy which floats on the lead. This
zinc scum, containing the silver, is cast into anodes one centi-
meter thick, weighing from 20 to 30 kilograms, which are
electrolyzed in a solution of zinc sulphate. The composition of
the anodes is the following :
Silver 11.32 per cent
Lead 3.13 per cent
Copper 6.16 per cent
Nickel 0.51 per cent
Iron 0.24 per cent
Zinc 78.64 per cent
Antimony, arsenic, bismuth, traces.
The current density is 80 to 90 amperes per square meter,
requiring 1.25 to 1.45 volts. The purity of the resulting zinc
is not given.
1 Foerster and Gxinther, Z. f. Elektroch. 5, 16, (1898), and 6, 301, (1899).
2 Hasse, Z. f. Berg- Hutten- und Salinenwesen, 45, 322, (1897).
ELECTROLYTIC REDUCTION AND OXIDATION
REDUCTION is a term now applied to several really different
processes. It may mean the loss of a positive electric charge
by an ion, as when ferric ion changes to ferrous, or the acquir-
ing a negative charge, as when chlorine changes to a chlorine
ion, or it may mean the direct addition of hydrogen or the
removal of oxygen from a molecule. All of these different
kinds of reduction may be produced electrolytically by bring-
ing the substances to be reduced in contact with a cathode.
Of course the reduction resulting from the addition of hydro-
gen is dependent on the deposition of hydrogen on the cathode,
which reacts while in the nascent state with the reducible sub-
stance with which it comes in contact. The loss of positive
charge may also be represented as being produced by the
hydrogen liberated on the cathode, while in the nascent state,
as illustrated by the equation :
Fe +++ + H = Fe ++ + H + .
Reduction by acquiring a negative charge is illustrated by the
chlorine electrode, made by saturating a platinum electrode
with chlorine. When chlorine changes from the molecular to
the ionic state on a chlorine electrode, the positive current
flows from the solution to the electrode and molecular chlorine
takes a negative charge :
C1 2 + 2 H = 2 Cl- + 2 H+.
ELECTROLYTIC REDUCTION AND OXIDATION 69
Molecular hydrogen has very little reducing power, and con-
sequently the reducing power of a cathode must be ascribed
to the hydrogen liberated on it while in the nascent state.
According to the mass action law, the reducing power of
nascent hydrogen is proportional to its concentration. The
potential difference between the cathode and the solution is
also dependent on the concentration of the nascent hydrogen,
as can be shown as follows : The potential of the hydrogen
electrode is given by the equation 1
where P Ha is the electrolytic solution pressure, and p n+ the
osmotic pressure, of the hydrogen ions in solution. But P^
= ktp, in which &j is a constant and p is the pressure of the
gaseous hydrogen in contact with the electrode and solution. 2
By Henry's Law, p must be proportional to the concentration
<?i, 2 of the molecular hydrogen in the solution immediately on
the electrode. The concentration of the molecular hydrogen
must in turn be proportional to the square of the concentration
of the nascent hydrogen on the electrode, since the reaction is
2 H = H 2 , and by the mass action law, for equilibrium,
The electrolytic solution pressure is therefore proportional to
the concentration of the nascent hydrogen on the cathode,
since, as explained above,
Obviously, any pf the quantities proportional to P 2 Ha may be
substituted in equation (1). Substituting & 3 <? H ,
which shows that the potential of the cathode is a measure of its
reducing power, since it is determined by the concentration of
1 Le Blanc, Electrochemistry, p. 183, (1907).
2 Le Blanc, Electrochemistry, p. 195, (1907).
the nascent hydrogen, e H , assuming e H+ , the concentration of
hydrogen ions, is constant.
If the cathode potential is to be expressed in terms of the
pressure of the hydrogen gas in contact with it and the solu-
tion, it may be done by transforming equation (1) and substi-
tuting as follows :
These equations give only the numerical value of the poten-
tial difference between the electrode and the solution, and take
no account of which is positively and which is negatively
charged. The charge on any electrode whose potential can be
represented by a formula similar to those above may be either
positive or negative, depending on whether the value of the
fraction following the logarithm sign is greater or less than one.
The two principal advantages of electrolytic reduction, over
that produced by adding some chemical reducing agent, which
must of course be oxidized itself, is that no such oxidized sub-
stance is left in the solution, and that the reducing power of a
cathode can be varied within wide limits and in small steps.
One method of varying the reducing power of the cathode is to
vary the current density on it. The increase in the potential
difference that can be obtained in this way, however, is not
very great. This is shown in Table 7, in which are given the
current densities and the corresponding potentials referred to
the normal hydrogen electrode as zero, of cathodes of different
metals dipping in twice normal sulphuric acid : 3 It will be
8 Tafel, Z. f. phys. Ch. 50, 710, (1906).
ELECTROLYTIC REDUCTION AND OXIDATION 71
seen that the potential difference between electrode and solu-
tion does not increase much with increasing current density,
but that for a given current density it is quite different for
different metals. This is due to what has been called the over-
voltage for the metal in question, which means the excess
voltage necessary to liberate a gas on the metal over that
necessary to liberate it on a reversible electrode. 4 The reduc-
ing power of a cathode can therefore be greatly varied by mak-
ing the cathode of different metals.
This change in reducing power may be made to appear in
much larger numerical values by calculating the number of at-
mospheres to which these higher potentials, due to overvolt-
age, correspond ; that is, by assuming that the higher potentials
are produced by compressing the gaseous hydrogen surround-
ing a reversible electrode, and computing the number of atmos-
pheres pressure that would be necessary to make the potential
difference between electrode and solution some definite amount,
0.1 volt, for example. This can be done by writing the expres-
sion for the electromotive force of the cell :
at 1 atmosphere
Pt + H 2 at
and placing it equal to 0.1 volt. The electromotive force of
this cell by (3) is then :
RT, x 0.058 ,
Solving this equation for x gives 2800 atmospheres. For 0.2
volt the value of x is 8 million atmospheres. This is the mean-
ing of the statement frequently met with, 6 that the pressure
of the hydrogen evolved by electrolysis can be increased to
millions of atmospheres. The values thus calculated, however,
can hardly represent the physical state of the gas evolved on
Another important factor in electrolytic reduction is the
* Le Blanc, Electrochemistry, p. 287, (1907).
* Nernst, Theoretische Chemie, 6th ed. p. 756, (1909).
72 APPLIED ELECTROCHEMISTRY
catalytic effect of the metal composing the cathode. As a
result of this effect a substance may be more easily reduced on
one cathode than another, even though the overpressure is the
same for both cathodes. 6
The electrolytic reduction of galena, or lead sulphide, in a
sulphuric acid solution was carried out for a while on a large
scale at Niagara Falls, but had to be given up eventually
on account of the poisonous effect of the hydrogen sulphide
The galena, which had been ground to pass a 40 to 50 mesh
sieve, was spread in a layer J inch thick and covered with
dilute sulphuric acid. 7 The current density was 30 amperes
per square foot, and the current efficiency was about 66 per
cent. 8 About 97 per cent of the lead sulphide was reduced to
spongy lead, which was washed free of sulphuric acid, and con-
verted into litharge by roasting.
In case the substance to be reduced is in solution, it must be
prevented from coming in contact with the anode, where it
would be oxidized again. This is accomplished by separating
the anode from the cathode compartment by some kind of
diaphragm, such as porous clay, that allows the electrolytic
passage of the current, but which prevents the mechanical
mixture of the liquids in the two compartments. An example
of this kind is the production of chromous sulphate from chromic
sulphate. The solution contains 500 grams of chromic sulphate
in 500 cubic centimeters of concentrated sulphuric acid, and is
electrolyzed on a lead cathode with 0.1 to 0.15 ampere per
square centimeter. The blue-green chromous sulphate deposits
on the cathode, as the solution about the cathode becomes satu-
rated with it. 9
6 Foerster, Elektrochemie wasseriger Losungen; p. 315, (1906).
7 Salom, Trans. Am. Electrochem. Soc. 1, 87, (1902).
8 Salora, Trans. Am. Electrochem. Soc. 4, 101, (1903).
9 Foerster, Elektrochemie wasseriger Losungen, p. 319, (1905).
ELECTROLYTIC REDUCTION AND OXIDATION 73
The oxidizing power of an anode is related to the potential
difference between the electrode and the solution in the same
way as the reducing power of a cathode and the potential dif-
ference between it and the solution. There is also an over-
pressure for oxygen on different metals, as in the case of
hydrogen. 1 The results of the following table were obtained
in a normal solution of potassium hydrate. The potential dif-
ferences given between anode and solution were measured when
oxygen first appeared on the anode against a hydrogen elec-
trode in the same solution.
Potential Difference between Anode and Solution when Oxygen first Appears
The number of metals that can be used as anode is much less
than those that can be used as cathode, and is limited to those
metals that would not be dissolved by an action of the current.
Platinum, lead, and carbon are the principal materials for un-
attackable anodes in acid solutions, while besides these both
nickel and iron may be used in alkaline solutions.
Coehn and Osaka also found a decomposition point of 1.1
volts for all of the metals investigated, which they identified
1 Coehn and Osaka, Z. f. anorg. Ch. 34, 86, (1903).
74 APPLIED ELECTROCHEMISTRY
with the value of the hydrogen-oxygen cell, then thought to be
1.06 volts. The true value of this cell, however, has since been
found to be 1.22 volts, 2 so that their first point cannot have this
significance. The overvoltage of a spongy nickel electrode is
evidently very small, for its value in the above table is only
a little greater than 1.22 volts, the true potential of an oxygen
electrode, assuming a hydrogen electrode in the same solution
equal to zero.
There is also a catalytic effect of the anode material on oxi-
dation, which may be of more practical importance than the
overpressure. For example, the yield in oxidizing iodic to
periodic acid on smooth platinum was found to be 1 per cent,
on platinized platinum 3 per cent, and on lead peroxide 100 per
cent, though the potential differences between the anodes and
the solution were 1.72, 1.48, and 1.52 volts respectively. 3 In
the oxidation of chromium sulphate, described below, smooth
platinum anodes give practically no yield of chromate, while
with lead peroxide anodes current yields between 20 and 97
per cent are obtained, depending on the concentration of the
chromium sulphate, though the overpressure of oxygen on the
peroxide is only a few hundredths of a volt higher than on
The following are some of the most important technical ap-
plications of electrolytic oxidation.
In dye works, solutions of sodium or potassium bichromate
and sulphuric acid are used for oxidizing anthracene to anthra-
,CH, ' CO
H 4 / I
The bichromate is thereby reduced to chromium sulphate and
must be regenerated before it can be used again. Formerly
this was accomplished by precipitating with calcium hydrate
2 Nernst, Z. f. Elektroch. 11, 835, (1905) ; Haber, ibid. 834 ; Lewis, Journ.
Am. Chem. Soc. 28, 185, (1906).
Mtiller, Z. f . Elektroch. 10, 61, and 62, (1904).
* Mtiller and Seller, Z. f. Elektroch. 11, 863, (1905).
ELECTROLYTIC REDUCTION AND OXIDATION 75
and heating the resulting pasty material, consisting of chromium
oxide, calcium hydrate, and calcium sulphate, to red heat.
This treatment produces calcium chromate, which, when treated
with sodium sulphate, gives sodium chromate and calcium sul-
phate. On removing the insoluble calcium sulphate the sodium
chromate can be used for oxidation. This method is uneco-
nomical on account of the loss of sulphuric acid and of chromium
which it involves, and it has been superseded by the electro-
lytic process patented in 1898 by the Farbewerke vorm. Meister,
Lucius, und Brunig. 5 This process consists in oxidizing on a
lead peroxide anode a solution of chromium sulphate contain-
ing free sulphuric acid, in the anode compartment of a lead-
lined electrolytic cell. The anode and cathode compartments
are separated by a diaphragm. The chromium is oxidized from
a cation to an anion in changing from a chromium salt to
a chromate, and at the same time sulphuric acid concentrates
in the anode compartment, due to the migration of the sulphate
ions. After using the anode liquid for oxidation, it is first
placed in the cathode compartment, where the sulphuric acid
concentration decreases, after which it is again oxidized.
It is very difficult to construct diaphragms of size great
enough for technical use that can resist the action of the
chromic acid produced. Le Blanc, 6 after a number of experi-
ments, produced diaphragms consisting of 25 per cent alumina
and 75 per cent silica, which he considered satisfactory at the
time, but it seems eventually not to have been successful, for he
has since patented a process for this oxidation in which the two
compartments are separated by a partition reaching not quite
to the bottom of the cell, in place of a conducting diaphragm. 7
The liquid is circulated from the cathode to the anode com-
Another example of technical oxidation is the production of
insoluble salts and oxides of metal by a process patented in
1894 by C. Luckow. 8 The difficulty encountered in the electro-
6 Z. f. Elektroch. 6, 266, (1899). 6 Z. f. Elektroch. 7, 290, (1905).
7 Z. f. Elektroch. 13, 791, (1907) ; 14, 12, (1908).
8 Borchers, Z. f. Elektroch. 3,482, (1897).
76 APPLIED ELECTROCHEMISTRY
lytic manufacture of insoluble salts or other compounds by the
oxidation of the metallic anode is that the compound sticks to
the anode and produces a high electrical resistance. In the
Luckow process this difficulty is overcome by using a 1^ per
cent solution of a mixture of two salts, the anion of one forming
a soluble salt with the metal of the anode, and the anion of the
other forming the insoluble salt desired. The mixture consists
of 80 parts of the first, or auxiliary salt, to 20 parts of the
second, or principal salt. The anions of the principal salt,
being present in a much smaller number than those of the aux-
iliary salt, are soon used up in the layer of solution next to the
anode, and are replaced slowly because the auxiliary anions
carry most of the current on account of their greater number.
The ions of the anode, on dissolving, do not, therefore, come in
contact with the anions of the principal salt directly on the
anode, but the precipitate is formed a slight distance from the
anode and therefore does not stick, but falls down to the bottom
of the cell. 9
If the auxiliary salt is not added, the salt desired cannot be
produced with a satisfactory yield, for either the anode is
covered with an insulating layer of the insoluble salt, or the
desired salt is not produced at all. For example, in electro-
lyzing a lead anode in a 0.12 per cent solution of potassium
chromate, a mixture of lead peroxide and lead chromate formed
on the anode, but practically no yield of lead chromate could be
obtained. 10 Even when the two salts are in the right propor-
tion, if the solution is too concentrated, the same difficulties are
In manufacturing white lead, for which the Luckow process
seems well suited, a 1J per cent solution of a mixture of 80 per
cent sodium chlorate and 20 per cent sodium carbonate is elec-
trolyzed with a soft lead anode and a hard lead cathode, with a
current density of 0.5 ampere per square decimeter. Carbon
dioxide is passed through the solution over the anode to replace
that removed by the lead. If enough of the gas is passed
Le Blanc and Bindschedler, Z. f. Elektroch. 8, 262, (1902).
loisenburg, Z. f. Elektroch. 9, 275, (1903).
ELECTROLYTIC REDUCTION AND OXIDATION
through the solution, the pure carbonate of lead is produced, and
in order to get basic carbonate the quantity of carbonic acid
must be limited. The same result can be accomplished by
diluting the carbonic acid with an indifferent gas, such as air,
and passing an excess through the solution. Table 9 shows the
relation between the concentration of the gas and the product : 10
EATIO OF AIR TO C0 2 BY
PER CENT PbO IN PRODUCT
PER CENT PbO IN WHITE LEAD
2PbC0 3 .Pb(OH) 2
It is evident that the carbon dioxide is too concentrated when
mixed with air in the proportion of 40 to 60.
In producing oxides by this metal, the mixture of salt elec-
trolyzed contains only 0.5 per cent of the auxiliary salt. For
lead peroxide, a 1J per cent solution of a salt mixture con-
sisting of 99.5 per cent of sodium sulphate and 0.5 per cent of
sodium chlorate, acidified with sulphuric acid, is used. The
current density on the anode is about 0.2 ampere per square
The electrolytic method of producing iodoform has almost
entirely displaced the older chemical method. The electrolytic
method was patented as early as 1884 by the Chemische Fabrik
auf Aktien, vorm. E. Schering. 11 According to this patent,
iodoform is made by electrolyzing a hot solution of potassium
iodide and alcohol, through which carbon dioxide is passed.
The addition of alkali carbonate also was found advantageous,
when the study of this subject was taken up. 11 The final
result of the chemical reaction of iodine on alcohol in the pres-
ence of alkali carbonate is represented by the equation :
C 2 H 5 OH + 10 I + H 2 = CHI 3 + C0 2 + 7 HI.
11 Elbs and Herz, Z. f. Elektroch. 4, 113, (1897).
78 APPLIED ELECTROCHEMISTRY
The iodine may be furnished by liberating it electrolytically
from potassium iodide on a platinum anode. This is an oxida-
tion, since the iodine ion is deprived of a negative charge.
A suitable solution for this electrolysis is made up of 5 grams
of sodium carbonate, 10 grams of potassium iodide, 20 cubic
centimeters of alcohol, and 100 cubic centimeters of water.
The iodine does not act on the alcohol directly, as given by
the above equation, but first forms alkali hypoiodite with the
hydroxyl ions from the hydrolysis of the carbonate according
to the equation :
The hypoiodite is hydrolytically dissociated as follows :
NalO + H 2 = NaOH + HIO.
Hypoiodous acid, being unstable, decomposes in the following
two ways : 12
3HIO = HIO 3 + 2HI
and C 2 H 5 OH + 5 HIO = 2 HI + CHI 3 + CO 2 + 4 H 2 O.
That iodine does not act directly on alcohol was proved by
determining the decomposition point of the solution with and
without the addition of alcohol. If the alcohol combined di-
rectly with the iodine liberated, it would reduce the concen-
tration of the free iodine on the electrode and lower the de-
composition point. Since the potential of an iodine electrode
in which <7 Ia is the concentration of the free iodine and <7j_ is
that of the iodine ions, any substance in solution which reduces
the value of (7 Is will change the numerical value of the potential.
It was found that alcohol has not such depolarizing effect,
but that the carbonate has, which fact points to the explana-
tion given above.
12 Dony-H^nault, Z. f. Elektroch. 7, 67, (1900).
Foerster, Elektrochemie wasseriger Losungen, p. 124, (1906).
ELECTROLYTIC REDUCTION AND OXIDATION 79
A high current density decreases the yield, since a greater
concentration of alkali hypoiodite tends to produce a larger
amount of iodate. With a solution made up of 10 grams of
alcohol, 5 grams of sodium carbonate, 16 grams of potassium
iodide, and 100 grams of water, Foerster and Meves obtained
the following results : 14
AMPERES PER SQUARE DECIMETER
CURRENT YIELD IN PER CENT OP THE
Since iodine is continuously removed from the solution, and car-
bon dioxide is added, the alkali carbonate will increase in con-
centration. When it had increased to six times the amount
given in the formula just above, the yield fell to 43 per cent,
with a current density of 2 amperes per square decimeter, and
the iodoform formed in a thick crust on the anode and con-
tained free iodine. The carbonate should therefore not be
allowed to accumulate to this extent.
Bromoform and chloroform cannot be produced in this way,
but other oxidation products are formed, especially chlor- or
brom- aldehyde. This is due to the higher potential at which
bromine and chlorine are liberated, which is sufficient to oxi-
dize the alcohol. Bromoform can be produced with a good
yield, however, if acetone is used in place of alcohol.
i* Z. f. Elektroch. 4, 268, (1897).
THE ELECTROLYSIS OF ALKALI CHLORIDES
1. THEORETICAL DISCUSSION
The Chemical Action of Chlorine on Water and Alkali Hydrate
THE electrolysis of sodium and potassium chlorides is one of
the largest electrochemical industries that is carried out in
aqueous solution. Chlorine and sodium hydrate, hypochlorite,.
chlorate, or perchlorate may be produced from sodium chloride,
depending on the conditions of the electrolysis.
The first products obtained on electrolyzing the solution
of an alkali chloride are chlorine at the anode and alkali
hydrate at the cathode. If these two primary products are
the ones desired, they must not be allowed to mix, while if
hyperchlorite, chlorate, or perchlorate is desired, the chlorine
and hydrate must be allowed to react with each other. Before
describing the electrolysis of the alkali chlorides, it will be nec-
essary to give a brief account of the purely chemical reactions.
that take place between chlorine and the alkali hydrates, and
between chlorine and pure water.
Chlorine enters into a reaction with pure water to a slight
extent, according to the equilibrium represented by the equa-
tion : 1
C1 2 + H 2 O ^ H+ + Cl- + HOC1. (1)
The equilibrium constant of this reaction is
i Jakowkin, Z. f. phys. Ch. 29, 613, (1899).
ELECTEOLYSIS OF ALKALI CHLORIDES 81
if the concentrations are taken in moles per liter. 2 It is evi-
dent from the large value of this constant, and from the fact
that the concentration of free chlorine in a saturated solution
at 25 is only 0.064 mole per liter, 3 that the concentration of
hydrochloric and hypochlorous acids that can exist together in
solution are very small. If brought together in greater con-
centrations, chlorine will be produced, according to equation
(1), taken from right to left.
If chlorine is passed into a solution of alkali hydrate, the
following reaction between the chlorine and hydroxyl ions
takes place : C1 2 + OH- ^ HOC1 + Cl~ (2)
The value of the equilibrium constant of this equilibrium is
given by the following equation : 4
which is derived from the equations
Cci. K w 1.4 x 10- 14
- -- l2 -- =2570 and C H+ = ^ = ^- -
^H+ * ^Cl- * ^HOCl ^OH- ^'OH-
In all of these equations the concentrations are in moles per
liter. Hypochlorous acid then reacts with the unchanged
hydrate to produce a hypochlorite, and this reaction also
leads to an equilibrium represented by the equation :
HOC1 + OH- ^> OC1- + H 2 O, (4)
for which the equilibrium constant is
C OH _
This is the hydrolysis constant of the hypochlorite. The value
of K 3 can be obtained from the dissociation constant of hypo-
chlorous acid : 6 r r
K = ^oci- ^H+ = 3. 7 x lQ-8,
2 Luther, Z. f. Elektroch. 8, 602, (1902).
3 Foerster, Elektrochemie wasseriger Losungen, p. 341, (1905).
4 Foerster and Miiller, Z. f. Elektroch. 8, 921, (1902). The value of K w is
taken from van Laar, Theoretische Elektrochemie, p. 174, (1907).
6 Sand, Z. f. phys. Ch. 48, 610, (1904).
82 APPLIED ELECTROCHEMISTRY
and the dissociation constant of water:
K W = C H+ COH- = 1.4 X 10-".
Dividing K w by K 4 ,
KW _ CH+ COH- CHOCI _ _ 1.4 X 10~ 14 _. 3 g x
K 4 C OC1 -.C H+ "8.7x10-8
When therefore any quantity of chlorine acts on alkali hydrate,
the resulting quantities of hydrate, chlorine, chloride, hypo-
chlorous acid, and hypochlorite are determined by the equilibria
represented by equations (2) and (4). Only when there are
at least two equivalents of hydrate to one mole of chlorine does
the following reaction hold :
C1 2 + 2 NaOH = NaCl + NaOCl + H 2 O. (5)
This is the sum of equations (2) and (4), and is the one usually
given to represent the reaction between chlorine and hydrate.
Since the equilibria represented by equation (3) and the equa-
tion for the value of K 3 exist simultaneously, the values of C OII _
and CHOCI are the same in both. From the equation for K 3 ,
CHOCI _ vr C OC1 _
P 3 * 77 2
^OH- *-* OH-
and combining this with the equation for K 2 ,
^Cl- ^OH- ^ OH-
This equation is convenient for predicting what effect a change
in the concentration of one substance will have on that of the
From equation (6) it would seem that for a given value of
C cla and C C1 _, the value of C OC1 _ could be increased in propor-
tion to the value of C OH _. This would be true, if the concen-
tration of the hypochlorite, C OC1 _, were not limited by another
reaction, the oxidation of hypochlorite to chlorate by hypo-
chlorous acid, according to the equation : 6
2 HOC1 + QC1- = ClOg + 2 Cl- + 2 H+. (7)
Foerster and Jorre, J. f . prakt. Ch. 59, 53, (1899) ; Foerster, ibid. 63, 141,
ELECTROLYSIS OF ALKALI CHLORIDES 83
The free hydrochloric acid then sets free an equivalent amount
of hypochlorous acid according to the equation :
2 H + + 2 Cl- + 2 OC1- = 2 HOC1 + 2 Cl~, (8)
and the hypochlorous acid thus set free oxidizes more hypo-
chlorite. This process continues until all of the hypochlorite
has been changed to chlorate.
Substituting the numerical values of K 2 and K 3 in (6), we
1.4 xlO-tto^- (9)
In order to illustrate the use of the above equation, the rela-
tive concentrations of chlorine ions, hydroxyl ions, free chlorine,
and hypochlorous acid in a neutral solution normal with respect
to hypochlorite ions will be calculated. From the value of K 3 ,
the values of C HOC1 and C OH _ are each 6.2 10~ 4 mole per liter,
and from (9) the value of the fraction ^- is 3.6 x lO' 11 . If
the concentration of chlorine ions is also normal, that of the
free chlorine is only 3.6 x 10~ n mole per liter. 4
If chlorine is led into a solution of alkali hydrate, nothing
but hypochlorite and chloride are produced as long as some of
the hydrate remains unneutralized. This is because the excess
of hydroxyl ions drives back the hydrolysis of the hypochlorite
and therefore prevents the formation of a free hypochlorous
acid. When an amount of chlorine equivalent to the hydrate
has been added, there is still so small a quantity of free hypo-
chlorous acid present that the solution is fairly stable. An
excess of chlorine, however, increases the concentration of the
free hypochlorous acid to such an extent that the hypochlorite
is rapidly oxidized to chlorate, according to equation (7). The
fact that an excess of chlorine was necessary to produce chlo-
rate was first discovered by Gay-Lussac. 7 The addition of a
small quantity of free acid would have the same effect as an
excess of chlorine, for it would set free hypochlorous acid.
7 Liebig Ann. 43, 153, (1842).
84 APPLIED ELECTROCHEMISTRY
If chlorate were formed only by means of free hypochlorous
acid, hypochlorite would be more stable the greater the excess
of hydroxyl ions in the solution. Chlorate is produced, how-
ever, slowly in alkaline solutions, presumably by the reaction
3 NaOCl = NaClO 3 + 2 NaCl. (10)
Hypochlorous acid breaks up in exactly the same way, when it
decomposes of itself. The solution has to be heated to 70 C. to
make this reaction proceed with an appreciable velocity, 6 and
it is also catalyzed by light. With increasing alkalinity the
velocity of the reaction increases somewhat, and it is always
accompanied by the reaction :
2 NaOCl = O 2 + 2 NaCl. (11)
The last reaction is catalyzed by some metallic oxides, espe-
cially by the oxide of cobalt, to such an extent that all of the
hypochlorite can be decomposed in this way without forming
any chlorate. 6
Perchlorate cannot be formed by the further action of
chlorine on chlorate, but is produced by the decomposition of
chlorate, as will be explained below.
The Electrolysis of Alkali Chloride on Smooth Platinum Elec-
trodes without a Diaphragm
If a concentrated neutral solution of alkali chloride is electro-
lyzed between smooth platinum electrodes, the alkali is de-
posited on the cathode and reacts with the water according to
the equation :
2 Na + 2 H 2 O = 2 NaOH + H 2 . (12)
The hydrogen produced escapes, unless it is used up in reduc-
ing some substance in the solution. On the anode, chlorine is
liberated from the ionic form to free chlorine, as follows :
2C1- + 2F=C1 2 . (13)
The liberated chlorine partly dissolves in the water and at
first partially escapes from the solution. Soon, however, the
alkali hydrate produced at the cathode and the dissolved
ELECTROLYSIS OF ALKALI CHLORIDES 85
chlorine are brought together by the stirring produced by the
escaping hydrogen, and after this no more chlorine escapes
from the solution. Chlorine and alkali hydrate are produced
in equivalent quantities, so that the equation (5),
C1 2 + 2 NaOH = NaCl + NaOCl 4- H 2 O,
is practically quantitative. It is evident that only 50 per cent
of the chlorine liberated is obtained in the active form as hypo-
chlorite. As the electrolysis proceeds, the hypochlorite becomes
more and more concentrated, until finally a limiting concentra-
tion is reached, whose value is determined by a number of factors,
such as the material of the anode, the current densities on the
anode and cathode, the temperature, and the original concentra-
tion of the chloride solution. This is due to the fact that the
hypochlorite, almost from the start, is also decomposed by the
current, and this decomposition increases as the concentration
of the hypochlorite increases, until the amount decomposed is
just equal to the amount produced. This decomposition takes
place in two ways ; at the cathode the hypochlorite is reduced
by the hydrogen as follows :
NaOCl + H 2 = H 2 4- NaCl, (15)
and at the anode the hypochlorite ion is liberated, since it is
more easily discharged than the chlorine ion, 1 and reacts with
the water, producing chlorate and oxygen according to the
following reaction : 2
6 CIO- + 3 H 2 = 2 C10 3 - + 4 Cl- + 6 H+ + lO a . (1Q)
This has been called the anode chlorate formation, since it takes
place only on the anode and not throughout the solution.
It may help in understanding the chloride electrolysis if,
before discussing it further, a method of analysis is explained
which has been extensively used in the study of this subject
for following the reactions taking place during the electrolysis.
1 Foerster and Miiller, Z. f. Elektroch. 8, 634, (1902).
2 Foerster and Miiller, Z. f. Elektroch. 8, 667, (1902). This equation is con-
sidered fairly well established, as will be shown below, though other explanations
of the results are possible.
86 APPLIED ELECTROCHEMISTRY
This consists in analyzing the gas evolved from the cell and
comparing the amount of hydrogen and oxygen in it with that
evolved by the same current from a water coulometer. 3 If there
is less hydrogen from the chloride cell than from the coulometer,
the difference must have been used in reducing the hypochlorite,
according to equation (15), as this is the only reducible substance
in solution. The oxygen in the gas evolved from the cell con-
taining the chloride solution must be due to the discharge of the
hypochlorite ion, which reacts with the water according to equa-
tion (16), producing chlorate and oxygen. Oettel believed
that the reaction was simply the evolution of oxygen according
to the equation :
2 CIO- + H 2 = 2 HOC1 + i 2 , (IT)
and he therefore called this portion of the current loss " water
decomposition," but this view has since been found to be incor-
rect. Since the proportion of oxygen evolved to the hypo-
chlorite ions discharged is the same in either case, Oettel's
calculations will not be changed, but the explanation of the
oxygen evolution will be given by equation (16) in place of
(17). According to equation (17), the oxygen evolved is pro-
portional simply to a current loss without destroying hypochlo-
rite already formed, while according to (16) it is proportional to
a fraction of the current that changes hypochlorite to chlorate.
The following example, illustrating the use of gas analysis for
determining the yield in hypochlorite as the electrolysis pro-
gr,esses, is taken from Oettel. 3
The cell containing the chloride solution was connected in
series with a water coulometer. During a given time, at the
beginning of the electrolysis, 60 cubic centimeters of gas were
evolved from the coulometer and 32 cubic centimeters from the
chloride solution. In the coulometer, 40 cubic centimeters of
the gas must have been hydrogen. By analysis it was found
that the gas from the chloride solution had the following com-
position : 30 cubic centimeters of hydrogen, 1.6 of oxygen, and
0.4 of chlorine. This shows a difference in the amount of hy-
* I\ Oettel, Z. f. Elektroch. 1, 354, (1894).
ELECTROLYSIS OF ALKALI CHLORIDES 87
drogen in the two cells of 10 cubic centimeters. This amount
must therefore have been used to reduce the hypochlorite
already formed. Since 40 cubic centimeters of hydrogen repre-
sents the total current, or 100 per cent, the loss of current due
to reduction was 100 x |$ = 25 per cent. The loss due to the
evolution of chlorine equals 100 x - 1 , or 1 per cent. The 1.6
cubic centimeters of oxygen are equivalent to twice as much
hydrogen, or 3.2 cubic centimeters. The loss of current by
changing hvpochlorite to chlorate was therefore 100 x = 8
per cent. The current used to produce hypochlorite is propor-
tional to the amount of hydrogen evolved from the chloride
solution, diminished by the quantity of chlorine evolved, and
twice the amount of oxygen: 30 (3.2 -j- 0.4)= 26.4 cubic
centimeters. The current yield is therefore 100 x J| = 66 per
cent. This, of course, means that 66 per cent of the current
produces hypochlorite according to equation (5) :
Cl a + 2 NaOH = NaCl + NaOCl + H 2 O.
The rest of the current destroys hypochlorite already produced,
or produces chlorine which escapes from the cell. Chlorine is
evolved, however, only at the very beginning of the electrolysis,
before the hydrate and chlorine have had time to mix. The
following table sums up the results of this calculation :
Current used to produce hypochlorite 66 per cent
Current used to reduce hypochlorite 25 per cant
Current loss by changing hypochlorite to chlorate .... 8 per cent
Current loss due to evolution of chlorine 1 per cent
100 per cent
The curves in Figure 24 4 will illustrate the results of the elec-
trolysis of a neutral 4.37 normal sodium chloride solution with
a current density on the anode of 0.075 ampere per square centi-
meter and on the cathode of 0.18 ampere per square centimeter.
The electrolysis was continued for 18 hours, but the plots are
given for only 8 hours, as no change in the direction of the
* Miiller, Z. f. anorg. Ch. 22, 33, (1900), and Z. f. Elektroch. 6, 14, (1899).
FIG. 24. Electrolysis of a neutral, 4.37
normal sodium chloride solution
curves took place during the following 10 hours. The quanti-
ties of hypochlorite and chlorate were determined by direct
analysis, and are plotted in
terms of oxygen contained by
each in grams per liter. The
corresponding scale of ordi-
nates is on the left. The
other curves were obtained by
gas analysis as described
above. The scale of ordiiiates
for these is given on the right,
in per cent.
It will be seen that the
fraction of the current used in
evolving oxygen and for re-
duction, and the concentration
of the hypochlorite become
constant at the same time.
At first the concentration of the chlorate remains low, but
increases steadily as soon as the concentration of the hypo-
chlorite becomes constant. This shows that hypochlorite is
the first product of the electrolysis and that it is the starting
point for the formation of chlorate ; also that it is responsible
for the evolution of oxygen, as would be expected from equa-
The same general effect is produced by electrolysis at 50 C.,
except that the concentration of the hypochlorite becomes con-
stant at a lower value. This is due to the increase in the
hydrolysis of the chlorine as the temperature rises, thus pro-
ducing a greater concentration of hypochlorite ions on the
anode from the beginning. The quantity of hypochlorite ions
that has to be supplied to the anode from the solution before
they are discharged is therefore less than at a lower temper-
ature; consequently the concentration in the solution will not
reach as high a value as in the cold solution before the amount
of hypochlorite decomposed equals the amount produced. 6
6 Foerster, Elektrochemie wasseriger Losungen, p. 364, (1905).
ELECTROLYSIS OF ALKALI CHLORIDES 89
Both the reduction of the hypochlorite at the cathode and
the discharge of the hypochlorite ion on the anode are made
more difficult by increasing the current density, as will be seen
from the following considerations. The greater the quantity
of chlorine coming from the anode, the more it tends to prevent
the hypochlorite from reaching the anode, where it would be
discharged, 6 and the smaller the cathode is made, the less oppor-
tunity will the hypochlorite have of coming in contact with
nascent hydrogen. This is the explanation of the experimen-
tal fact that increasing the current density on the cathode low-
ers the reduction, and on the anode it makes the evolution of
oxygen less in the first stages of the electrolysis, which is equiv-
alent to making the concentration of hypochlorite attainable
In a dilute solution of chloride, the maximum hypochlorite
concentration is less than in a concentrated solution, because at
a given concentration of chloride the hypochlorite must carry
relatively more of the current than when there is a greater
amount of chloride present, and this results in its being changed
to chlorate. Table 10 illustrates the effects of temperature,
current density, and concentration changes on the electrolysis
of alkali chloride solutions.
The reduction of the hypochlorite can be nearly entirely pre-
vented by the addition of a small amount of potassium chro-
mate to the solution. 6 Under the action of the current a thin
diaphragm is produced that gives the cathode a brownish yel-
low appearance when compared with a fresh piece of platinum,
and which gives a test for chromium when dissolved in nitric
acid. 7 This diaphragm is probably an oxide of chromium,
since a cathode of metallic chromium does not prevent reduc-
tion. Potassium chromate is as effective with a low-current
density as with a high density. The curves 8 in Figure 25 show
the effect of adding 0.18 per cent of chromate to a solution con-
6 E. Miiller, Z. f. Elektroch. 5, 469, (1899); Imhoff, German Patent, 110,420,
7 E. Mtiller, Z. f. Elektroch. 7, 401, (1901).
8 E. Miiller, Z. f. Elektroch. 5, 470, (1899).
taining 30 per cent of sodium chloride. The broken lines refer
to the solution without the chromate. The current density
on the anode in both cases was 0.075 ampere per square centi-
meter ; on the cathode, 0.18 ampere. The temperature was
from 42 to 50 C.
H> s^ P -
4 8 12 16 20 24
FIG. 25. Electrolysis of sodium chloride
Full lines refer to solutions containing 0.18 per cent chromate, broken lines to solutions containing
When potassium chromate is added, the whole loss in current
will therefore be due to oxygen evolved according to equation
(16), which may be written :
6 CIO- + 3 H 2 O + 6 F = 6 H + + 2 C1O 8 - + 4 Cl~ + 1J O 2
But 12 equivalents of electricity are required to produce 6 equiv-
alents of hypochlorite, according to equation (5), which may be
12 Cl- + 12 F + 12 NaOH = 6 NaCl + 6 NaOCl + 6 H 2 O,
while 6 equivalents are required to discharge the hypochlorite ions
required by (16). If as much hypochlorite is to be decomposed
by (16) as is produced by (5), it is evident that twice as much of
the current must be used in producing hypochlorite as is used in
changing it to chlorate. That is, f of the current produces active
ELECTROLYSIS OF ALKALI CHLORIDES
oxygen in the solution and -J produces free oxygen, at the same
time changing the active oxygen from hypochlorite to chlorate,
according to (16). Therefore, excluding reduction and the for-
mation of chlorate by equation (7), when the concentration of
the hypochlorite has reached a maximum, in a neutral or slightly
alkaline solution, 33.3 per cent of the current will be used to
produce free oxygen, and 66.7 per cent to produce active oxygen
in the solution. 9 The oxygen evolution can never be greater
than 33.3 per cent unless the concentration of the solution is
small, in which case oxygen would be evolved by the discharge
of hydroxyl ions. Except for these points, this relation is inde-
pendent of the other conditions of the experiment, such as tem-
perature, current density, and, within certain limits, the
concentration. This is illustrated by the results in Table 10, 10
Solution : 4.8 Normal NaCl and 2 Grams K 2 CrO 4 per Liter
LIMITING CONC. OF OXYGEN
IN NaClO. GRM. PER
PER CENT OF CURRENT PRO-
SQ. CM. ON
30 to 33
30 to 31
The Solution Changed to One 1.7 Normal NaCl and Containing 2 Grams K 2 CrO 4 per
29 to 31
33 to 34
25 to 27
35 to 36
9 Foerster and Miiller, Z. f. Elektroch. 9, 199, (1903).
10 Foerster and Miiller, Z. f. Elektroch. 9, 196, (1903).
92 APPLIED ELECTROCHEMISTRY
In the above experiments, when the oxygen evolution is less
than 33.3 per cent, hypochlorite is lost by the secondary forma-
tion of chlorate. Columns 3 and 5 show that the maximum
concentration of hypochlorate is different under different con-
ditions, but that when this concentration is reached, the frac-
tion of the current used in oxygen evolution is practically the
same under widely differing conditions.
If the solution of sodium chloride is made acid with hydro-
chloric acid at the beginning of the electrolysis, the first effect
of electrolysis is to decompose the acid until the solution be-
comes nearly neutral. 10 There always remains a small quantity
of the free acid throughout the solution, however, liberating free
hypochlorous acid, which oxidizes the hypochlorate to chlorate
through the entire solution, according to equation (7). This
gives a method of increasing th&^ yield in chlorate over that
attainable in neutral or alkaline solutions, in which it has been
shown above that the maximum yield is 66.7 per cent. If,
before the maximum concentration of hypochlorite has been
reached, a quantity of acid is added to the solution which is
equivalent to only a fraction of the hypochlorite in the solution,
the latter is completely oxidized to chlorate. Further elec-
trolysis produces more hypochlorite, to which acid may again be
added, producing more chlorate. 11 By this means, chlorate can
be produced on smooth platinum electrodes with nearly 90 per
cent of the theoretical current yield. In place of adding the
requisite amount of hydrochloric acid from time to time, the
solution may be kept slightly acid by the addition of potassium
acid fluoride, KHF1 2 , as patented by the Siemens and Halske
Company, 12 or of alkali bicarbonate, which is patented by the
Aktiengesellschaft vorm. Schuckert & Co. 13
Oettel found in his early experiments that adding 0.3 gram
of potassium hydrate to 100 cubic centimeters of a solution
containing 20 grams of potassium chloride does not materially
affect the result of the electrotysis, but that as the alkalinity is
n Foerster and Miiller, Z. f. Elektroch. 8, 13, (1902).
12 Foerster and Miiller, Z. f. Elektroch. 10, 731, (1904).
1 3 Foerster and Miiller, Z. f. Elektroch. 8, 12, (1902).
ELECTROLYSIS OF ALKALI CHLORIDES
GRAMS OF N a O H PER LITER
FIG. 26. Effect of alkalinity on the elec-
trolysis of a solution of sodium chloride
increased, the maximum concentration of hypochlorite becomes
less, and the principal product of the electrolysis "is chlorate
and free oxygen. 14 The curves in Figure 26 15 show the quanti-
ties of chlorate and hypochlorife produced per liter by electro-
lyzing for one hour solutions
containing 200 grams of so-
dium chloride and varying
quantities of sodium hydrate
in one liter. The ordinates
are grams of oxygen per liter
contained in the chlorate or
hypochlorite of the solution,
and the abscissae, the number
of grains of sodium hydrate
added to one liter of the solu-
tion. The current density on
the anode was 0.04 ampere
per square centimeter.
This reduction in the hypo-
chlorite concentration and increase in that of the chlorate with
increasing alkalinity is explained as follows : The reaction by
which the chlorate is formed in strongly alkaline solutions is
the same as that in neutral or slightly alkaline solutions, and is
given in equation (16), and the difference produced by the
strong alkalinity is that the chloride finds hydroxyl ions with
which to react immediately on the anode, forming hypochlorite.
There is therefore a much higher concentration of hypochlorite
immediately on the anode than throughout the rest of the solu-
tion, and consequently its discharge and the production of
chlorate take place when the concentration throughout the
solution is very low. 16 When the alkalinity is further in-
creased, the hydroxyl ions also begin to be discharged and the
yield in chlorate falls below 66.7 per cent, which accounts for
the maximum point in the chlorate curve.
14 Z. f. Elektroch. 1, 474, (1895).
15 Miiller, Z. f. Elektroch. 6, 20, (1899) ; Z. f. anorg. Ch. 22, 72, (1900).
16 Foerster and Miiller, Z. f. Elektroch. 9, 182, and 200, (1903) ; also Foerster,
Elektrochemie wasseriger Losungeu, p. 366, (1905).
Another difference in the electrolysis of strongly alkaline
solutions is the effect of temperature. Higher temperature in
neutral solutions decreases the maximum concentration of hypo-
chlorite obtainable, but in
strongly alkaline solutions
the effect of temperature is
just the reverse, as shown in
the curves in Figure 27. 15
The ordi nates are the number
of grams of oxygen contained
in the hypochlorite or chlo-
rate in one liter of a solu-
tion originally containing 200
grams of sodium chloride and
40 grams of sodium hydrate
the same volume. The
FIG. 27. Effect of temperature on the
electrolysis of an alkaline solution of
electrolyses lasted one hour each, with a current density on the
anode of 0.045 ampere per square centimeter. Increasing the
anode current density tends to counteract this temperature
effect. From the explanation given of these curves 17 it does
not seem that the effect of temperature in strongly alkaline
solutions is thoroughly understood.
The Electrolysis of Alkali Chlorides with Platinized Platinum
Lorenz and Wehrlin 1 showed that the use of a platinized
platinum anode increases the maximum concentration of hypo-
chlorite, and that the oxygen evolution and the production of
chlorate do not begin at a time when, on smooth platinum,
under the same conditions of the experiment, the oxygen evolu-
tion would be considerable. When the electrolysis is continued
for a longer time, however, oxygen evolution and chlorate for-
mation begin just as on smooth platinum anodes, and according
to the same reaction. 2 The only difference is that a higher
17 Foerster and Muller, Z. f. Elektroch. 9, 205, (1903)
1 Z.f. Elektroch. 6, 437, (1900).
2 Foerster and Muller, Z. f. Elektroch. 8, 515, (1902).
ELECTROLYSIS OF ALKALI CHLORIDES
concentration of hypochlorite is produced before the quantity
decomposed in a given time is equal to that produced. This is
illustrated by the curves in Figure 28, obtained with a 5.1
normal solution of
10 1 J 4- I L^ c/,T~l 1 1 100
sodium chloride, con-
taining 2 grams of
per liter. 2 The brok-
en curves were ob-
tained with a smooth
platinum anode, the
solid curves with a
The ordinates on the
right give the per
cent of the current
yield and the per
cent of the current
used for the evolu-
tion of oxygen, while
on the left the ordi-
nates give the num-
ber of grams per liter of oxygen in the form of chlorate and
hypochlorite. The current density on the anode was 0.067
ampere per square centimeter. An explanation of the higher
concentration of hypochlorite obtained with platinized anodes
will be given below in discussing potentials and decomposition
FIG. 28. The electrolysis of a 5.1 n. sodium chloride
solution, containing 2 grams of potassium chro-
mate per liter
Dotted lines refer to smooth platinum anode, full lines to
platinized platinum anode
The Electrolysis of Alkali Chlorides on Carbon Anodes
All carbon electrodes are more or less porous ; that portion
of their entire volume which consists of pores, or the porosity,
varies from 11.2 to 27.8 per cent for different kinds of carbon.
For Acheson graphite the porosity is 22.9 per cent. 1 The
porosity is calculated from the true and the apparent densities.
1 Foerster, Elektrochemie wasseriger Losungen, p. 372, (1905).
96 APPLIED ELECTROCHEMISTRY
The apparent density b is the weight of one cubic centimeter of
the material, while the true density a is the weight divided by
the volume actually occupied by the material. The value of a
is determined by mixing bromoform and chloroform in such
proportions that small pieces of the carbon will neither sink nor
float when saturated with the mixture. 2 The density of the
mixture is then determined by any of the well-known methods,
and thus gives that of the carbon directly. The value of the
porosity is then 100 - per cent.
On dipping a carbon electrode into a solution, the pores become
filled with the solution, and the solution contained in the electrode
is electrolyzed as well as that on the surface ; but since the dis-
solved salt cannot be replaced in the pores as rapidly as in the
solution on the surface of the electrode, where stirring replaces
the salt decomposed, the solution contained in the pores becomes
more dilute than on the surface. Consequently the evolution
of oxygen and the production of chlorate will begin sooner,
and the maximum concentration of hypochlorite will be less
than on a platinum electrode, when the other conditions of the
experiment are the same. 3
The effect of changing the chloride concentration or the
anode current density on the yield of hypochlorite and on the
maximum concentration attainable with carbon anodes is in
the same direction as with platinum electrodes.
A part of the oxygen liberated oxidizes the carbon to carbon
dioxide, part of which, remaining in the solution, makes the
solution slightly acid, and therefore changes the hypochlorite to
chlorate by equation (16). The formation of carbonic acid
takes place in solutions at 20 only to a small extent and after
several hours, but at 60 it begins at once, and the total quantities
contained in the gases evolved and dissolved in the solution
amount to as much as 27 per cent of the amount that would be
produced if this were the only product on the anode of the
2 Zellner, Z. f. Elektroch. 5, 450, (1899).
8 L. Sproesser, Z. f. Elektroch. 7," 1083, (1901).
* Z. f. Elektroch. 7, 944 and 1014, (1901).
ELECTROLYSIS OF ALKALI CHLORIDES 97
Carbon anodes are also subject to mechanical destruction, due
to crumbling, and in some kinds of carbon this may exceed the
loss due to chemical action.
The solution in the pores of the carbon may eventually be-
come so dilute that hydroxyl ions are discharged, causing the
production of hydrochloric acid around the anode ; for hydrogen
ions are left behind by the discharge of hydroxyl ions and, com-
ing in contact with chlorine ions migrating from the anode,
form hydrochloric acid. This fact will be shown later to be
of some practical importance.
Acheson graphite has been found to last better in the elec-
trolysis of chlorides than any other kind of carbon. 1
The Maximum Concentrations of Hypo chlorite and the Maxi-
mum Current and Energy Yields of Hypochlorite and
From what has preceded, it will be evident that the best
conditions. for obtaining a high concentration in hypochlorite
are to have a neutral, concentrated chloride solution, a low tem-
perature, platinized anodes, and to prevent reduction by potas-
sium chromate. Column 4 in Table 11 shows the maximum
amount of hypochlorite obtainable under different conditions
of the experiment. 1 The values given in grams of oxygen may
be changed to grams of chlorine by multiplying the former by
5^4^ = 2:22. 2 The solution was 4.79 normal with respect to
sodium chloride and contained 2 grams of potassium chromate
per liter. In the last experiment the solution was only 1.73
normal. Both electrodes were platinized.
Since the decomposition value of a concentrated solution of
sodium chloride on either smooth or platinized platinum is 2.2
volts, the minimum amount of energy necessary to produce
1 Foerster and Muller, Z. f. Elektroch. 8, 10, (1902).
2 Foerster and Muller use the ratio 4.44, which is the ratio of the chemical
equivalence of the chlorine and oxygen contained in hypochlorite. The ratio of
the weights contained, however, is 2.22.
one gram of oxygen in the form of hypochlorite is 7.4 watt
hours. From the table it is evident that with the lowest
current density this value is very closely approached.
GKAMS PER LITER
PEK SQ. CM.
Of 0, in
PER GRAM 2 IN
If chlorate is produced entirely secondarily by acidifying the
solution from time to time, no energy is required for its forma-
tion beyond the 7.4 watt hours necessary for the production of
the hypochlorite. By working in this way and by using plati-
nized electrodes, an average current yield of 98 per cent was
obtained in a run in which 3.66 volts were applied to the cell. 3
This is 12.5 watt hours per gram of oxygen in the form of
chlorate. The current density was 0.117 ampere per square
centimeter. By reducing the current density the theoretical
value of 7.4 watt hours could of course be more nearly
The Production of Per chlorates
A perchlorate is a more stable compound than a chlorate, since,
as is well known, a chlorate on heating first breaks up into
perchlorate, chloride, and oxygen, according to the equations : *
2 KC1O 8 = 2 KC1 + 3 O 2 , (18)
4 KClOg = 3 KC1O 4 + KC1. (19)
Foerster and Mtiller, Z. f. Elektroch. 8, 16, (1902).
1 Roscoe and Schorlemmer, Treatise on Chemistry, 1, 235, (1905).
ELECTROLYSIS OF ALKALI CHLORIDES 99
A solution of chloric acid is also unstable when its concentra-
tion exceeds a certain value, and breaks up as follows : 2
2 HClOg = HC10 4 + HC10 2 . (20)
The chloric and chlorous acids then react according to the fol-
lowing reversible reaction :
HC10 3 + HC10 2 ^ H 2 + 2 C10 2 . (21)
These reactions are similar to those by which hypochlorous
acid breaks up,
3HC1O = HC1O 3 +2HC1,
HC1O + HC1 ^ Cl 2 + H 2 O.
Perchlorates are produced in a purely chemical way only by
the breaking up of a chlorate, and not by direct oxidation.
The electrolytic production of perchlorate and of perchloric
acid was discovered by Count Stadion 3 in 1816, but the way
in which this oxidation takes place was not understood until
recently. This is not a direct oxidation of chlorate to per-
chlorate, as would be expressed by the equation :
ClOg- + 2 OH- + 2 F = ClO^ + H 2 O,
but is due to the discharge of the chlorate ions and their sub-
sequent reaction with water, as follows : 4
2 C10 3 - + H 2 + 2 F = HC10 4 + HC1O 2 + O. (22)
The oxygen does not escape, but oxidizes the chlorous acid
back to chloric acid :
HC1O 2 + O = HC10 3 . (23)
The principal facts concerning the production of perchlorate
are : (1) If the concentration of the chlorate is over 8 per cent,
a change in its concentration has no appreciable effect on the
current yield ; (2) the yield increases with increasing current
density; (3) the yield falls with increasing temperature;
(4) platinizing the anode decreases the yield and (5) in
2 Oechsli, Z. f. Elektroch. 9, 807, (1903).
3 Gilbert's Ann. 52, 218, (1816).
4 Oechsli, I.e., p. 819.
100 APPLIED ELECTROCHEMISTRY
electrolyzing alkali chlorides, perchlorate is not produced until
nearly all of the chloride has been changed to chlorate.
In an acid or neutral chlorate solution, perchlorate can be
produced with a high current yield, as Table 12 shows, giving
the results of an experiment in which 66 per cent sodium
chlorate solution was electrolyzed with a smooth platinum
anode on which the current density was 0.083 ampere per
square centimeter. The temperature was 9 C.
TIME IN MINUTES FROM BEGINNING
CURRENT YIELD PER CBNT
Alkalinity prevents the formation of perchlorates ; the cur-
rent yield falls to 16 per cent for a solution 0.242 normal with
respect to sodium hydrate, with the same current density as in
the experiment above. This is probably due to the smaller
number of chlorate ions that are liberated as the alkalinity is
increased, furnishing hydroxyl ions that are more easily dis-
charged than the chlorate. An increase in the current den-
sity would be expected to counteract this effect of the alkali,
and experiment shows that it does. The lower yield with
platinized anodes is due to the lower current density produced
by the larger surface.
The reduction in the yield by an increase in the temperature
is supposed to be due to the greater concentration of hydroxyl
ions of water from the increase in the dissociation with the
ELECTROLYSIS OF ALKALI CHLORIDES 101
The Electrolysis of Alkali Chlorides with a Diaphragm
If the object in electrolyzing an alkali chloride is to produce
an alkali hydrate and chlorine, the anode and cathode must be
separated in order to prevent the hydrate and chlorine from
mixing. There are four ways in which the separation of the
hydrate and chlorine is effected. These are: (1) by the use of
a diaphragm ; (2) by inclosing the anode in an inverted, non-
conducting bell, with the cathode outside ; (3) by charging a
mercury cathode with sodium in an electrolytic cell and decom-
posing the sodium amalgam with water in another vessel ; and
(4) by a mercury diaphragm, which acts as an intermediate
(1) Since electrolytic conduction takes place through a dia-
phragm, it is evident that the separation in this case will not
be perfect, for the diaphragm prevents only mechanical mixing.
The hydroxyl ions will migrate through the diaphragm and
react with the chlorine in the same way as described above.
The hydroxyl ions also pass through the diaphragm by ordi-
nary diffusion. Electro-osmosis, on the other hand, drives the
liquid through the diaphragm from the anode to the cathode,
and therefore opposes the diffusion and migration of the
hydroxyl ions. 1
If diffusion and osmosis just balance each other, the yield in
hydrate can be calculated as follows. 1 Before sodium hydroxide
appears at the diaphragm, the sodium chloride transports all
of the electricity, but when the hydrate is mixed with the
chlorine, the hydrate will also take part in carrying the current
through the diaphragm. If the fraction of the current carried
by the hydrate is x, that carried by the chloride will be 1 - x,
and x and 1 x must be proportional to the conductivities of
the hydrate and of the chloride in the solution. If L is the
conductivity of the chloride and L 2 that of the hydrate, this is
expressed by the equation :
1 Foerster and Jorre, Z. f. anorg. Ch. 23, 158, (1899).
102 APPLIED ELECTROCHEMISTRY
in which c and c 2 are the concentrations in moles per liter, a x
and 2 are the dissociations, and A/oc and X"oc are the conduc-
tivities at infinite dilution, of the chloride and hydrate respec-
tively. For potassium chloride and potassium hydrate, ^ =
0.545, and for sodium chloride and sodium hydrate, the value
of this fraction is 0.502. For potassium chloride and potas-
sium hydrate, equation (24) becomes
1= = 0.545^,
and for sodium hydrate and sodium chloride,
x" = - - - . (26)
1 + 0.502^
Now if all of the current were carried by the hydrate, and if
n were its transference number, n equivalents of hydrate would
pass out of the cathode compartment through the diaphragm in
the same time that one equivalent is produced. In this case
the yield in hydrate would be
A = 100 (1 - n) per cent.
The hydrate carries only a fraction of the current, however,
equal to x. The yield is therefore
A = 100 (1 nx) per cent.
The transference number, w, for potassium hydrate is 0.74, and
for sodium hydrate it is 0.83. 2 Substituting the values for x
in equations (25) and (26), and the values for n just given, for
ioo - ' 74
1 + 0.545 ^3
3 Foerster, Elektrochemie wasseriger Losungen, p. 400, (1905).
ELECTROLYSIS OF ALKALI CHLORIDES 103
and for sodium,
__mn - 83 _l
It is evident from these equations that, as the hydrate becomes
more concentrated, the fraction in the parenthesis becomes
greater, which reduces the value of A. Table 13 shows how
the yield decreases as the concentration increases. 3 The elec-
trolysis was carried out with 700 cubic centimeters of a solution
containing 200 grams of potassium chloride per liter in the
cathode compartment, and 500 cubic centimeters of the same
solution in the anode compartment. The electrodes were plati-
num, and the diaphragm was of Pukal clay. The current
density on the diaphragm was 0.016 ampere per square centi-
meter. The yield which was being obtained at the end of each
period was calculated by formula (27) from the values of the
concentrations of chloride and hydrate existing at the end of
the period, assuming that the dissociation of the hydrate and
chloride are equal.
YIELD FOR THE
LITER IN THE
1st 2 hrs.
2d 2 hrs.
3d 2 hrs.
4th 2 hrs.
It will be seen from the numerical values in equations (27)
and (28) that the yield of hydrate with potassium chloride will
be better than with sodium chloride, at 18 , to which temperature
these numbers apply. Since, however, all transference numbers
approach the limit 0.5 as the temperature is raised, these formulae
indicate that the yield in hydrate would increase with the tem-
Foerster and Jorre, Z. f. anorg. Ch. 23, 193, (1899).
perature and approach the same value for sodium and potassium
chlorides. Since a rise in the temperature also increases the
diffusion, the increase in the yield which would be predicted by
the formula would be somewhat too large. 3
Since the hydroxyl ions that migrate to the anode compart-
ment find an excess of chlorine, hypochlorous acid will be pro-
duced according to equation (2) :
C1 2 + OH- = HOC1 + C1-.
If this proceeded indefinitely, the loss in chlorine would be twice
the loss in hydrate. On platinum anodes this has been found to
be true in the first stages of the electrolysis. As the hypochlo-
rous acid becomes more concentrated, compared to the chlorine,
it will be neutralized by the hydroxyl ions coming through the
diaphragm, forming hypochlorite. This is then immediately
oxidized to chlorate by the excess of hypochlorous acid, accord-
ing to equation (7). Consequently, no hypochlorite is found
in the anode compartment.
The process in the anode compartment is essentially the same
when carbon anodes are
substituted for platinum,
with the exception, of
course, that carbon dioxide,
as well as oxygen, is pro-
(2) The principle of the
bell process is illustrated in
Figure 29. The anode is
placed in a bell and the
cathode outside. The cur-
rent flows under the lower
rim of the bell from anode
to cathode. Chlorine is evolved and passes out through the
tube in the top of the bell, while hydrate is formed on the
cathode. The process that takes place in this cell is very simi-
lar to that in a cell with a diaphragm. 4 At first the solution
Fio. 29. Bell process
4 Gustav Adolph, Z. f. Elektroch. 7, 581, (1901).
ELECTROLYSIS OF ALKALI CHLORIDES 105
in the anode compartment is divided into three sharply denned
layers, the upper one saturated with chlorine, next to this a
layer of unchanged chloride, and below this a layer containing a
large number of hydroxyl ions. The hydroxyl ions migrate
towards the anode, and on coming in contact with an excess of
chlorine react in the same way as when a diaphragm is used.
With carbon anodes in the bell process, a much higher
hydrate concentration can be obtained without destroying the
middle layer of the neutral solution separating the chlorine
from the hydroxide; at the same time, however, the current
yield is less than the theoretical. This is due to the fact that
free oxygen is always evolved on carbon anodes, producing free
hydrochloric acid. The hydrogen ions from this acid migrate
towards the cathode and neutralize the hydroxyl ions migrating
towards the anode, and thus prevent their coming in contact
with free chlorine. In consequence of this, much more highly
concentrated solutions of hydrate can be produced by the bell
process with the same energy yield than by the diaphragm
In actual practice the bell process is always carried out with
a circulating electrolyte. Fresh chloride solution flows into
the anode compartment, where it must be spread out uniformly
over the entire area of the bell, so that the neutral layer will
not be disturbed.
In the bell process the losses of chlorine and hydrate are
equal, so that the current yields in chlorine and hydrate
must also be equal. The chlorine dissolved in the anode solu-
tion is carried through the neutral layer by circulation and is
changed to hypochlorite on coming in contact with the hydroxyl
ions below. This is reduced on the cathode, producing an
equal loss in hydrate. The loss in chlorine at the anode by
the evolution of oxygen also produces an equal loss in hydrate,
for the hydrochloric acid left behind by the oxygen neutralizes
an equivalent amount of hydrate. 6
With a circulating electrolyte a current yield of from 85 to
5 Adolph, I.e. p. 589.
6 Otto Steiner, Z. f. Elektroch. 10, 320, (1904).
106 APPLIED ELECTROCHEMISTRY
94 per cent can be obtained, with the concentration of potassium
hydrate 120 to 130 grams per liter, and the chlorine 97 to 100
per cent pure, using a current density referred to the area of
the bell of 2 to 4 amperes per square decimeter, and from 3.7
to 4.2 volts. 7
(3) The third method of separating the hydrate from the
chlorine consists in depositing the metal in a mercury cathode,
which is then removed from the cell and treated with water.
The sodium or potassium reacts with the water, forming the
hydrate, and the mercury is returned to the cell to be used over
again. The losses in this process are due to the recombination
of chlorine dissolved in the solution with the alkali metal in the
amalgam, and to the reaction of the alkali metal with the water
before leaving the electrolyzing cell. The former loss may
amount to 100 per cent under some circumstances, while the
loss due to the decomposition of water is small. 8 In order to
reduce the recombination of the chloride and the alkali metal,
the current density on the cathode should be high and also the
concentration of the amalgam. Strange as it may seem, the
potassium amalgam is more resistant to chlorine, the more con-
centrated it is. For example, increasing the concentration of
the amalgam from 0.012 per cent to 0.06 per cent increased
the yield in comparable experiments from zero to 90 per cent.
A current density of 0.1 ampere per square centimeter gave an
88 per cent current yield. Since the principal loss is due to a
recombination of the chlorine and the alkali metal, the yield
will be the same for both alkali and chlorine. If the amalgam
is covered with a diaphragm to protect it from the chlorine,
current yields of 98 per cent can be obtained. 8
(4) The fourth method of separating the hydrate from the
chlorine consists in using mercury as an intermediate electrode.
The principle of this process is illustrated in Figure 30. The
electrolytic cell is seen to consist of three compartments ; the
two outer are the anode compartments containing the graphite
anodes AA, and the middle compartment contains the cathode
7 Z. f. Elektroch. 10, 330, (1904).
8 F. Glaser, Z. f. Elektroch. 8, 552, (1902).
ELECTROLYSIS OF ALKALI CHLORIDES
(7, consisting of an iron grid. The covers of the anode com-
partments have pipes, not shown in the figure, for leading off
the chlorine, but the cathode compartment is only loosely cov-
ered, so that the hydrogen escapes in the air.
The partitions separating the compartments do not quite
reach to the bottom of the cell,
but the opening is closed by a
layer of mercury covering the
bottom of the cell. The alkali
metal is electrolyzed into the
mercury in the anode compart-
ment and is electrolyzed out in
the cathode compartment. In
the Cathode compartment the FIG. 30. Cell with mercury diaphragm
amalgam is the anode, and the
alkali metal unites with the hydroxyl ions liberated on it and
forms hydrate. In order to stir up the amalgam so that the
alkali metal will get into the cathode compartment as soon as
possible, the whole cell is slowly tilted back and forth, causing
the mercury to flow from one compartment to the other.
In this system the current density on the cathode must also
be at least 0.1 ampere per square centimeter. 9 The speed of
rocking the cell also affects the yield, an increase in the rapidity
decreasing the yield. One of the difficulties encountered in
this process is that if the alkali metal becomes too dilute in the
amalgam, the mercury is itself oxidized in the anode compart-
ment. To avoid this, a part of the current is taken directly
from the mercury by a shunt circuit in which there is a suitable
resistance to make the shunted current about one tenth of the
total current. A decrease in the concentration of the chloride
solution reduces the current yield. With a 30 per cent potas-
sium chloride at a temperature of 40, and with a current
density of 0.1 ampere per square centimeter, Cantoni obtained
a current yield in hydrate of 90 per cent.
Le Blanc and Cantoni, Z. f. Elektroch. 11, 611, (1905). .
108 APPLIED ELECTROCHEMISTRY
Decomposition Points and Potentials of Alkali Chloride /Solutions
In a chloride solution before electrolysis there are only the
hydroxyl and chlorine anions, while after the electrolysis there
are also hypochlorite and chlorate anions. The cations are
the alkali metal and hydrogen both before and after electrol-
ysis. A knowledge of the potential differences between anode
and solution at which the different anions are discharged will
help in understanding the chloride electrolysis.
The potential difference at which an ionized substance is
discharged, or, what is the same thing, if the process is reversi-
ble, the potential difference produced by the substance when
brought in contact with a platinum electrode, is dependent on
its chemical nature and on its concentrations in the charged
and discharged conditions. Thus the potential difference
between a platinum electrode charged with chlorine and a
chloride solution is
T> rji Tf /T n rn\~ i~1
-flJ- i "'VcL MJLl i 7. i i VCL. (^9^
where' <7 clj is the concentration of free chlorine in moles per
liter surrounding the anode, tf cl _ is the concentration of chlo-
rine ions in the solution, and k is a constant. If <7 C1 and <7 C1 _
are both equal, the value of e is - log k, and is called the
electrolytic potential. For a solution saturated with chlorine
at atmospheric pressure containing 0.064 mole per liter, and
normal with respect to chlorine ions, e = 1.667 volts, 1 assum-
ing the potential of the dropping electrode to be zero. The
negative sign indicates that the solution is negatively charged.
Chlorine, cannot therefore be liberated at atmospheric pressure
at a potential difference less than this value. On a platinized
platinum cathode in an acid solution, normal with respect to
hydrogen ions, hydrogen would be liberated at 0.277 volt.
But the solution around the cathode is neutral to start with,
and soon after the electrolysis has begun is alkaline, due to the
i Miiller, Z. f. phys. Ch. 40, 158, (1902).
ELECTROLYSIS OF ALKALI CHLORIDES
formation of alkali hydrate. The hydrogen ion concentration
is then very much reduced below its value in the original
neutral solution. This alkalinity might have any value, but
for the purpose of calculation the solution around the cathode
will be assumed normal, though it would not reach such a high
value in a cell not containing a diaphragm. The value of the
potential of the cathode on tvhich hydrogen is being liberated
would then be 0.54 volt, 0.82 volt more positive than the po-
tential in a normal acid solution. 2 The cell would then have
an electromotive force of its own of
e = 0. 54 - ( - 1. 66) = 2.20 volts.
The decomposition point of a concentrated solution of sodium
chloride, determined, as usual, with a very small current, is
1.95 volts, but this is because the solution around the cathode
is more nearly neutral than assumed above. Continuous elec-
trolysis requires from 2.3 to 2.1 volts. 3
FIG. 31 . Curves showing the relation between current and anode potential, in
solutions of sodium chloride and of sodium hypochlorite
As was shown above, when the hypochlorite reaches a certain
concentration, the hypochlorite ion is also deposited on the anode.
It has never been possible to determine the decomposition point
of this ion, however. It is evident from the curves in Figure
31, 4 in which the decomposition points of two solutions are
2 Le Blanc, Electrochemistry, p. 209, (1907).
Lorenz, Z. f. Elektroch. 4, 247, (1897).
* Foerster and Muller, Z. f. Elektroch. 8, 634, (1902).
given, one normal with sodium hypochlorite and 0.025 normal
with sodium hydrate, the other normal with sodium chloride
and 0.01 normal with sodium hydrate, that hypochlorite ions are
not liberated before hydroxyl ions. This is shown by the fact
that there was no increase in the current below the potential
1.16 volts, approximately the point at which hydroxyl ions
are liberated in a normal hydrate solution. It is also evident
that the electrolysis of a normal chloride solution begins at a
higher potential than the hypocholorite solution. The decom-
position point of the hypochlorite ion therefore lies between
those of the hydroxyl and the chlorine ions.
Since there is a difference of about 0.5 volt between the de-
composition points of chlorine and hydroxyl ions, it would
seem impossible to liberate chlorine ions in a strongly
alkaline solution. This would be the case if it were not
that the potential of an anode on which oxygen is liberated
increases continuously, and eventually reaches the potential
at which chlorine is liberated. If it were not for this in-
crease in the potential, caused by the liberation of oxygen, the
decomposition of a chloride in an alkaline solution would be
impossible. 5 Another effect which tends to make chlorine de-
posit in an alkaline solution is the fact that the hydrate has a
depolarizing effect on the chlorine, in consequence of which
chlorine will be liberated at a lower potential than that neces-
sary for its deposition at atmospheric pressure. Table 14 shows
PER CENT YIELD IN ACTIVE OXYGEN
-1.21 to -1.27
- 1.30 to - 1.51
0.28 to 0.14
- 1.51 to - 1.595
0.5 to 0.4
6 Foerster and Mtiller, Z. f. Elektroch. 9, 184, (1903).
ELECTROLYSIS OF ALKALI CHLORIDES
that hypochlorite and chlorate are formed in a solution normal
with sodium hydrate, and 3.6 normal with sodium chloride, at
an anode potential below 1.667 volts, the potential at which
chlorine is liberated at atmospheric pressure. 6 The anode was
platinized platinum, of 14 square centimeters area.
It will be noticed that as the anode potential increases in nu-
merical value, the proportion of chlorate to hypochlorite in-
creases. This is due to the fact that the hypochlorite ions,
which are more easily discharged than the chlorine ions, are
more subject to deposition as the potential of the anode in-
1.3 ' 1.5 1.7 1.9 2.1
ABSOLUTE POTENTIAL DIFFERENCE BETWEEN ANODE AND SOLUTION
FIG. 32. Curves showing the relation between current and anode potential for
smooth and for platinized platinum anodes
creases, with the subsequent production of chlorate according
to equation (16).
On smooth platinum anodes the potential difference during
electrolysis is about 0.58 volt greater than on platinized plati-
num. 7 The decomposition points of sodium chloride on plati-
e Foerster and Miiller, Z. f . Elektroch. 9, 183, and 201, (1903).
7 Z. f. Elektroch. 6, 437, (1900).
112 APPLIED ELECTROCHEMISTRY
nized platinum and on smooth platinum anodes shows the same
difference, as is seen from the curves in Figure 32. 8 It is evi-
dent that the overpressure of an anion is a function not only of
its own chemical nature, but also of the solution from which it
is deposited, of the current density, and of the material com-
posing the anode.
The cause of this overpressure of 0.58 volt on platinum is not
well understood; it may be due to the resistance of a film of gas
liberated on the anode. There is a corresponding overvoltage
in other solutions, such as sodium hydrate and sulphuric acid,
where oxygen, in place of chlorine, is liberated. These over-
pressures are not equal for the same current density in these
different solutions. 9
Though the overpressure on smooth platinum anodes may
not itself be understood, its presence offers a possible explanation
of the higher concentration of hypochlorite obtained with a
platinized anode, for the relation between the decomposition
potential and the concentration of ions is that the decomposition
potential decreases as the concentration increases. Therefore,
with a lower anode potential, the concentration of the hypo-
chlorite ions would have to be greater before decomposition
takes place. 10
It is an experimental fact, as has been stated above, that very
little perchlorate is produced until most of the chloride has been
changed to chlorate. This is due to the fact that the decom-
position potential of normal sodium chlorate is 2.36 volts, 11 while
that of the chloride is 1.95 volts. 3 The high potential re-
quired for the deposition of the chlorate cannot therefore be
reached until most of the chloride has been used up.
When chlorine- is dissolved in water, according to equations
(2) and (4), a certain amount of hypochlorous acid and hypo-
chlorite will be produced. Both hypochlorous acid arid hypo-
chlorite are oxidizing agents, and therefore give an unattackable
s Miiller, Z. f. Elektroch. 8, 426, (1902).
Foerster and Miiller, Z. f. Elektroch. 8, 533, (1902).
i Foerster and Miiller, Z. f. Elektroch. 9, 199, (1903).
11 Wohlwill, Z. f. Elektrocb. 5, 52, (1898).
ELECTROLYSIS OF ALKALI CHLORIDES 113
electrode a definite potential. If the reactions by which they
give off oxygen, or what is the same thing, hydroxyl ions, are
HOC1 = OH- + Cl- + 2 F, (30)
CIO- + H 2 O = Cl- + 2 OH + 2 F, (31)
the potentials would be given by the equations
* V OH-
and for equilibrium concentrations,
tfj being taken from equation (29). When chlorine is liberated
on an unattackable anode, the equilibrium represented by (9),
= 3.6 x IP" 11 " ocl = 1.4 xlO' 17
must be established, and, assuming the chlorine electrode is re-
versible, the production of hypochlorite and hypochlorous acid
must be, according to (31) and (32), taken from right to left.
This means that a primary production of hypochlorite and
hypochlorous acid takes place on the anode to a small extent.
Fluorides, Bromides, and Iodides
The electrolysis of the other alkali halogen compounds has
not attained anything like the commercial importance of the
electrolysis of chlorides ; still, for the sake of completeness, the
behavior of the other alkali halides on electrolysis will be briefly
Fluorine decomposes water with the evolution of oxygen and
2 OH- + 2 Fl- = H 2 O + O. (35)
No oxygen compounds of fluorine are known, consequently the
electrolysis of fluorides offers nothing to compare with what
is obtained in the case of chlorides.
114 APPLIED ELECTROCHEMISTRY
Bromine enters into exactly similar equilibria when added
to alkali hydrate to those already described in the case of
chlorine. They are represented by the equations : l
Br 2 + OH- = HOBr + Bi-1
HOBr + OH- = BrO- + H 2 OJ '
Hypobromite is therefore always the first product of the reac-
tion when bromine acts on alkali hydrate. When one mole of
bromine acts on one equivalent of hydrate, the reaction is not
as complete as in the case of chlorine, but appreciable quantities
of bromine and hydrate remain unchanged.
The formation of bromate according to the equation
2 HOBr + NaBrO = NaBrO 3 + 2 HBr (37)
takes place with over 100 times the velocity of the correspond-
ing reaction for chlorate. This reaction takes place even in
slightly alkaline solutions with a high velocity, on account of
the greater hydrolysis of hypobromite, but in solutions that are
at least 0.1 normal with respect to hydrate, the hydrolysis has
been so far reduced that hypobromite is as stable as hypo-
chlorite. When a concentration of the hydrate is still further
increased, the rate at which bromate is produced increases,
probably according to the reaction :
3 NaBrO = NaBrO 3 + 2 NaBr. (38)
This differs from the corresponding reaction for chlorate, in
that it proceeds with scarcely any evolution of oxygen. This
reaction, however, is very much slower than that represented
by equation (37), and need not be considered in the practical
preparation of bromate.
In electrolyzing a bromide solution, free bromine is liberated
on the anode, accompanied by oxygen from the discharge of
hydroxyl ions, and produces hypobromite with the hydrate
formed at the cathode. The concentration of the hypobromite
increases up to a certain point, after which it remains constant,
and the only product of the electrolysis is then bromate. As
i Horst Kretzschmar, Z. f. Elektroch. 10, 789, (1904).
ELECTROLYSIS OF ALKALI CHLORIDES 115
the hypobromite increases in concentration, the evolution of
oxygen also increases, the hydroxyl ions for which are fur-
nished by the hydrolysis of the hypobromite.
Bromate is formed partly by the secondary oxidation of hypo-
bromite by hypobromous acid, which is always present to a
certain extent on the anode, and partly by direct oxidation
according to the equation :
The hypobromite ion is not discharged, so there is no reaction
between it and water, as there is in the case of the hypochlorite
The concentration of hypobromite attainable is greatest with
a high current density, a high concentration of bromide, and a
low temperature. It is also higher on platinized anodes than
on smooth, as is the case with hypochlorite. The highest con-
centration of hypobromite attainable is about the same as that
of hypochlorite, but the current yield is less, on account of the
greater tendency to form bromate. Unless potassium chro-
mate is added to the solution, bromate, as well as hypobromite,
is subject to reduction on a smooth platinum cathode, 2 which
is another point of difference between chlorate and bromate.
Perbromic acid and its salts cannot be produced by elec-
trolysis, and it is doubtful whether they exist at all. 3
When iodine is brought in contact with hydrate, the
I 2 +OH-=HOI + I- 1
HOI + OH- = 01- + H 2 I
are established exactly as in the case of chlorine and bromine. 4
Hypoiodite is very considerably hydrolyzed, and therefore,
unless the solution is very alkaline, it changes rapidly to iodate
by the reaction :
2 HOI + KIO = KIO 3 + 2 HI. (41)
2 H. Pauli, Z. f. Elektroch. 3, 474, (1897).
8 Roscoe and Schorlemmer, Treatise on Chemistry, 1, 358, (1905).
4 Foerster and K. Gyr, Z. f. Elektroch. 9, 1, (1903).
116 APPLIED ELECTROCHEMISTRY
If an excess of alkali is present, however, the hydrolysis is
driven back, and hypoiodite can be obtained free from iodate.
The formation of iodate is accelerated by an increase in the
temperature and concentration of the iodide, and by decreasing
The rapidity with which hypoiodite changes to iodate is
shown by the following facts : If 50 cubic centimeters of a
0.1 normal iodine solution are mixed with 50 cubic centimeters
of a normal sodium hydrate solution at zero degrees, a 0.05
normal hypoiodite solution would be 100 per cent yield. Imme-
diately after mixing, however, there is only 95 per cent of this
amount of hypoiodite, and after 2 minutes, only 75 per cent
remains. On dilution it is more stable ; a 0.01 normal hypoio-
dite solution remains practically unchanged for a few minutes
in a 0.1 normal alkaline solution at room temperature.
On electrolyzing a neutral solution of alkali iodide, 5 the io-
dine liberated on the anode comes in contact with the hydrate
from the cathode, and the first product is hypoiodite. This
changes over to iodate rapidly, as shown above, even in an alka-
line solution, so that the electrolysis of an alkali iodide solution
is similar to that of a slightly acid chloride solution. Conse-
quently the hypoiodite solution reaches a limiting concentra-
tion, after which the product of the electrolysis is exclusively
iodate. This limiting concentration of hypoiodite is determined
by the current density, temperature, and the concentration of
iodide and alkali. An increase in the alkalinity increases the
limiting concentration of the hypoiodite, while it decreases
that of the hypochlorite. This is due to the different ways
in which iodate and chlorate are formed in alkaline solutions.
As the hypoiodite never can become concentrated, the possi-
bility of the electrolytic discharge of the hypoiodite ion is
very small. Therefore the oxygen evolution, which takes place
only when the iodide is dilute and the solution is alkaline,
must be due nearly entirely to the discharge of hydroxyl ions.
It is therefore in no way connected with the formation of io-
6 Foerster and Gyr, Z. f. Elektroch. 9, 215, (1903).
ELECTROLYSIS OF ALKALI CHLORIDES
Periodates cannot be produced by the electrolysis of iodates
except with a diaphragm. 6 This is shown by the fact that
without a diaphragm no hydrogen is evolved on electrolysis,
but is all used in reducing the iodate. After electrolysis has
proceeded a while, the oxygen evolution also becomes zero.
There is then a constant amount of iodide and iodate in the
solution ; as fast as iodate is formed on the anode, it is reduced
on the cathode. In neutral solutions iodate is not oxidized to
periodate, and in alkaline solutions, potassium chromate does
not prevent the reduction of iodate to iodide.
By using a diaphragm, a current yield in periodate of about
26 per cent can be obtained. The best conditions are low tem-
perature, low-current density, and at least 4 per cent alkalinity.
2. TECHNICAL CELLS FOR HYPOCHLORITE, CHLORATE, HY-
DRATE, AND CHLORINE
Hypochlorite. Hermite's cell, patented in 1887, was the
first cell to be even moderately suc-
cessful for the electrolytic manufac-
ture of hypochlorite. 1 It consisted
of a rectangular box of ceramic with
a grooved channel around the top for
carrying off the solution of sodium
and magnesium chlorides, which
entered at the bottom. The cathode
consisted of numerous disks of zinc
supported on two slowly rotating
shafts running through the box and
separated from each other by a parti-
tion. The anodes, consisting of thin
sheets of platinum held on a noncon-
ducting frame, were placed between
the zinc disks. In practice this cell
FIG. 33. Elevation of Kellner
6 E. Muller, Z. f. Elektroch, 7, 509, (1901).
1 W. H. Walker, Electroch. Ind. 1, 440, (1903); Engelhardt, HypochJorite
and Elektrische Bleiche, p. 77, (1903).
g.ives a current yield of about 40 per cent and an energy yield
of one kilogram of chlorine for twelve kilowatt hours. 2
The Kellner cell, made by the Siemens
and Halske Company, is shown in Figures
33, 34, and 35. A glazed stoneware vessel
is divided into a number of compartments
by glass plates fitted into grooves in the
sides of the cell. The plates are wound
with platinum -iridium wire, which acts
electrodes, form- [f] [i fj H H'H \] 1} fi H]
ing the anodes
on one side and
the cathode on
the other side of
of the glass plates.
enters through holes in the bottom of
the cell and the electrolyzed solution flows out spouts at the
FIG. 34. Electrodes
FIG. 35. Plan of Kellner coll
FIG. 36. Kellner cell
top into a vessel containing a cooling coil. From here it is
pumped up through the cell again. This circulation continues
2 Engelhardt, I.e. p. 86.
ELECTROLYSIS OF ALKALI CHLORIDES
until the desired strength of hypochlorite has been obtained.
This is illustrated in Figure 36.
The Schuckert cell is also made by the Siemens and Halske
Company. It is made of stoneware and is divided into eight
FIG. 37. Horizontal section of Haas aud Oettel cell
or ten compartments, each having two graphite cathodes and a
Pt-Ir foil anode. The solution enters at one end and travels
in a zigzag direction through the different compartments. Each
cell has a cooling coil, and no pumps are needed for circulation.
The units are built in pairs and are designed for 110 volts.
The Haas and Oettel cell is shown in horizontal and vertical
cross sections in Figures 37 and 38. 3 The electrolyzer b is im-
mersed in the solution in the storage vessel a. The electrolyzer
consists of a vessel divided into several compartments c by
divisions r, made of carbon or any suitable material, and form-
ing the intermediate electrodes. The liquid enters the elec-
trolyzer through the passage d, one of which leads into each
compartment. As soon as the current is turned on, gas is pro-
duced in each compartment, which rises and, carrying the liquid
with it, causes it to flow through the channels e, as shown by
the arrows. This automatic circulation is very efficient. A
cooling coil in the container prevents the temperature from
rising too high. The electrolysis is continued till the concen-
tration of the hypochlorite has reached the desired value.
FIG. 38. Vertical section of Haas and Oettel cell
This cell was never put on the market in this country in the
form shown, 4 but an improved cell is made by the National
Laundry Machinery Company of Dayton, Ohio, the details of
which are not now available.
Among a number of other factors, the cost of the production
8 U. S. Pat. 718,249, (1903).
4 Communication from the National Laundry Machinery Company.
ELECTROLYSIS OF ALKALI CHLORIDES
of hypochlorite depends on the cost of salt and of power, and
on the concentration of the hypochlorite produced ; for, as was
shown above, the current efficiency of the production of hypo-
chlorite approaches zero as the concentration increases. For
cotton bleaching the hypochlorite is diluted to three grams of
active chlorine per liter, and is discarded after using. 5 Less
salt will therefore be lost if as much as possible is changed to
hypochlorite, but the cost of power increases as the concentra-
tion increases. The concentration to which it will be most
economical to continue the electrolysis will therefore depend
on the relative cost of power and of salt, assuming all other
conditions of the experiment constant. There will then be a
concentration of hypochlorite for which the cost will be a mini^
mum, assuming a definite cost for the salt and the power.
This minimum cost is found by plotting as ordinates the cost
The Kellner Cell
CONC. KG. PER
C1 2 PER L.
KW. HR. PER
KG. SALT PER
6 W. H. Walker, Trans. Am. Electrochem. Soc. 9, 23, (1906).
of power for a definite amount of hypochlorite at different con-
centrations, and also as ordinates the cost of the salt required for
the different concentrations of hypochlorite. The curve repre-
senting the sum of these costs will be found to have a minimum
Table 15 gives some data on the yield of active chlorine in
the Kellner cell, taken from cells in actual operation. 6
The yields of active chlorine in the Haas and Oettel appara-
tus are given in Table 16 7
The Haas and Oettel Cell
Clj PER L.
PER CENT CURRENT YIELD
KW. HR. PER KG.
ACTIVE C1 2
KG. SALT PER KG.
ACTIVE C1 2
The yields in active chlorine for the Schuckert cell are given
in Table 17. 1
The Schuckert Cell
CONC. PER CENT
GRM. ACTIVE C1 2 PER L.
KW. HR. PER KG.
ACTIVE C1 2
KG. SALT PER KG.
ACTIVE C1 2
6 Englehardt, I.e. p. 158.
7 Oettel, Z. f. Elektroch. 7, 315, (1900).
ELECTROLYSIS OF ALKALI CHLORIDES 123
Chlorate Cells. Since chlorate is made directly from hypo-
chlorite, a chlorate cell would not be expected to differ from a
hypochlorite cell in any mechanical details. The earlier chlo-
rate cells, however, contained a diaphragm, and the cathode
solution was allowed to circulate to the anode compartment.
This was to prevent the reduction of the hypochlorite from
which the chlorate is produced ; but since the discovery of the
action of potassium chromate, reduction can be avoided with-
out a diaphragm.
The first process to be used in practice was that of Gall and
Montlaur, patented in 1884. 8 This cell originally contained a
diaphragm to prevent reduction, and the solution circulated
from the cathode to the anode by means of external pipes. The
solution must, of course, leave the anode compartment as rapidly
as it flows in, but whether it leaves the cell entirely or returns
to the cathode compartment is not stated. Since 1897 the
diaphragms have been given up. A plant employing this pro-
cess was put in operation at Vallorbe in 1891, and another in
St. Michel, Savoy, in 1896. Very little information concerning
these plants has been published.
In 1892 the National Electrolytic Company at Niagara Falls
employed the chlorate cell of W. T. Gibbs. 9 A number of
these cells clamped together are shown in Figure 39, and a side
elevation of one cell on the line 22 of the preceding figure, in
Figure 40. 10 Each cell consists of a frame A made of wood with
a metallic resistant lining B. The rods forming the cathode
are attached on one side of this frame, and on the other, the
anode, consisting of a metallic plate D faced with platinum E.
Copper is preferred for the cathode and lead for the plate D.
Successive frames are separated from each other by gaskets F.
G- are supply tubes and .ff are vents for the escape of gas and
liquid. The cells are clamped together by the plates JK and
the bolts L. Each pair of electrodes is separated by the corre-
sponding gasket. The horizontal insulating rods prevent
8 J. B. C. Kershaw, Die Elektrolytische Chloratindustrie, p. 19, (1905).
9 J. W. Richards, Electrochern. Ind. 1, 19, (1902).
10 TJ. S. Pat. 665,426, (1901).
short circuit between the anodes and cathodes, which are only
from 1 to 3 millimeters apart. The electrolyte circulates from
the cell to a cooling vessel where the chlorate is precipitated.
FIG. 39. Gibb's cells clamped together
More chloride is then added, and the solution is returned to the
electrolyzing cell. A convenient size for these cells is 65 by
4-3 centimeters and 7.5 centimeters thick.
ELECTROLYSIS OF ALKALI CHLORIDES
The cell of Lederlin and Corbin, used at Chedde, is of the
open type. 11 It contains a platinum anode and two cathodes of
copper, bronze, brass, or iron. The anode has an area of 10
square centimeters and the cathode, 32.
FIG. 40. Section of single Gibb's cell
The chlorate is generally purified by recrystallization, and
the recrystallizing apparatus is an important part of a chlorate
The yield at Vallorbe was at first 55.9 grams per kilowatt
hour, though this has since been considerably increased. 12
11 Kershaw, I.e. p. 38.
Kershaw, I.e. p.
The yield obtained at Chedde with the Lederlin and Corbin
cell in a slightly acid solution containing potassium bichromate
was 0.69 gram per ampere hour, or 90 per cent of the theoretical.
Perchlorates. The cells used for the production of chlorates
can be used equally well for perchlorates. Whether there is a
difference in practice cannot be stated, for no description of a
perchlorate cell has been published.
Alkali Hydrates and Chlorine. In cells in which hydrate
and chlorine are to be the final product, the anode must be sep-
arated from the cathode so that the chlorine and hydrate can-
not mix. In the first type of cell to be considered, this is
accomplished by means of a porous diaphragm. A very large
number of such cells have been patented, but only a few need
One of the simplest of the diaphragm cells is McDonald's,
used by the Clarion Paper Mill at Johnsonburg, Pennsylvania, 13
and the United States Reduction and Refining Company in
Colorado. At the latter plant, there are 75 cells, producing
1500 pounds of chlorine in 24 hours. 14 Two vertical sections of
FIG. 41. McDonald cell
the cell are shown in Figure 41. It consists of a cast-iron tank,
1 foot wide, 1 foot high, and 5 feet and 2 inches long, with
two longitudinal perforated partitions. The perforations are
% inch in diameter, and there are 4 or 5 to the square inch.
A diaphragm is placed next each partition in the middle com-
13 Electrochem. Ind. 1, 387, (1903).
14 J. B. procker, Electrochem. and Met. Ind. 5, 201, (1907).
ELECTROLYSIS OF ALKALI CHLORIDES 127
partment, containing the anode. The diaphragms consist of
asbestos paper fastened to asbestos cloth by sodium silicate, and
are held in position by cement placed over both end walls and
the bottom of the anode compartment. This compartment is
closed by a cast-iron cover 5 inches deep, 6 inches wide, and
nearly 5 feet long, into which the anodes are cemented. It is
lined with cement and painted inside with asbestos varnish.
The anode cohsists of blocks of graphitized carbon, 4 inches
square and 10 inches long, into each of which a copper rod is
fastened by lead for the electrical connection. The partition
walls form the cathode.
The partition walls are flanged, forming a seat to hold the
cover, which is surrounded by a layer of cement. The chlorine
is conducted from the anode compartment by a lead pipe to a
gas main which leads to absorbing towers containing lime-
water. Brine circulates through the anode compartment.
The diaphragms last about 8 months, 16 after which time the
pores become clogged.
The sodium hydrate solution leaving the cathode compart-
ment contains from 7 to 18 per cent sodium hydrate. When
the diaphragm is new, the level of the liquid in the anode arid
cathode compartments is nearly the same, but when it becomes
more or less stopped up, the depth of the liquid -in the cathode
compartment is only an inch or two.
The Hargreaves-Bird cell consists of a cast-iron box 10 feet
in length, 14 inches in width, and 5 feet in height. 16 It is
divided into three compartments by two diaphragms made on
heavy copper gauze, which forms the cathode. The space
between the diaphragms is the anode compartment, through
which brine circulates. There is no liquid in the anode com-
partment except what percolates through the diaphragm.
Steam and carbonic gas are blown through the two outer com-
partments and change the hyrate formed on the outside of the
diaphragm to sodium carbonate. This cell takes 2000 amperes
at from 4 to 4.5 volts. The anode is a row of gas carbons,
is L. Rostosky, Z. f. Elektroch. 11, 21, (1905).
is Electrochero. and Met. Ind. 3, 350, (1905).
which last 30 to 40 days. The diaphragms last about the same
length of time.
The Hargreaves-Bird cell is shown in Figure 42, which is a
partial longitudinal section and side elevation, and in Figure
43, which is a section perpendicular to the length. 17 The
outside frame I is of iron lined with cement and bricks w,
which are saturated with tar to prevent leakage.- The space
FIG. 42. Hargreaves-Bird cell, side elevation
/ is the anode compartment through which the chloride solution
circulates, entering through the pipe g and leaving through h.
The diaphragms are made of asbestos paper, the pores of which
have been filled with hydrated silicate of lime or magnesia. 18
In the cathode chamber a number of copper strips b are placed,
imbedded in cement e, extending from the cover plate c to the
cathode c?, and inclined downwards. These direct the
17 U. S. Pat. 655,343, (1900).
U. S. Pat. 596,157, (1897).
ELECTROLYSIS OF ALKALI CHLORIDES
densed vapor against the cathode to wash away the alkali as it
is formed. The lower edges of the strips have openings, in
order to allow the steam and gas to
pass freely over the cathode, a', a r are
the injectors for supplying carbonic
acid gas and steam to the cathode
chambers. Z 2 , Z 2 are pipes for draining
the cathode chambers. The chlorine
passes from the anode chambers to the
towers, where it is absorbed by milk
The West Virginia Pulp and Paper
New York, use
this cell for
tions. 19 This
of two rows of
14 cells each,
FIG. 43. Harsreaves-Bird cell,
all connected in series.
Perhaps the most efficient diaphragm
cell in use is the Townsend cell, repre-
sented in cross section in Figure 44,
and in perspective in Figure 45. 20 The
anode space is inclosed between a lid (7,
two vertical diaphragms D, and a non-
conducting body H. Graphite anodes
pass through the lid on the cell. The
perforated iron cathode plates S are in
close contact with the diaphragms. These plates are fastened
to two iron sides J, which form the cathode compartment. The
anode compartment is filled with brine T, and the cathode corn-
is Electrochem. and Met. Ind. 6, 227, (1908).
20 Electrochem. and Met. Ind. 5, 209, (1907).
FIG. 44. Townsend cell
partment with kerosene oil K. The brine percolates through
the diaphragm, and, when the current is turned on, it contains
on passing the dia-
phragm, comes in
contact with the
forms drops which
fall to the bottom
of the compart-
ment, are collected
in the pocket A,
and are drained off
through P. The
solution leaving P
contains 150 grams
of sodium hydrate
and 213 grams of
salt per liter. The
salt is separated
by evaporation and
is used over again.
The continual percolation prevents nearly all diffusion of hy-
drate back to the anode. The rate of percolation for a 2500-
ampere cell is from 15 to 30 liters an hour. 21
The Town send cell is 8 feet in length, 3 feet in depth, and
1 foot in width, and consists of a U-shaped concrete body
against which the two iron side plates are clamped. A rubber
gasket is placed between the concrete and the iron to make a
tight joint. Brine circulates through the anode compartment,
and during its passage the specific gravity falls from 1.2 to
1.18. On leaving the cell it is resaturated and is then ready to
be passed through again. There is a loss in kerosene which
amounts in cost to about two dollars a day for a large plant.
The diaphragms of the Townsend cell consist of a woven
21 Baekeland, Electrochem. and Met. Ind. 7, 314, (1909).
FIG. 45. Townsend cell
ELECTROLYSIS OF ALKALI CHLORIDES
sheet of asbestos cloth, the pores of which are filled with a mix-
ture of iron oxide, asbestos fiber, and colloid iron hydroxide.
This mixture is applied with a brush like ordinary paint. Di-
aphragms may be renovated by scrubbing and washing the
surface with water, allowing to dry, and repainting with this
mixture. This operation is not. necessary more than once in
five weeks, and sometimes not for several months.
The current efficiency of the Townsend cell is as high as 96
or 97 per cent under ordinary conditions, with a current density
on the anode of 1 ampere per square inch and about 4 volts on
each cell. 22 This cell has been in use at Niagara Falls in the
plant of the Development and Funding Company since 1906.
This plant originally consumed 1000 kilowatts, and according
to latest accounts it was being increased to four times this
Not much information concerning the bell process as actually
arranged in practice is available. The process is carried out by
Aussig, and at
several places in
ure 46 shows
FIG. 46. Cell for Bell process
two cross sections of the cell, 25 of which are placed side by
side in each bath. 23 The solution leaving the bath is said to
contain 100 to 150 grams of alkali hydrate per liter, at a cur-
rent yield of 85 to 90 per cent and with 4 to 4.5 volts per cell. 24
The Castner cell 25 is represented in Figure 30. It is a slate
box 4 feet square, and 6 inches deep, the joints of which are
22 For laboratory tests on the efficiency of this cell, see Richardson and Patter-
son, Trans. Am. Electrochem. Soc. 7,311, (1910).
28 Z. f. Elektroch. 7, 925, (1901).
24 Haeussermann, Dinglers polyt. J. 315, 475, (1900).
25 U.S. Pat. 528,322, (1894).
made tight with rubber cement. 26 Two partitions, reaching to
within ^g inch of the bottom, divide the cell into three compart-
ments. The two outside compartments contain the graphite
anodes A, and the middle compartment, the iron cathode 0.
Brine circulates through the anode compartments, and pure
water is supplied to the cathode compartment. The cell is piv-
oted on two points at one end and the other is raised and lowered
FIG. 47. Whiting electrolytic cell, plan
about J inch once a minute, causing the mercury to circulate be-
tween the anode and cathode compartments. The hydrate
leaving the cathode compartment has a specific gravity of 1.27.
This is evaporated to solid hydrate in large iron pans. Each
cell takes about 100 pounds of mercury, which is a very large
item of expense. The current for each cell is 630 amperes at
4.3 volts, and the current efficiency is about 90 per cent.
ae J. W. Richards, Electrochem. Ind. 1, 12, (1902).
ELECTROLYSIS OF ALKALI CHLORIDES 133
The Whiting mercury cell is 27 of a different type from the
Castner cell. The sodium is not electrolyzed out of the amal-
gam, but the amalgam is withdrawn from the electrolyzing
chamber and treated with water in a decomposing chamber
where the hydrate is formed. A number of electrolytic com-
partments are placed in parallel and are operated successively.
FIG. 48. Whiting electrolytic cell, cross section
so that the cell is continuous in its action, though intermittent
This cell, shown in Figures 47, 48, and 49, is a massive con-
crete structure supported on four concrete pedestals, from
which it is insulated. It consists of a shallow box divided into
two compartments, A and B, by a concrete partition. The
bottom of the decomposing chamber is divided by low glass
partitions into a number of sections having V-shaped bottoms
^ Jasper Whiting, Trans. Am. Electrochem. Soc. 17, 327, (1910).
sloping at a slight angle towards the central slot D. These
slots lead through the concrete partition into the oxidizing
chamber B, where they turn upward and are closed by valves
E. The valves are operated by the cams F, which are attached
to a slowly revolving shaft Gr. The other ends of the slots are
connected by the channel H, called the distributing level.
This connects with a secondary channel /, which leads through
one of the side walls of the cell to a pump J", at the extreme
end of the oxidizing compartment. Mercury covers the bottom
of the decomposing compartment, filling the above-described
sections to a common level. The anodes K are slabs of
Acheson graphite, perforated to allow the chlorine to escape,
and rest upon the ledges L, placed at the ends of the section in
FIG. 40. Whiting electrolytic cell, longitudinal section
such a way as to make a very short distance between the anode
and the mercury cathode. The anodes are connected to the
dynamo by the leads M.
The oxidizing chamber is divided into three compartments
P, lined with graphite and sloping downward in successively
opposite directions, forming a zigzag path to the pump pit Q,
where the stoneware rotary pump J is placed. Brine fills the
ELECTROLYSIS OF ALKALI CHLORIDES 135
decomposing chamber, and water or alkali hydrate fills the oxi-
The action is as follows : The floor of several sections of the
decomposing chamber is covered with mercury, maintained at
a common level by the distributing level. The current flows
from the anode through the brine to the mercury and out by
the iron rods R, partly imbedded in the concrete. When the
electrolysis has proceeded about two minutes, the valve at the
point of exit of one of the sections is opened by the action of
the cam, and the entire mass of sodium amalgam in the section
sinks into the slot and through the connecting pipe into the
oxidizing chamber. When the mercury is out of the cell, the
valve is closed by the cam. Mercury free from sodium then
flows into the empty chamber by way of the distributing level,
until the common level is reached. In the meantime the
sodium amalgam in the oxidizing chamber flows by gravity
over the graphite plates P to the pump pit. On reaching this
point the mercury has been deprived of its sodium, and is
raised by the pump into the wall pipe of the decomposing
chamber, completing the cycle.
The brine is fed in between the electrodes from the recep-
tacles S, equal in number to the sections of the decomposing
chamber. They are formed in the cover of the decomposing
compartment, and are connected by a channel T. Glass tubes
lead from the bottom of the receptacle S through the anode
and terminate below the surface of the mercury near the middle
of each section. As long as the sections are filled with mer-
cury the lower ends of the tubes are sealed, but when the
mercury is drawn off, a definite quantity of concentrated brine
flows into the section.
The graphite slabs in the oxidizing chamber contain a large
number of channels through which the mercury flows. The
sides of the channels extend into the caustic solution and form
the cathode of a short-circuited couple. It is difficult to main-
tain good contact between the graphite and mercury on account
of the hydrogen evolved, but this difficulty was overcome by
boring holes j- inch deep and J inch in diameter at frequent
136 APPLIED ELECTROCHEMISTRY
intervals in the channels, and filling them with pure mercury
at the start. This mercury remains pure and makes good con-
tact with the amalgam and the graphite.
The cell used at the Oxford Paper Company's works in Rum-
ford, Maine, is 1.8 meter square. It consists of five sections
and takes a current of from 1200 to 1400 amperes at 4 volts.
This corresponds to an anode current density of 11 amperes
per square decimeter. The current efficiency is from 90 to 95
per cent. The temperature is about 40 degrees. Each cell
requires from 350 to 375 pounds of mercury. A 20 per cent
hydrate solution is obtained, though one with 49 per cent can
be made if desired. The chlorine gas is 98 per cent pure, the
remaining 2 per cent being hydrogen.
THE ELECTROLYSIS OF WATER
HYDROGEN and oxygen have a number of technical applica-
tions that require their manufacture on a large scale. Such
uses are welding with the
oxyhydrogen flame, as is done
in joining the lead plates of
storage batteries; hydrogen
is used for filling balloons,
and oxygen is used for chem-
ical and medicinal purposes.
Hydrogen and oxygen are
produced on a commercial
scale by the electrolysis of
aqueous solutions, and of
course the object of the large
number of patents taken out
in this field is to keep the
hydrogen and oxygen separate
from each other. For this
purpose the anode and cathode
compartments have to be sep-
arated by a partition of some
kind. The different methods
of separating the gases will be
FIGS. 50-53. Schmidt's apparatus for the
electrolysis of water
illustrated in the description
of the following cells.
The cell designed by Dr. O. Schmidt 1 is shown in sections
in Figures 50-53, and a general view in Figure 54. It consists
1 Engelhardt, Die Elektrolyse des Wassers, p. 24, (1902); Z. f. Elektroch. 7,
of a number of iron plates e having thick rims and separated
by diaphragms d. These plates are the cathode in one cell and
the anode of the following cell. Each plate has two holes in
the thick rims h,o and w, w' , so that the apparatus is traversed
above and below by two canals. The lower canals are for sup-
plying the water as it is decomposed, and the upper are for al-
FIG. 54. Schmidt's apparatus for the electrolysis of water
lowing the gases to escape. The canals w and h connect with
the cathode chambers, w' and o with the anode chambers. The
two canals for adding water, w and w', are connected with a
common filling tube W by the pipes w 2 , up, and at the other end
of the apparatus the two gas canals connect with reservoirs .ZTand
0, where the gas is separated from the liquid carried along with
it. The liquid then returns to its respective chamber in the
electrolyzer. The stopcock a is for emptying the apparatus.
The diaphragms are of asbestos with rubber edges to prevent
leakage. The electrolyte is a dilute solution of potassium car-
bonate. Each cell has 2.5 volts impressed, and the current
yield is nearly 100 per cent. The oxygen is on the average
THE ELECTROLYSIS OF WATER
97 per cent pure, while the hydrogen is 99 per cent. Either
gas may be purified by passing through red-hot porcelain tubes.
FIG. 55. Garuti and Pompili's electrolyzer
which combines the small impurity of hydrogen in the oxygen,
or of oxygen in the hydrogen, to water which is easily removed.
FIG. 56. Garuti and Pompili's electrolyzer
This apparatus is made at the Maschinenfabrik Oerlikon.
near Zurich, Switzerland.
An apparatus in which the separation of the hydrogen and
oxygen is effected by a different method is that of Garuti and
Pompili. 2 In this cell a partition of iron separates the anode
from the cathode, and this partition is prevented from becom-
ing an intermediate electrode
by keeping the voltage ap-
plied to the cell too low for
this to take place. The cur-
rent flows from the anode to
the cathode around the bot-
tom of the iron partition.
Figure 55 is a longitudinal
vertical section through the
center, Figure 56 is a horizon-
tal section of one end, Figure
57 is a vertical cross section
of the apparatus, and Figure
58 a plan view of conductor
A tank A of wood lined with
iron a contains the electro-
lyzer, which consists of an
inverted tank A 1 which is di-
vided into cells E by longitu-
dinal diaphragms. This cell
is made of iron and is open
4^ ^ only at the bottom. The
l^\ I \ anodes b and cathodes c are
placed one in each cell, taking
care that each anode is be-
FIG. 57. Garuti and Poinpili's electro-
tween two cathodes. The gas passes through an opening at
the top of each chamber into the reservoir containing the same
gas. The electrodes are insulated from the diaphragms by
combs I made of wood, the teeth of which enter the cells and
fill the spaces between the electrodes and diaphragm. L is a
handle for lifting out the electrolyzer.
2 U. S. Patent 629,070, (1899).
THE ELECTROLYSIS OF WATER
A 25 per cent solution of potassium hydrate is used. The
voltage per cell is not allowed to exceed 3 volts, so there is no
danger of the diaphragm acting as an
electrode. The diaphragms may be per-
forated near the bottom with a large num-
ber of small holes, as there is very little
danger of the gases becoming mixed at
The hydrogen obtained from this ap-
paratus is 98.9 per cent pure, the oxygen
97. This apparatus is used in Rome,
Tivoli, Brussels, and Lucern.
The cell of the Siemens Brothers and
Company and Obach 3 employs a parti-
tion which consists of metal gauze below
the water line. The current is con-
ducted through the meshes, which are
small enough to prevent the mixture of the gases.
Other cells, such as that of Schoop, 4 have nonconducting
These examples complete the different principles on which
technical cells for the decomposition of water are built.
FIG. 58. Garuti and Pom-
3 Engelhardt, I.e. p. 67.
4 Engelhardt, I.e. p. 44.
A PRIMARY battery is a cell so arranged that the energy of
a chemical reaction is obtained as an electric current, and in
which the chemicals are not regenerated by passing the current
through the cell in the opposite direction. When the battery
is run down, fresh chemicals must be supplied. A secondary
battery, or accumulator, is a battery in which chemicals are
regenerated by passing through the cell, after discharge, a
reverse current from some other source.
Before the invention of dynamos, primary batteries were the
main source of electric energy; but since this method of gener-
ating electricity is too expensive for use where a large quan-
tity of energy is needed, they were employed only for very
light work and for experimental purposes. They are still used
extensively for electric bells, for exploding the gases in engines
by electric sparks, railroad signals, and similar purposes.
Primary batteries of special forms are also the standards of
electromotive force, but this is rather a purely scientific branch
of the subject than a technical application, and will therefore
The first primary battery was due to Volta, and consisted in
a negative pole of zinc and a positive pole of copper dipping
into a solution of salt or dilute acid. The electromotive force
of this battery rapidly falls off if an appreciable current is
taken from it, on account of the hydrogen liberated on the
positive pole. This develops a back electromotive force and
also increases the resistance of the cell itself. The battery is
then said to be polarized. In order to have a battery that is at
PRIMARY CELLS 143
all efficient, polarization must be avoided. In the Smee cell,
this was done by substituting platinized silver for the positive
pole in place of the copper in the Volta cell. The rough sur-
face caused the bubbles of hydrogen to escape more rapidly.
In the Grove battery, devised in 1831, 1 the cathode consisted
of platinum dipping into nitric acid contained in a porous cup.
Outside the cup was dilute sulphuric acid and a zinc negative
pole. In this case the nitric acid acts as a depolarizer, oxidiz-
ing the hydrogen to water and itself being reduced to nitrous
gases. The electromotive force of this battery is between 1.6
and 1.7 volts.
The Bunsen cell is a Grove cell with carbon in place of plat-
inum for the positive pole.
In the chromic acid battery, due to Poggendorff, the electrolyte
is a solution of sulphuric acid and potassium bichromate. The
positive pole is carbon and the negative zinc, which is withdrawn
from the battery when not in use. The chromic acid acts as
depolarizer. The electromotive force is about 1.3 volts.
These batteries have at present little more than historical inter-
est. The use of primary cells is now nearly entirely confined
to the Leclanche, the Lalande, and the Daniell cells. Leclanche
brought out his cell in 1868. 2 It consists of a zinc rod forming
the negative pole and dipping into a solution of ammonium chlo-
ride. The positive pole is carbon in contact with manganese
dioxide for a depolarizer. When the circuit is closed, zinc goes
in solution as zinc chloride and the ammonium radical is deposited
on the carbon, which breaks up into ammonia and hydrogen.
The ammonia dissolves and the hydrogen is oxidized by the
manganese dioxide to water. This depolarization is not rapid,
however, consequently not much current can be taken from a
Leclanche cell at a time without the voltage dropping consider-
ably, but it recovers on standing. The electromotive force of
this cell on open circuit differs from one cell to another, varying
from 1.05 to 1.8 volts.
This cell is put on the market under a large number of different
1 Wiedemann, Die Lehre von der Elektricitat, 1, 867, (1893).
2 Wiedemann, I.e. p. 850.
FIG. 59. Carbon
of Sampson cell
forms and under different names. One of the best Leclanche
cells on the market is the Sampson cell. 3 The carbon of this cell
is shown upside down in Figure 59. It consists
of a fluted hollow cylinder of French carbon pro-
vided with a removable seal at the lower end and
filled with a mixture of carbon and manganese
dioxide. The cell set up is shown in Figure 60.
The Lalande cell, brought out in 1883, 4 con-
sists of zinc for the negative pole, a 30 per cent
solution of potassium hydrate for the electro-
lyte, and a plate or box of iron or copper in
contact with black copper oxide as depolarizer.
The hydrate is protected from the carbonic acid
of the air by a layer of oil. The zinc goes in
solution as sodium zincate, and the hydrogen
deposited on the positive plate is oxidized by
the copper oxide. The positive plate may also be an agglom-
erate porous plate of copper oxide. The electromotive force
of this cell is about 0.9 volt and is very constant. The oxide
when reduced to copper is easily
oxidized again by heating in the
air. The original method of La-
lande of making the porous copper
oxide plates was to press a moist
mixture of oxide, 4 or 5 per cent
clay, and 6 to 8 per cent tar, and
then to heat to redness. The
plates so produced were porous
and lasted well. This plate must
be reduced to copper over its en-
tire surface before its normal rate
is reached, on account of the poor
conductivity of copper oxide. This is done before assembling
A modern type of the Lalande battery is made by the Edison
8 N. H. Sneider, Modern Primary Batteries, p. 10, (1905).
4 Wiedemann, I.e. p. 854.
FIG. 00. The Samson cell
PRIMARY CELLS 145
Manufacturing Company at Orange, New Jersey, and is called
the Edison-Lalande Battery. This battery, shown in Figure
61, consists of a copper oxide plate between two zinc plates
dipping in a 20 or 25 per cent solution of sodium hydroxide.
The containing jar is porcelain. The zinc plates have mercury
added to them during casting, so that they are amalgamated
throughout. The copper oxide ^-^
plates are made from copper scale
which is finely ground and then
roasted until thoroughly oxidized.
The oxidized powder is then
moistened with a solution of so-
dium hydroxide and pressed into
cakes a little larger than desired
in the finished product. These
cakes are then dried and baked at
a bright red temperature, which
partially Welds the particles to- FIG. 61. -Edison Lalande battery
gether. After cooling, the plates are reduced to copper at
the surface by zinc dust, to make them conduct. They are
then washed and are ready for use. 5 The hydroxide solution
is covered with a heavy mineral oil to prevent its creeping up
the zinc plates and corroding them. This battery has an initial
electromotive force of 0.95 volt, but on continuous discharge
at normal rate it drops to about 0.6 volt. The capacity varies
from 100 to 600 ampere hours, depending on the size of the
The Daniell cell, brought out in 1836, 6 belongs to a different
class of cells, in which there are two liquids separated by a
porous partition. The positive pole is copper dipping in a con-
centrated solution of copper sulphate, and the negative is zinc
dipping in sulphuric acid. Copper is deposited on the positive
in place of hydrogen, thus avoiding polarization, and zinc goes
in solution forming zinc sulphate. The electromotive force of
this cell is about 1.1 volt.
The gravity cell, Figure 62, is a form of the Daniell cell
5 Private communication from the company. 6 Wiedemann, I.e. p. 859.
FIG. 62. The gravity cell
patented by Varley in 1854, but which did not become generally
known until 1884. It is now the principal commercial form of
the Daniell cell. 7 The gravity cell derives its name from the
way in which the two solutions are prevented from mixing.
At the bottom of a glass jar is a horizontal copper electrode
covered with cop-
per sulphate crys-
tals and a saturated
solution of copper
sulphate. On this
solution is care-
fully poured a di-
lute sulphuric acid
solution, in which
a horizontal zinc electrode is immersed. When in use the
migration of the copper ions towards the cathode prevents their
reaching the zinc, while if the cell stands on open circuit the
copper sulphate would finally reach the zinc by diffusion and
cover it with a layer of copper. This cell should therefore al-
ways be kept on a closed circuit through a few ohms resistance.
Dry cells are a type of primary battery that have recently
come into very general use. It is estimated that 50 million
a year are manufactured in the United States, a large majority
of which are of a standard size, cylindrical in shape, 15 centi-
meters long and 6.25 centimeters in diameter. 8 They are
essentially Leclanche cells with a very small quantity of elec-
trolyte. Their greatest field of usefulness is probably tele-
phony and next the ignition through spark coils. 9
The container or outside insulation is usually pasteboard,
sometimes waterproofed by paraflfine or pitch. Just inside of
the container is the cylindrical zinc negative pole, usually 15
centimeters high, 6.25 in diameter, and 0.3 to 0.55 millimeters
thick. Lining the zinc on the inside is a layer of a special
grade of pulp board, moistened with a solution of zinc and
i Schneider, I.e. p. 54.
8 D. L. Ordway, Trans. Am. Electrochem. Soc. 17, 341, (1910).
Burgess and Hambuechen, Trans. Am. Electrochem. Soc. 16, 97, (1909).
PRIMARY CELLS 147
ammonium chlorides. The zinc chloride is added for reducing
the local action. Inside the pulp board containing the electro-
lyte are placed the depolarizer and the positive pole. The de-
polarizer is manganese dioxide, mixed with carbon, graphite, or
a mixture of both. Graphite is used to give the cell a lower
resistance. A carbon rod at the center and surrounded by this
mixture is the positive pole. An average composition of this
filling mixture is the following : 9
10 parts of manganese dioxide,
10 parts of carbon or graphite, or both,
2 parts of ammonium chloride,
1 part of zinc chloride.
Sufficient water is added to give a proper amount of electro-
lyte to the cell, depending on the original dryness of the ma-
terials, their fineness, the quality of the paper lining, and
similar factors. The usual specifications for the manganese
dioxide are that it shall contain 85 per cent of the dioxide and
less than 1 per cent of iron. The cell is sealed up on top
with a pitch composition to hold in the filling material and to
prevent the cell from drying. The carbon rod extends above
the seal and is provided with a binding screw.
The electromotive force of this cell is between 1.5 and 1.6
volts. On a short circuit through an ammeter, a cell will give
from 18 to 25 amperes. The energy output of a cell of the
dimensions given above, discharged to 0.2 volt continuously,
varies from about 20 watt hours when discharged through
2 ohms to 57 watt hours when discharged through 40 ohms. 8
The primary cells described above are comparatively unim-
portant compared with one which is not yet realized, but on
which a great deal of time and work has been spent. This is
the cell in which carbon and oxygen are the elements con-
sumed. The present method of producing work by the com-
bustion of coal to run steam engines is very inefficient, as only
about 15 per cent of this energy is obtained as work, the rest
being lost as heat. If it were possible to devise a cell in which
carbon and oxygen would unite with the production of an
148 APPLIED ELECTROCHEMISTRY
electric current and no other form of energy, at ordinary tem-
perature, a much greater amount of energy could be obtained.
In order to calculate 10 the free energy, or energy that is
obtainable as useful work, of the reaction in question,
C + 2 =C0 2 ,
consider a reaction chamber, as shown in Figure 63, containing
carbon, oxygen, carbon monoxide, and carbon dioxide in equi-
Cfe CO Ok
FIG. 63. Reaction chamber
librium at a given temperature. The chamber has two pis-
tons separated from it by semipermeable membranes. The
semipermeable membrane at the end of the cylinder containing
oxygen is permeable to oxygen only, and that at the end of the
cylinder containing carbon dioxide is permeable only to carbon
dioxide. The maximum work that this reaction can produce
is then obtained by the following reversible process : one mole
of oxygen is admitted to the oxygen cylinder at atmospheric
pressure and is allowed to expand reversibly to the equilibrium
pressure of oxygen p 0z in the reaction chamber. The work
The oxygen is then forced into the reaction chamber through
the semipermeable membrane. In order to preserve equi-
librium, one mole of carbon dioxide must be simultaneously
withdrawn at the equilibrium pressure p COz into the carbon di-
oxide cylinder. The work produced in these two steps is evi-
dently zero. The carbon dioxide must then be compressed to
atmospheric pressure, in which step the work produced is
10 Nernst, Theoretische Chemie, 6th ed. p. 698, (1909).
PRIMARY CELLS 149
The sum of W l and TF 2 is the maximum work obtainable :
Tf,+ Wt = RTlog?!. (1)
It would be impossible to measure the pressure of oxygen in
this mixture directly, but its value at 1000 C. can be obtained
as follows: It has been found experimentally that at 1000 C.
carbon dioxide dissociates to 0.06 per cent, according to the
2 CO 2 ^ O 2 + 2 CO.
At a total pressure of one atmosphere, the equilibrium pressures
for this system are then :
Carbon dioxide 0.9991 atmosphere
Carbon monoxide .... 0.0006 atmosphere
Oxygen ....... 0.0003 atmosphere
Substituting in the equation for the mass action law,
K(Pco.^ = Po s (pco)*, (2)
K (I) 2 = (0.0003)(0.0006) 2 . (3)
It has also been found that at 1000 C. and atmospheric pressure
an equilibrium mixture of carbon monoxide and dioxide in the
presence of carbon has the following pressures :
Carbon monoxide .... 0.993 atmosphere
Carbon dioxide 0.007 atmosphere
Since jfiTis known from equation (3), the pressure of oxygen in
this system can be computed by substituting in equation (2) :
JT(0.007) 2 = z (0.993) 2 .
From this, x = 5.4 x 10~ 15 atmosphere.
Substituting in equation (1),
Tr l+ TT 2 = 1273 7? log 54 x 00 ^_ 16
= 70600 calories at 1000 C.
This gives the free energy of the reaction at 1000 C., and it may
be found at room temperature as follows : The heat of the
reaction at room temperature is Q = 97650 calories, and it would
be approximately the same at the absolute zero, on account of
150 APPLIED ELECTROCHEMISTRY
the small change in the heat capacity of carbon and oxygen
before and after uniting. This would also be the free energy
at the absolute zero, since free energy and the total energy of a
.reaction are equal at this temperature. The free energy at the
absolute temperatures 1273 and being known, it may be
interpolated for 20 by the formula,
Fi + TT 2 = 97650 - 9765 "J 0600 x 293
= 91470 calories at 20 C.
The ratio of the free to the total energy is therefore approxi-
mately |i*-, corresponding to 94 per cent.
If the carbon of the carbon electrode enters the electrolyte as
an ion with four positive charges, and the oxygen as an ion with
two negative charges, the electromotive force of this cell would
be found from the equation,
4 .EF= 91000 calories ;
from which E = = 0.99 volt.
4 x 23100
The difficulties in realizing this cell consist in finding an elec-
trolyte in which carbon will dissolve, and in making an oxygen
electrode. So far they have been insuperable, and at present
there seems very little prospect of success.
Attention has been called by Ostwald n to an important point
in this cell, that the carbon and oxygen must form the opposite
poles of the cell and must act on each other through an inter-
vening electrolyte. If the carbon and oxygen acted directly on
each other, local action would result, and no current would be
A number of attempts have been made to make a carbon
oxygen cell, all of which employed some fused salt or hydrate as
electrolyte. This is a disadvantage to start with, for energy
will be lost by radiation in keeping the cells at a temperature of
several hundred degrees centigrade. One of the first of these
attempts was made by Jablochkoff 12 in 1877. In this cell the
11 Z. f. Elektroch. 1, 122, (1894).
12 E. de Fodor, Elektricitat direkt aus Kohle, p. 41, (1807).
PRIMARY CELLS 151
carbon was dipped into melted potassium nitrate, and the posi-
tive electrode was iron. This cell could never be successful,
for the carbon is brought directly in contact with the oxidizing
substance. Also, the oxygen was not taken directly from the
air, but was in the expensive form of a nitrate.
In 1896, W. W. Jacques patented a cell which excited a
good deal of interest at that time. This consisted of an iron
pot containing a melted mixture of potassium and sodium
hydrate, into which a carbon rod dipped ; air was blown against
the iron pot, which formed the positive pole, the idea being that
this oxygen would combine with the carbon through the inter-
vening electrolyte and produce a current. It is evident that
the hydrate would be changed to carbonate and that some
method would have to be used to regenerate it. The carbon
was in the expensive form of electrodes. There was a certain
amount of direct oxidation of the carbon, for the air also came
in direct contact with the hot carbon electrode. For these
and other reasons this cell has not been a success.
In conclusion, it may be said that the chance of finding any
solvent in which carbon would dissolve as ions is very remote,
and to find one in which both oxygen and carbon would thus
dissolve is still more remote ; consequently it seems hardly
possible that this problem will be solved by such a direct
THE LEAD STORAGE BATTERY
1. HISTORY AND CONSTRUCTION
THE lead storage battery in the charged state consists of
a positive plate of lead peroxide and a negative plate of finely
divided lead, both dipping in sulphuric acid of about 1.2 specific
gravity. When discharged, the surface of both plates has been
changed to lead sulphate. The plates may be brought back
to their original condition by sending a current through the
battery in the reverse direction.
This battery was invented in 1860 by Gaston Plante. 1 The
original battery consisted of two lead plates separated by
flannel and rolled together, and immersed in sulphuric acid.
The flannel was soon replaced by thin strips of rubber, on
account of its being eaten away by the acid. The battery
was charged from two Bunsen elements in opposite directions
six or eight times on the first day, allowing the cell to discharge
itself between each change in direction of charging. It was
noticed that the period of discharge continued to increase
regularly. The period during which the battery was sub-
mitted to the action of the current in the same direction was
then increased, and the battery was allowed to rest for eight
days, after which it was charged in the opposite direction.
The period of rest was then extended to two weeks, one month,
two months, and so on, and the duration of discharge continued
to increase. When sufficient capacity was reached, the plates
1 Gaston Plant^, The Storage of Electrical Energy, p. 30, (1887).
THE LEAD STORAGE BATTERY 153
were considered formed, and the charging current was then
always sent through the cell in the same direction. The reason
a thick layer of peroxide cannot be produced in one charge is
that it conducts the current and prevents the lead below it from
It is evident that this method of formation would be very
expensive. To overcome this difficulty, Metzger and Faure,
independently and approximately simultaneously, devised
methods of applying the active material to the plate in the form
of lead oxides. This method was patented by Faure 2 in 1880,
and has since been known by his name.^ Faure's original method
of applying the oxides was to coat the plate with a paste made
of the material and to hold it in place by means of some porous
material, such as felt or asbestos paper.
Charles F. Brush of Cleveland applied for a patent covering
this same field about a month before Faure, and the patent was
finally awarded to him. Eventually all of the essential patents
were acquired by the Electric Storage Battery Company of
The two general methods of making storage battery plates
now in use are only modifications of the original Plante or
The Plante process includes all methods in which the active
material is made from the plate itself, which must be of pure
soft lead. 4 Formation is accelerated in a number of ways.
Usually the first operation is to work up the surface mechanically
by cutting grooves, unless it is cast in this form. The next
operation is to produce the necessary amount of active material.
This is frequently done by allowing the plates to stand for a
certain time in some corroding solution of acids that produces
a thick layer of lead sulphate. This may then be reduced
electrolytically to lead or oxidized to lead peroxide. The acids
other than sulphuric must be thoroughly washed out before the
battery is ready for use. For example, a mixture of nitric and
2 U. S. Patents 252,002, (1882) and 309,939, (1884).
8 Watson, Storage Batteries, p. 10, (1908).
4 Watson, I.e. p. 21.
154 APPLIED ELECTROCHEMISTRY
sulphuric acids would have this effect of producing a layer of
sulphate. The other method of rapid Plante formation is
entirely electrolytic, according to the following principle :
The plate is electrolyzed as ail anode, but lead peroxide,
which would protect the plate from further action, is prevented
from forming by adding some salt or acid to the solution, the
anion of which separates at a lower potential than the peroxide
ion and causes the production of sulphate. Lead sulphate does
not conduct, so the current' has to penetrate to the lead below,
and as much sulphate may be produced in one step as is desired.
Such additions are acetates, tartrates, chlorides, nitrates, chlo-
rates, perchlorates, and the corresponding acids.
Peroxide is not always formed on a lead anode in sulphuric
acid, even when no substance is added to the solution to prevent
it, as is shown by the fact that the lead plate, which is the
anode, on discharging, becomes covered with sulphate. If
therefore a lead plate is short circuited in a solution of sul-
phuric acid with a peroxide plate, it will become covered with
sulphate, proportional in amount to the current that flows
through the plate. 5
In the Faure batteries the plates for holding the active ma-
terial consist of lead with about 5 per cent of antimony.
The active material is made by making a paste of lead oxide
and sulphuric acid and applying it to grooves cast in the sup-
porting grid. This paste sets and becomes hard, after which it
is changed to lead sponge and peroxide by electrolysis in a solu-
tion which may, or may not, be sulphuric acid.
The negative plates of the chloride battery, formerly made
by the Electric Storage Battery Company of Philadelphia, but
given up about eight years ago, 6 were made in an entirely dif-
ferent way. Lead and zinc chlorides were melted together and
poured into the supporting grid. The zinc chloride was then
dissolved in water, leaving the lead chloride in a porous condi-
tion. This was then reduced to sponge lead electrolytically.
The positive plates of this battery were made by the Plante
6 Dolezalek, The Theory of the Lead Accumulator, p. 194.
6 Private communication from the company.
THE LEAD STORAGE BATTERY
process. Though the method is no longer employed, the name
is retained. Figure 64 shows the positive and negative plates
FIG. 04. Positive and negative plates of the chloride accumulator
of one type of the so- called chloride accumulator. The positive
,plate contains buttons of lead strips wound up and held in a
grid. In the negative plate the active material is held in posi-
FIG. Go - The Gould battery plate
tion by perforated sheet lead, while the positive plate is of
the Plante type.
In the Gould battery, both plates are made by the Plante
method. A pure lead sheet is stamped out, and the surface is
worked up into the shape shown in cross section in Figure 65,
by rolling the surface a number of times with steel disks.
This process is called spinning. An unspun portion of the
plate is left where the wheels stop, forming a number of cross-
bars in each plate. A thin layer of lead peroxide is then pro-
duced by an electrolytic process. Negative plates are made by
FIG. (Hi. Positive Gould plate
reducing peroxide plates. 7 Figure 66 shows a positive plate
ready to be formed.
7 Catalogues O f the Gould Company.
THE LEAD STORAGE BATTERY 157
There are a large number of different types of batteries made
by different companies, information concerning which is best
obtained from their catalogues.
2. THEORY OF THE LEAD STORAGE BATTERY 1
The theory of the lead storage battery now generally ac-
cepted is known as the sulphate theory, and is due to Gladstone
and Tribe. According to this theory sulphuric acid combines
with the plates on discharge, and is set free on charge. On
discharge hydrogen is deposited on the lead peroxide and re-
duces it to lead oxide, which is changed to lead sulphate. This
is represented by the equation :
Pb0 2 + H 2 + H 2 S0 4 = PbS0 4 + 2 H 2 0. (1)
At the same time the sulphate radical is deposited on the lead
plate and changes it to lead sulphate :
Pb+SO 4 = PbS0 4 . (2)
The total change in the storage battery on discharge is the
sum of equation (1) and (2):
Pb0 2 + Pb + 2 H 2 S0 4 = 2 PbS0 4 + 2 H 2 0. (3)
In the discharged state both plates are covered with sulphate.
On charging, the reaction on the positive plate is :
PbSO 4 + S0 4 + 2 H 2 = Pb0 2 + 2 H 2 S0 4 ; (4)
and in the negative plate :
PbSO 4 + H 2 = Pb + H 2 SO 4 . (5)
The sum of equations (4) and (5) represents what takes
place in the whole battery on charging :
2 PbS0 4 + 2 H 2 = Pb0 2 + Pb + 2 H 2 SO 4 . (6)
Equation (6) is identical with equation (3) read from right to
left. The changes taking place both on discharge and charge
may therefore be represented by the following reversible equa-
Pb0 2 + Pb + 2 H 2 S0 4 : 2 PbS0 4 + 2 H 2 0. (7)
1 This discussion is taken mainly from Dolezalek's The Theory of the Lead
Accumulator, translated by Carl L. von Ende. John Wiley and Sons, (1904).
From right to left this represents the discharge, and from
right to left the charge.
In order to show that this equation represents what takes
place in the lead cell, it is necessary to show that the formation
or disappearance of each of the substances involved is propor-
tional to the amount of electricity that has passed. It must
also be shown that the substances involved are those given in
That the charged positive plate is the peroxide of lead and
not some other oxide or hydrate was shown by measuring the
electromotive force of different lead oxides and hydrates on
lead against a zinc electrode and comparing with a charged
positive plate. The results were the following :
Pb | Pb0 2
Pb 3 4
H 2 PbO,
- Zn = 0.42 volt
- Zn = 0.46 volt
- Zn = 0.75 volt
- Zn = 0.96 volt
Zn = 2.41 volts
A charged positive plate has a potential of 2.4 volts, showing
that lead peroxide is the compound that exists on the positive
Gladstone and Tribe showed, by analyzing the active mass
of the plates at different stages of charge and discharge, that
the production of sulphate on each plate is proportional to the
quantity of electricity
that has been taken
from the cell.
The same thing was
shown by W. Kohl-
rausch and C. Heim
by measuring the
specific gravity of the
acid on charge and
o 10 20 30 40 so eo discharge. The den-
AMPERE HOURS ., i ' - . -.
sity changed exactly
FIG. 67. Change in density of acid with charge and . J . J
discharge in proportion to the
THE LEAD STORAGE BATTERY 159
quantity of electricity that had passed through the cell, as
shown in Figure 67. A calculation of the change in specific
gravity by means of equation (7) agrees with that found.
This calculation is as follows :
The uncharged battery contained 3350 cubic centimeters of
acid of 1.115 specific gravity, corresponding to 16.32 per cent
acid. The total solution therefore weighed
3350 x 1.115 = 3735 grams,
0.1632 x 3735 = 610 grams of acid,
and therefore 3125 grams of water.
After charging with 50 ampere hours, according to equation
(7), the amount of water that disappeared was
50 x 2 x 0.336 = 33.6 grams,
and the amount of sulphuric acid formed was
33.6 x f| = 183 grams.
The solution therefore contained after charging
3125 - 33.6 = 3091.4 grams of water, and
610 -|- 183 = 793 grains of sulphuric acid.
The total weight was therefore 3884 grams, and the amount
of sulphuric acid contained was -ggfa X 100 = 20.42 per cent,
corresponding to a density of 1.146. The observed density
In order to see whether the heat of the reaction of equation
(7) and the electromotive force of the cell are in agreement,
the heat of the reaction may be substituted in the equation : 2
E= Q +T B , (8)
when E is the electromotive force and 2 Q is the heat of the
reaction of equation (7). Half of this value is used in equa-
tion (8), for 2 Q corresponds to the amount of material
changed by the passage of 2 coulombs of electricity. The
value of Q has been measured by Tscheltzow and by Streintz,
who found 43,800 calories and 42,800 calories respectively, for
2 Le Blanc, Electrochemistry, p. 173, (1907).
acid of a density 1.044, corresponding to 0.70 mole of acid per
liter. This concentration is taken, since at this value the tem-
perature coefficient of the electromotive force is zero. The
values of JE computed are
E= 1.86 volts (Streintz),
j=1.90 volts (Tscheltzow),
and the measured value for this density of acid gives 1.89 to
For acid of specific gravity 1.15, the values of Q are 42,600
calories and 43,600 calories respectively, and the value of is
+ 0.4 x 10- 3 volt. At 17 C., T= 290. Substituting in equa-
tion (8), .#=1.96 and 2.01 volts respectively. The measured
value is 1.99 to 2.01 volts. This calculation furnishes a con-
clusive proof that the reaction given in equation (7) is the one
that takes place in the lead accumulator.
It is evident that since the acid becomes more dilute on dis-
charging a lead battery, the electromotive force must decrease
with decreasing concentration. Table 18 shows the relation
between the concentration of the acid and the electromotive
force, from direct measurements.
DENSITY OF H,SO 4
PER CENT H 2 SO 4
ELECTROMOTIVE FORCE AT 15 C
It will be noticed that the electromotive force of the lead
storage battery, with the concentration of acid ordinarily used,
has the unusually high value for a battery of over two volts.
Sulphuric acid, if electrolyzed between platinum and electrodes,
gives a weak evolution of gas at 1.7 volts and at 1.9 a strong
evolution. If lead sulphate were spread in platinum, it would
therefore not be possible to reduce it to lead and oxidize it to
THE LEAD STORAGE BATTERY
peroxide, for the potential required could not be reached. On
lead, however, the overvoltage is so great that the gas evolu-
tion does not take place below 2.3 volts, which is greater than
y-mol. U^SO t
FIG. 68. Temperature coefficient of electromotive force of lead storage battery a&
function of the acid concentration
the voltage needed to change the sulphate in lead on one elec-
trode and peroxide on the other. If it were not for this high
overvoltage on lead, the lead storage battery would be an im-
The temperature coefficient of the lead storage battery for
the concentration of acid used is positive, but on decreasing the
concentration of acid the temperature coefficient falls to zero
and then becomes negative. This is shown by the curve in
Figure 68, representing the results of experiments in which the
temperature coefficient was determined between and 24 C.
The temperature coefficient is constant in value between 10
and 70 C. The heavy line in the plot gives the experimental
results, and the dotted curve the values calculated from equa-
The mechanism of the reactions taking place in the lead storage
battery has been explained with the help of the osmotic theory
by Le Blanc and by Liebenow. The difficulty in applying this
theory to the lead storage battery is to know what are the ions
in the case of the lead peroxide plate. According 'to Le
162 APPLIED ELECTROCHEMISTRY
Blanc's theory, the lead peroxide, having, a definite, though
slight solubility, dissolves in the dilute sulphuric acid and then
reacts with water according to the equation:
Pb0 2 + 2 H 2 = Pb + 4 OH-. (9)
During discharge the tetravalent lead ions give up two charges
of electricity and combine with the SO 4 ions to form lead
sulphate. The tetravalent lead ions are replaced, as they are
used up, by the solution of more lead peroxide. There is no
loss in free energy in this solution and reaction with water, for
both of these reactions take place at equilibrium concentrations.
The spongy lead electrode is similar to the zinc in a Daniell
cell. It goes in solution as a lead ion, but is precipitated on the
lead plate because of the low solubility of lead sulphate. The
hydrogen ions of the sulphuric acid combine with hydroxyl
ions of equation (9) to form water. The equations repre-
senting the reactions that take place subsequent to the reac-
tion of equation (9) for the entire battery are accordingly :
Pb + Pb + 2 S = 4 = 2 PbS0 4 , (10)
On charge the reverse of the above reactions takes place.
Both the positive and negative plates are covered with lead
sulphate, and the sulphuric acid surrounding the plates must
also be saturated with lead sulphate. On the negative plate
the lead ions are deposited as spongy lead, and on the positive
plate the bivalent lead ions are oxidized to tetravalent lead.
The solution and electrolysis are represented by the equations:
2 PbSO 4 solid = 2 Pb + 2 SO 4 , (12)
2Pb=Pb + Pb. (13)
The tetravalent ions then react with the hydroxyl ions accord-
ing to equation (9) taken in the reverse direction :
4 H 2 = 4 OH- 4- 4 H+, (14)
Pb + 4 OH- = Pb0 2 + 2 H 2 0. (15)
THE LEAD STORAGE BATTERY 163
The hydrogen ions corresponding to the hydroxyl ions and the
sulphate ions from equations (12) unite to form sulphuric acid :
4 H + + 2 S0 4 = 2 H 2 S0 4 . (16)
The sum of equations (9) to (11) and of equations (12) to
(16) will be found to result in equation (7). In support of
Le Blanc's theory it may be stated that tetravalent lead ions do
exist, and they are therefore probably capable of forming by
the electrolysis of lead sulphate solutions.
Liebenow's theory differs from Le Blanc's only as to the
action of the peroxide electrode. According to this theory the
lead peroxide goes into solution as doubly charged lead per-
oxide ions, so that the peroxide plate is to be considered a
reversible electrode with respect to the peroxide ions. On
discharge, the peroxide passes into the solution surrounding
the peroxide plate, which is already saturated with respect to
these ions. They then react with the hydrogen ions of the
acid as follows :
PbO 2 + 4 H+ = Pb + 2 H 2 O. (17)
The lead ions then combine with the sulphate ions to form
solid lead sulphate :
Pb + Sl) 4 = PbSO 4 solid. (18)
During charge, just the reverse reactions take place. The
lead peroxide ions are deposited on the positive plate, and are
replaced as they are used up by the solution of the sulphate
from the electrode and its hydrolysis :
Pb + 2 H 2 = Pb0 2 + 4 H+. (19)
In order to give Liebenow's theory some foundation it is neces-
sary to prove the existence of lead peroxide ions. This was done
by showing that on electrolyzing a solution of lead in sodium
hydroxide the concentration of the lead in anode compartment
increased. This shows that the sodium plumbite must be dis-
sociated according to the equation :
Na 2 PbO 2 = 2 Na+ + P~bO 2 . (20)
The electromotive force of the lead storage battery can be
164 APPLIED ELECTROCHEMISTRY
expressed by the Nernst formula by the aid of Liebenow's
theory. If P Pb o 2 is the electrolytic solution pressure of lead
peroxide and P Pb that of lead, and if the jt?'s refer to the osmotic
pressure of the ions, the potential difference between the per-
oxide plate and the solution is
and between the lead plate and the solution is
e2 = ^lo g ^. (22)
2 2 8 .. V J
The electromotive force of the cell is therefore
In confirmation of this theory, it has been found, as would
be predicted from equation (23), that in an alkaline solution,
in which the concentrations of the lead and lead peroxide
would be greater than in acid solutions, the value of E is less
than in acid solutions.
The work obtainable from a storage battery depends on its
capacity and the electromotive force measured at its poles
while the current is flowing. If V is the voltage on charging,
E is the open circuit electromotive force, I is the charging
current, and R is the resistance of the battery, then
F= E + IR, (24)
and on discharge
V = E - IR. (25)
If the current is kept constant and the value of Vis meas-
ured at short intervals, the charge and discharge curves ob-
tained are of the form shown in Figure 69. The value of V
rises rapidly in the first few minutes of the charge from 2.0 to
2.1 volts, and during the rest of the charge continues to rise
slowly, until at the end it suddenly rises to 2.5 to 2.7 volts.
During this period of rapid rise in the value of F", the cell
begins to evolve gas, after which the value of V changes only
slightly. On allowing the battery to stand on open circuit
THE LEAD STORAGE BATTERY
for several hours, the electromotive force E falls to the value
corresponding to the density of the acid. If the battery is
then allowed to discharge with the same constant value of the
current as used in charging, the value of V at first falls rapidly
"0 4 Hours
FIG. 69. Charge and discharge curves of the lead storage battery
to 1.9 volts and then gradually to 1.85 volts, after which it
decreases more rapidly to zero. The curves given in Figure 69
were obtained with about 20 per cent acid and a current density
of about 0.005 ampere per square centimeter of electrode sur-
face. With a greater current density the distance between the
charge and discharge curves would increase. The general
character of the curves for different makes of batteries is the
same, though for those having a thin layer of active material
the curves are more marked, and for those having a thick
layer, they are more rounded.
From the fact that the charging potential V is several tenths
of a volt higher than the discharging potential V, as is shown
in Figure 69, it is evident there is a loss of from 20 to 30 per
cent in the energy stored. It might seem at first sight that it
is due to the loss of energy due to the resistance of the cell
itself, to the IR value in equations (21) and (22), but the
value of the resistance of the cell is too small to account for
such a large loss. On open circuit the resistance of the
166 APPLIED ELECTROCHEMISTRY
smallest cells used is only several hundredtlis of an ohm, and
no large increase in its value takes place when a current is
passing. The cause of this loss in energy is the polarization of
the electrodes caused by the change in concentration of the acid
in the pores of the plates. On charging, acid is formed in the
pores of the plates where it becomes more concentrated than in
the rest of the battery on account of the fact that diffusion
does not take place with sufficient rapidity to equalize it.
Since the electromotive force of the battery increases with the
concentration of the acid surrounding the plates, a higher im-
pressed electromotive force will therefore be necessary in charg-
ing. On discharge, the acid is used up in the plates and
becomes more dilute than in the rest of the battery, and the
voltage falls correspondingly. The charge and discharge
curves of the lead battery may now be taken up in detail.
The Charging Curve. On closing the charging current, sul-
phuric acid is immediately set free at both electrodes and the
electromotive force therefore rises rapidly, as shown by the
portion of the curve AB. The rate of diffusion increases with
the difference in concentration of the acid on the plates and in
the rest of the battery, and when concentration difference has
become so great that the rate of diffusion and of formation are
equal, this rapid increase ceases. The maximum point at B is
probably due to the destruction of the thin continuous layer of
sulphate which forms on the electrodes during rest, thus reduc-
ing the resistance of the cell. The slow regular rise to O is due
to the gradual increase in the density of the acid and also to
the deeper penetration of the current lines into the active mass
and the corresponding greater difficulty in equalizing the acid
concentration by diffusion. The final rise CD takes place when
all of the lead sulphate on the surface of the plates has been
used up, and consequently the sulphate does not dissolve rapidly
enough to replace that electrolyzed out. Very soon the lead
and peroxide ions become so dilute that the work necessary to
deposit these ions is equal to that required to produce hydrogen
on the cathode and oxygen on the anode. If allowed to stand
on open circuit, sulphate diffuses from within the plate and brings
THE LEAD STORAGE BATTERY 167
back the electromotive force to the normal amount. The maxi-
mum point at D is due to the mixing of the concentrated acid
in the electrodes with that outside by the gas bubbles.
The Discharge Curve. In discharge the acid is used up in
immediate proximity to the electrodes, and this continues until
the concentration difference between the acid on immediate
proximity to the electrodes and in the rest of the battery has
become so great that diffusion just supplies the quantity used
up. During this time the value of V falls rapidly along AE*
The minimum point at ^is possibly caused by the formation of
a supersaturated lead sulphate solution. The solubility of lead
sulphate in a 20 per cent solution of sulphuric acid decreases
with decreasing concentration, so that at the beginning of the
discharge, when little solid sulphate is present, a supersaturation
of short duration is probable, and the electromotive force of the
battery decreases with increasing concentration of lead ions, as
seen from equation (23). The subsequent gradual fall in the
value of V represented by EF is due to the gradual decrease
in the density of the acid in the entire accumulator, but more
especially to the greater difficulty in the acid diffusing deeper
into the plate as the current penetrates deeper. Finally the
rate at which the acid diffuses cannot supply the acid used up
by the action of the current, and the value of V 1 falls off
According to this explanation, the loss in energy on charge
and discharge is due entirety to the concentration changes that
take place in the electrolyte within the active mass. The
smaller these concentration changes are, the more nearly will
the accumulator approach complete reversibility. This is il-
lustrated in Figure 70. These curves were obtained with
accumulator of 200 ampere hours capacity. It is seen that for
a current of 0.1 ampere, corresponding to a current density of
0.0017 ampere per square decimeter, the charging and dis-
charging potential differ by only 0.006 volt, or 0.3 per cent of
the electromotive force of the cell, and that by reducing the
current this loss may be still further reduced.
This loss is not distributed equally between the two plates.
The porosity of the lead plate made from the same sulphate
paste as the peroxide is about 1.4 times as great as the peroxide,
the potential of the peroxide plate falls off about 1.6 times
more than the lead plate for a given change in the concentni-
FIG. 70. Pole potential of the lead storage battery on charge and discharge as a
function of the current
tion of the acid, and finally the concentration change on the
peroxide plate is greater than on the lead, because not only is
sulphuric acid used up on discharge, but water is also formed.
All of these facts tend to make the loss on the peroxide plate
greater than that on the lead plate. When the positive and
negative plates are made of similar frames and paste, and have
approximately the same capacity, it has been found that 60 to
70 per cent of the loss takes place on the peroxide plate.
The capacity of an accumulator in actual practice means the
number of ampere hours that can be taken from it if discharged
to about nine tenths of its original electromotive force, the point
where the rapid falling off in the electromotive force takes place.
The capacity therefore is determined by the rate of discharge,
for the smaller the current the more time the acid has to pene-
trate by diffusion deeper into the plate, when all of the active
material on the surface has been used up. It is also evident
THE LEAD STORAGE BATTERY 169
that the conductivity of the acid will affect the capacity, for the
higher the conductivity the deeper will the current lines be able
to penetrate into the plate. Since there is a density of sul-
phuric acid at which there is a maximum conductivity, it would
be expected that the capacity of a lead storage battery would
have a maximum value for this density, and this has been shown
experimentally to be the case.
The current efficiency of a lead storage battery, or the ratio
of the number of ampere hours obtainable on discharge to the
number put into the battery on charge, is from 94 to 96 per
cent. The small loss of 4 to 6 per cent is due to self-discharge
and to the small amount of gasing that cannot be avoided.
The energy efficiency, on the other hand, which is the ratio of
the energy obtainable in the external circuit on discharge to the
energy put into the battery on charge, is only from 75 to 85 per
cent. The, cause of this comparatively low value, as explained
above, is the difference between the charge and discharge po-
tential. The loss in voltage due to the internal resistance is
only about 3 per cent with the usual acid concentration and
current density. The loss due to polarization is a minimum
when the conductivity of the acid in the battery is a maximum,
for in that case the lines of current spread over a larger surface
by penetrating deeper into the plate.
If a battery is allowed to stand on open circuit after charg-
ing, the electromotive force falls in fifteen or twenty minutes to
the value corresponding to the density of the acid. This is
due to solution around the plates becoming saturated with lead
sulphate. On discharge, when the voltage has fallen below the
value corresponding to the density of the acid, standing on open
circuit brings it back to the normal value. In this case the
recovery, as it is called, is due to the diffusion of the sulphuric
acid into the pores of the plate -where it has become exhausted.
If a charged cell is allowed to stand idle, the density of the
acid slowly decreases, and the amount of electricity obtainable
from it becomes less from day to day. This is known as self-
discharge, and for a cell in good condition amounts to from one
to two per cent a day ; if the acid contains impurities, however,
it may amount to 50 per cent a day. The self -discharge of the
lead sponge plate is more likely to take place than that of the
peroxide plate, as it is affected by a greater number of causes.
It is fatal for the lead plate if the acid contains any metal more
electronegative than lead in contact with sulphuric acid, such
as platinum or gold, for the impurity would be precipitated on
the plate and produce a short-circuited local element. The
lead would then tend to dissolve and deposit hydrogen on the
impurity. If the over-voltage of the impurity is not too great,
this would in fact take place, and the lead plate would be
changed to sulphate. Now the potential of the cell:
Pb sponge | Sulphuric acid | Platinized Pt -f- H 2
is 0.33 volt, hydrogen being the positive pole. A current could
be taken from this cell on closing the external circuit ; lead
sulphate would be formed on the lead pole and hydrogen would
be deposited on the positive pole. But if some metal were
substituted for platinum for which the over- voltage is 0.33 volt
or more, evidently hydrogen could not be liberated, and no
action would take place. Consequently only the metals stand-
ing on the left in the following table would be dangerous for
the accumulator ; those on the right could exist as impurities
in the acid without the least danger, even though some of them
are more electro-negative than lead.
Platinized Platinum .
Iron . . ...
As seen from this table, platinum is the most injurious impu-
rity. It has been found that one part of platinum in a million
of acid will produce a rapid self-discharge of the lead plate.
THE LEAD STORAGE BATTERY 171
It has been found, however, that metals when present together
can produce a rapid self -discharge, which alone cause scarcely
any action. An explanation of this cannot be given at present.
Contamination by platinum can easily occur when sulphuric
acid is used that has been concentrated in platinum retorts,
and plates once contaminated cannot be made available again.
All other metallic contaminations, if present only in traces,
become inactive on continued use of the cell, probably by
gradually alloying with the lead.
The self-discharge of the positive plate takes place more
slowly than that of the lead sponge plate. Metallic impurities
are of no effect on the lead peroxide, for they would not be
precipitated on it. The only kind of spontaneous discharge is
due to local action between the peroxide and the lead of the
support, which together form a short-circuited element, and
this is of importance only for plates with a thin layer of per-
Another cause of self-discharge of a battery is the presence
of salts of metals that can exist in more than one stage of oxi-
dation. For example, an iron salt would be oxidized to the
ferric state on the lead peroxide, and would then diffuse to the
lead plate and oxidize it to sulphate, thus gradually discharg-
ing both plates.
Sulphating. The plates of a strongly discharge battery on
standing gradually become covered with a white coat of lead
sulphate. If we attempt to recharge the battery, it is found
that the internal resistance has considerably increased, and it
does not begin to diminish until the charging current has
passed through the cell for some time; it then gradually ap-
proaches its normal value. A test of the capacity would show
that this has lost considerably in value. The phenomenon just
described is known as sulphating. This is not a very suitable
term, since in every discharge sulphate is formed on the plates,
which is changed back into peroxide and lead without any diffi-
culty. Elbs explains sulphating as follows : During discharge
there is formed on every particle of lead or peroxide a thin
layer of finely divided sulphate in contact with an acid solution
172 APPLIED ELECTROCHEMISTRY
saturated with the sulphate. If the accumulator is allowed to
stand in this condition, and is subject to any variation in tem-
perature, the large crystals will grow at the expense of the
smaller ones, for the sulphate increases in solubility as the tem-
perature rises, and the smaller crystals would be used up first,
both on account of their size and because the solubility of small
crystals is greater than that of large ones. When the tempera-
ture falls, the sulphate would be precipitated on the crystals
still remaining, and in this way the plate gradually becomes
covered with a continuous layer of lead sulphate crystals. Sul-
phating may be so bad that it is cheaper to replace the plates
than to regenerate them by charging.
THE EDISON STORAGE BATTERY
1. GENERAL DISCUSSION
THE Edison storage battery is the only accumulator besides
the lead battery that has any commercial importance. In this
battery the active material of the positive pole is an oxide or
oxides of nickel, and that of the negative pole, very finely
divided iron. The solution is 21 per cent potassium hydrate
with a small amount of lithium hydrate. 1
Edison began to investigate alkaline accumulators in 1898,
and after trying a great number of different combinations had
the nickel-iron combination fairly well developed in 1900. 2
It fhen passed through several more stages of development, and
arrived in 1904 at what was called the type E 18 battery. This
had twelve nickel plates arid six iron plates. The active mate-
rial of each plate was held in 24 perforated nickel-plated steel
pockets 7.5 centimeters in length, 1.27 centimeters in width,
and 8 millimeters in thickness. The iron plate was mixed
with mercury, the effect of which will be explained below, and
the nickel oxide with graphite, to increase its conductivity.
This battery had two defects : (1) the nickel plate continually
expanded on charging and did not contract on discharge, so
that the contacts between the active material and the supports
became bad, and (2) the graphite mixed with the nickel oxide
gradually disintegrated and did not fulfill its function of con-
ducting the current into the interior of the nickel plate, caus-
ing the battery to lose its capacity. 1
1 Walter E. Holland, El. World, 55, 1080, (1910).
2 Kennelly and Whiting, Trans. Am. Klectroch. Soc. 6, 135, (1904).
FIG. 71. Iron electrodes of tlie Edison storage battery
FIG. 72. Nickel electrodes of the Edison storage battery
THE EDISON STORAGE BATTERY 175
Both of these difficulties seem to have been overcome in the
latest form of this battery, the A type, which has been on the
market since 1908. The construction of the iron electrode,
shown in Figure 71, has not been altered, and its dimensions are
the same as in the E type, but the nickel electrode has been con-
FIG. 73. Section of pencil from the nickel plate of the Edison storage battery
siderably changed. The nickel plate, shown in Figure 72, was
formerly made just like the iron plate, but in the A type it
consists of two rows of 16 round pencils, held in position by a
steel frame. They have flat flanges at the ends by which they
are supported and by which electrical connection is made.
These pencils are perforated nickel-plated steel tubes filled with
the active material, 0.65 centimeter in diameter and 10.5 centi-
176 APPLIED ELECTROCHEMISTRY
meters in length. They are put together with a spiral seam to
resist expansion, and each cylinder also has eight steel rings
slipped over it as a further precaution. The graphite is re-
placed by nickel made into thin flakes, and distributed in
regular layers through the active material, as shown in Figure
FIG. 74. Containing can of the Edison storage battery
73, a section of a pencil taken through its axis. The dark
layers are nickel flake, and the light-colored layers are the ac-
tive material. A pencil contains about 350 layers of each kind
of material, each layer of active material being about 0.01 inch
As in the earlier battery, the containing can is of nickel-
THE EDISON STORAGE BATTERY
plated steel, as shown in Figure 74. The top of the can is
permanently put in place after the plates are in position.
There are four openings in the top, two of which are for the
terminals bolted to the groups of positive and negative plates,
while the third is for filling, and the fourth contains a valve
which allows the gas to escape, but which does not allow any to
enter from the outside. The valve is covered with a fine wire
gauze to hold back any particles of water coming off with the
gas during charging.
The batteries are now made in five sizes. Table 19 gives
the principal facts regarding these cells : 3
No. OF POSI-
PUT. AMP. II RS.
WT. OF ONE
The average discharge voltage for any type is 1.2 volts, when
discharged to 1 volt. As will be explained below, the capacity
can be considerably increased by overcharging. According to
the catalogue of the Edison Storage Battery Company, the
normal capacity of these cells can be increased 30 per cent when
charged at the normal rate for ten hours. The continuous rate
of discharge may be 25 per cent above the normal rate without
injury, and for occasional short intervals it may be four times
the normal rate. A cell may stand unused for any length of
time without injury, but it is said to be better to leave it dis-
charged in this case. As stated above, this must never be done
in the case of a lead storage cell.
8 Catalogue of the Edison Storage Battery Company, and a private communi-
cation from Mr. Holland, of this company.
178 APPLIED ELECTROCHEMISTRY
2. THEORY OF THE EDISON STORAGE BATTERY l
The active material of the nickel plate when first manufac-
tured consists of green precipitated nickelous hydroxide com-
pressed in a steel pocket under hydraulic pressure. Since it
has been found that when nickelous hydroxide is oxidized
chemically, it always first changes to nickel peroxide, NiO 2 , it
is assumed that the same is true of electrolytic oxidation. This
assumption is justified, for it offers an explanation of the behav-
ior of the nickel plate that is in agreement with all of the facts.
When the nickelous hydroxide is electrolyzed as anode in a
potassium hydroxide solution, it therefore first changes to
nickel peroxide. In fact, analysis shows that a freshly charged
plate contains as much more oxygen than corresponds to the
formula Ni 2 O 3 as would correspond to at least 8 per cent of
nickel peroxide. The nickel peroxide then reacts on the nickel-
ous oxide as follows :
NiO 2 +NiO = Ni 2 O 3 , (1)
or if no nickelous oxide is in immediate contact with it, it
decomposes of itself :
2NiO 2 = Ni 2 3 + 0. (2)
Analysis showed that the charged nickel plate,. when dried
over sulphuric acid, has the composition represented by the
formula Ni 2 O 3 1.3 H 2 O to Ni 2 O 3 - 1.1 H 2 O. Any nickel
peroxide originally in the plate therefore disappears on drying.
It is of course impossible to tell from this whether the nickel
oxide is combined with more water before drying or not. In
the hydrates given above, the ratio of atoms of nickel to moles
of water is 1 : 0.55 to 1 : 0.65, while after the discharge the ratio
is 1 : 1. The nickel plate therefore takes up water on discharg-
ing, assuming that the oxides have the same amount of water
in combination while in the potassium hydrate as after drying.
The nickelous compound formed when the nickel plate dis-
charges would 'then be Ni(OH) 2 .
The potential difference between a freshly charged nickel
1 F. Foerster, Z. f. Elektroch. 13, 414, (1907). The discussion of the nickel
plate is taken from this article, except where the contrary is stated.
THE EDISON STORAGE BATTERY
plate and a 2.8 normal solution of potassium hydrate is 0.88
volt, referred to the dropping electrode as zero. The negative
sign refers to the charge on the solution surrounding the elec-
trode. In 50 minutes this potential difference falls to 0.86
volt and in 61 days to 0.75 volt. Analysis of this plate
showed the nickel oxide to correspond to the formula Ni 2 O 3 .
It was also found that the potential difference of an electrode
covered electrolytically with nickelic oxide was 0.77 volt.
This constant potential reached by the charged plate on stand-
ing therefore corresponds to nickelic oxide, and the potential of a
freshly charged plate must be due to the nickel peroxide. The
peroxide is not stable, but gradually decomposes with the
evolution of oxygen, changing to nickelic oxide, and this ex-
plains the constant potential arrived at. There is no sudden
change when all the nickel peroxide is used up, consequently
AMPERE MINUTES, CHARGE
25 20 15
15 20 25
AMPERE MINUTES, DISCHARGE
FIG. 75. Potential of nickel electrode on charge and on discharge
180 APPLIED ELECTROCHEMISTRY
the nickel peroxide and nickelic oxide must form one phase,
such as a solid solution. This evolution of oxygen is the cause
of the loss in capacity on standing, amounting to 10 per cent
in 24 hours, for in this battery the capacity is determined by
that of the positive plates.
The change in the potential of the nickel electrode on dis-
charging is shown by the curve in Figure 75. It is of course
similar to the discharge curve of the whole battery, since the
capacity is determined by this plate. The first part of the
curve, concave upwards, is due to the discharge of the solid
solution of nickel peroxide in nickelic oxide, as is shown by
the fact that this part of the curve entirely disappears if the
battery stands idle for twelve hours after charging. The drop
towards the end of the discharge of 0.55 volt was shown by
analysis to be due to an oxide of nickel lying between Ni 2 O 3
and NiO, possibly Ni 3 O 4 , as this oxide is known to exist. This
second constant potential becomes shorter as the current density
increases, and finally disappears altogether.
The charging potential of the nickel plate is more above the
potential corresponding to nickelic oxide than the discharge
curve is below. This is because the first action in charging
is to produce nickel peroxide, which requires a potential at
least equal to that of a solid solution of nickel peroxide. The
nickel peroxide at first finds a large amount of nickelous oxide
which it oxidizes to nickelic oxide. The nickel peroxide there-
fore disappears rapidly at first, and with a low current density
the potential of the plate is not much above that of nickelic
oxide. Gradually, however, the peroxide becomes more con-
centrated and the potential rises. The nickel peroxide then
begins to decompose with the evolution of oxygen, until its
rate of decomposition equals its rate of formation. Nickel
peroxide is formed also by the electrolytic oxidation of nickelic
oxide, so that its formation continues even after all of the
nickelous oxide ha?s been oxidized.
The efficiency of charging the nickel plate is determined by
the amount of oxygen evolved. The curves in Figure 76 show
this efficiency for three different current densities, when the
THE EDISON STORAGE BATTERY
discharge was stopped before the second stepwas reached. It
is evident from these curves that the full capacity cannot be
obtained without a loss in the current efficiency. This is quite
different from the lead storage battery, in which the efficiency
of charging is nearly 100 per cent throughout the whole charge,
and then suddenly falls to zero at the end. In speaking of the
current efficiency in an Edison storage battery, the capacity
must therefore also be given.
The Negative Plate. The negative or iron plate when
charged consists of finely divided metallic iron in the active
state. If iron is reduced at a high temperature by hydrogen
0.4 0.5 0,6
FIG. 76. Efficiency of charging the nickel plate
and then placed in potassium hydrate, it remains inactive, but
after electrolyzing for a short while as cathode in a potas-
sium hydrate solution it becomes active and has considerable
The iron electrode also has two stages in its discharge, 8 as
seen in Figure 77. The first consists in the oxidation of iron
to ferrous oxide. 2 The second step is due to the oxidation
of ferrous to ferric iron, due to the iron becoming passive
and the velocity of the oxidation of metallic iron becoming too
2 F. Foerster and V. Herold, Z. f. Elektroch. 16, 461, (1910). The discussion
of the iron electrode is taken from this article, where the contrary is not stated.
3 M. W. Schoop, Electrochem. Ind. 2, 274, (1904).
slow. The oxidation of iron to ferrous hydrate is then replaced
partly or entirely by the oxidation of ferrous to ferric iron. If
the ferrous hydrate is not supplied rapidly enough by electro-
chemical oxidation, the metallic iron is oxidized to the ferrous
state by the ferric iron. The result of the second step is, there-
5 10 15 20 25 30
FIG. 77. Potential of iron electrode on discharge
fore, to change metallic iron to the ferric state. In a 2.85
normal solution of potassium hydrate the potential of the first
process is + 0.60 volt referred to the dropping electrode as
zero, the positive sign referring to the charge on the solution
surrounding the electrode. The potential difference between
the ferro-hydroxide electrode arid a 2.85 normal potassium
hydrate solution is + 0.47 volt. This difference in voltage
between the two steps for the iron electrode is therefore only 0.13
volt, while in the case of the nickel electrode it is 0.55
volt. This second step is of no practical importance, for the
iron plate would not reach it when its capacity is greater than
The effect of the addition of mercury to the iron plate is
to increase its capacity by keeping the iron in the active state.
The beneficial effect of mercury was discovered by Edison
empirically, but just how it keeps the iron active is not yet
understood. The mercury makes it possible, however, for the
plate to have a constant capacity for the first step, independent
THE EDISON STORAGE BATTERY 183
of the current density, and is therefore of great practical impor-
tance. It has no effect on charging. The reason for making
the capacity of the iron plate greater than that of the nickel is
that the iron electrode should never be discharged as far as the
second step, for ferric iron cannot be completely reduced again,
and the plates lose in capacity. It has an equally bad effect
to allow the iron plate to stand unused in potassium hydrate
exposed to the air or to allow it to stand in the air when moist.
In charging, hydrogen is liberated on the iron plate from the
start, so that the iron plate causes a greater loss in current than
the nickel, on which no gas is liberated during the first part of
the charge. It was shown above that the nickel plate changes
from Ni 2 O 3 -1.2 H 2 O to Ni(OH) 2 on discharging, and the iron
plate from iron to ferrous hydrate. These changes may be rep-
resented by the equations : 4
Ni 2 3 1.2 H 2 + 1.8 H 2 ; 2 Ni(OH) 2 + 2 OH- + 2 F (3)
and Fe + 20H-^>Fe(OH) 2 -2F. (4)
The sum of these equations is
Fe + Ni 2 O 3 - 1.2 H 2 O + 1.8 H 2 O ^ 2 Ni(OH) 2
+ Fe(OH) 2 +. (5)
This equation represents the final result in the whole cell on
discharge, when taken from left to right, and on charge, w r hen
taken from right to left. These equations are not reversible in
the ordinary sense, however, for they do not show that hydrogen
and oxygen are evolved on charging or that the nickelous
hydrate is first oxidized to nickel peroxide. The Edison cell is
therefore not strictly reversible, and the equations, though
written as reversible, are to be taken only as referring to the initial
and final states of the cell. It is also to be noticed that in adding
the two equations for the iron and the nickel plates the two
quantities of electricity, 2 F, cancel out. This means the two
quantities neutralize each other, thereby producing the current.
The Electrolyte. From the equation (5) it is evident that
water is taken up from the electrolyte on discharging by the
plates and is given up again on charging. This can be seen by
* Foerster, Z. f. Elektroch. 14, 285, (1908).
184 APPLIED ELECTROCHEMISTRY
the change in level in the solution on charging and discharging.
According to equation (5), 0.9 mole of water would be com-
bined or set free to one faraday of electricity passing through
the cell. Other experiments made for the purpose of deter-
mining this quantity gave an average of 1.45 moles of water.
This agreement is not all that could be desired. There is no
question, however, that water is removed from the solution on
discharging, and it therefore follows that the electromotive
force of the battery will decrease with the increasing concentra-
tion of the electrolyte. This is verified by the measurements
of the following table : 4
NORMALITY OF HYDRATE SOLUTION
E. M. F. OF CELL
From what has preceded, it will be evident that the current
efficiency and capacity depend on each other. If the battery
is not fully charged, the current efficiency will be high, but the
full capacity is not obtained. This can be obtained only by
charging after gas evolution has begun, which reduces the
current efficiency. When the cell was charged and discharged
at the normal rate of 4 hours, the ampere hour efficiency was
about 75 per cent, and the voltage efficiency about 70 per cent,
making the energy efficiency about 50 per cent. 6
5 Kennelly and Whiting, Trans. Am. Electrochem. Soc. 6, 146, (1904).
THE ELECTRIC FURNACE
1. GENERAL DISCUSSION
THE electric furnace industries are at present in a state of
rapid development. This is due partly to the manufacture of
a large number of new products made possible by the high
temperature attainable in the electric furnace, and partly to
improved methods in the manufacture of products previously
obtained by other methods.
The electric furnace was probably first used on a commercial
scale by the Cowles Brothers in 1884 in their manufacture of
aluminum alloys, but the rapid increase in its use began about
1893 with the production of calcium carbide, carborundum, and
In the manufacture of many electric furnace products, heat
at a high temperature is the form of energy that brings about
the change desired. The question naturally arises, how is it
possible that it should be economical to obtain heat from such
an expensive form of energy as electricity. There are several
reasons why it is economical. In the first place, the temper-
ature required for the formation of many electric furnace prod-
ucts is above that attainable by any commercial fuel. In such
cases it is evident that if the product is to be formed at all, it
must be formed in an electric furnace. On the other hand, it
has been found economical to use heat generated from electricity
in cases where fuel was formerly used. This is due to a simplifi-
cation in the apparatus and a saving of time and labor. While
electric heat costs more per unit, it may be possible to reduce
the time during which it has to be applied to such an extent
186 APPLIED ELECTROCHEMISTRY
that the quantity of heat required is so much less than when
fuel is used that it more than saves the extra cost per unit.
This is often the case on account of the fact that electric heat
is generated inside the furnace or container just where it is
wanted, while in the use of fuel the heat is generated outside
the furnace and has to penetrate the walls before reaching the
material to be heated. It is evident that more heat will be lost
in the latter than in the former process.
In those furnaces in which the electricity flows through a
core especially made for the purpose and not through the
charge itself, the temperature to which the core is raised is one
of the factors that determines the time required to bring the
charge up to the desired temperature, since the flow of heat
between two bodies is proportional to their difference in tem-
Furnaces may be divided into three classes : arc furnaces,
resistance furnaces, and induction furnaces. In the first, as the
name indicates, the source of heat is an arc. A solid body to
be heated is placed near the arc and is heated by radiation.
By adjusting this distance the temperature to which it is raised
may be regulated. In case a gas is to be heated, the passage of
the arc through the gas itself brings about the desired result.
In the resistance furnaces the current generates heat by passing
some suitable resistor. It is evident that arc furnaces are simply
resistance furnaces where the resistor is a gas; but nevertheless
this distinction is a convenient one. Resistance furnaces may
be of two kinds, first, those in which the current passes through
the charge to be treated and develops heat in consequence of the
resistance of the charge, and second, those in which the current
passes a resistor surrounded by the charge. The latter furnace
is used in those cases where the charge itself does not conduct
well. The first class of resistance furnace may be divided into
two classes, in which (1) the thermal effect is alone active, and
(2) in which electrolysis also takes place.
The induction furnace is the latest type, and is used in the
steel industry. The metal to be heated forms the secondary
winding of a transformer, and forms a closed ring in an annular
THE ELECTRIC FURNACE 187
crucible. A current is induced from the primary winding
sufficiently great to melt the metal.
The following table summarizes this classification.
1. 2. 3.
Arc Resistance Induction
1. The charge con- 2. Current conducted
ducts the current. by a special resistor.
1. Withelec- 2. Without elec-
2. ELECTRIC FURNACE DESIGN
In spite of the fact that the heat is generated inside the furnace,
there is always some heat lost by conduction through the walls
of the furnace, through the electrodes, and in some cases by
hot gases. To increase the economy of furnaces these losses
must be made as small as possible. The case when the loss is
due to gases requires no special consideration, but it will be
desirable to consider the losses through the walls and the
If H equals the number. of calories conducted in one second
through a wall of cross section S, thickness I, and specific con-
ductivity &, when the difference in temperature of the two
faces is T and no heat is lost through the ends of the walls,
In the case of a furnace, the cross section of the wall is not
constant, but increases from the inner to the outer surface.
Generally in making this calculation the average cross section
is taken. Where the walls are thin, this is fairly accurate, but
with thick walls a very great error may be introduced. 1
1 Carl Hering, Trans. Am. Electrochem. Soc. 14, 215, (1908). The discussion
in the text is taken from this article.
188 APPLIED ELECTROCHEMISTRY
For a complete sphere, inner surface s, outer surface S, and
thickness of wall I, the heat conducted per second for unit dif-
ference of temperature is 2
where D is the outside and d the inside diameter. For a cube
where D is the length of the outer edge and d that of the inner
edge. For a cylindrical shell of length (7, thickness of wall Z,
outside diameter 2>, and inside diameter c?,
2 The derivations of this and the following formulae, not given by Bering in
the article referred to, are very simple. The resistance of a spherical shell of
thickness dx, where the radius of the shell is x, is
dE = , if r specific resistance.
4 7TX 2
Integrating between the limits x = ai and x 2 , where a\ and 2 are the inner
and outer radii respectively,
T-J T f Ct2
But if 8 is the outer surface and s the inner, #=4 7ra 2 2 , s=4 IT i 2 , and 2 i =
the thickness of the shell. Substituting these values,
To get the formula for the cylinder of length O all that is necessary is to integrate
dE= between x = a 2 and x = ai,
giving JR^-^- log, 2S.
^ TTO (Zl
For the cubical frustum
dB = r** , whence 7?= - r f ^A = -iL = H,
wx 2 n V ai2 / Vs^ ^-D
where n is given by the equation S=
THE ELECTRIC FURNACE
The curves in Figure 78 give an idea of the error that would
result from using the mean value of the cross section in place
of the above formulae. As abscissae are taken the thickness of
wall in terms of the inner diameter or edge, and as ordinates
the conductivity for one degree difference in temperature and
for a substance whose specific conductivity is one. The dotted
FIG. 78. Heat loss as function of thickness of walls
lines show the conductivity as given by the approximate formula,
and the full lines show the true value. It is evident that the
greatest errors occur in the cases of the cube and sphere,
where they are quite appreciable when the thickness of the
wall equals one half the diameter or one half the inner edge.
In Table 20 the values of the heat conducted through the walls
of the three typical furnaces are collected, which are those given
in the plot. 3 The conductivity and difference in temperature
are assumed unity.
Heat Conductivity of Spherical, Cubical, and Cylindrical Furnaces
The following example will show how this table may be used
in the case of a furnace of one of these types. Let the inner
diameter of a spherical furnace be 15 inches, the thickness of
wall 9 inches ; to find the heat conductance if the wall consists
of infusorial earth whose specific heat conductivity is "k = 0.001
in gram calorie cubic inch units, and if the difference in tem-
perature between the inside and outside face is 700 C. The
8 Hering, I. c. In the original table four and five places of significant figures
are given. Since the specific conductivity of refractory substances at high tem-
peratures is not known to more than two places, only three places are here
THE ELECTRIC FURNACE
thickness in terms of the diameter is -= = 0.6. Opposite
0.6 in the table the conductance is 11.5. This number evi-
dently must be multiplied by c?, &, and 700, giving a loss of 121
grams calorie per second. On the other hand, if the loss is
given and the temperature difference and conductivity are
known, the corresponding thickness can be found.
In the case of the cylinder, the conductivity calculated is for
the cylindrical part alone. These values must therefore be
multiplied by the length of the cylinder, but not by the inside
diameter, and the loss at the two ends must be added.
Unfortunately heat conductivities of refractory substances
are not accurately known above 1000 C. Recently, however,
the mean conductivities between room temperature and 1000 C.
of a number of refractory substances have been determined un-
der the direction of Le Chatelier by Wologdine. The results 4
have been collected by Queneau in Table 21. Data are also
Conductivity of Refractory Materials
Gram Calorie per Cm. Cube
per 1 C. Diflf. in Temp.
Relative Conductivity in Per
Cent of Value for Graphite
Carborundum brick ....
Silica brick ....
Infusorial earth brick . . .
Electrochem. and Met. Ind. 7, 383, (1909).
192 APPLIED ELECTROCHEMISTRY
given in the same article on the porosity and gas permeability
of these materials.
The principal refractory substances for electric furnaces are"
carbon, carborundum, and siloxicon. 5 The use of siloxicon is
limited to temperatures below that at which it is converted
into carborundum, and of carborundum to temperatures below
which it breaks up into silicon and graphite. These sub-
stances all have a higher thermal conductivity than the other
less refractory materials, as seen in the above table, and for
this reason it is usual to build furnace walls in sections, with
highly refractory material inside, where the temperature is
highest, and with material offering a high resistance to the
passage of heat outside. Carborundum, for instance, is one
of the most refractory materials, but as seen from the table
its conductivity is high. It would, therefore, be well to use
this as a lining of such a thickness that the temperature on the
outside of the lining would not be too high for some material
with a lower heat conductivity, such as fire brick or infusorial
earth. Knowing the dimensions, the total loss in power, and
the conductivity, the temperature of the cool side of the lining
is easily calculated. 6
The loss of heat due to conductance through the electrodes
will next be considered. This loss is made up of two quanti-
ties, the heat generated in the electrode by the passage of the
current and the heat which would flow from the hot to the cold
end if the temperature at the hot end were maintained without
passing a current through the electrode. The following dem-
onstration 7 will show how the total heat loss due to the elec-
trodes is related to these two losses, and how electrodes should
be proportioned to make this loss a minimum.
In Figure 79, let ab be a conductor of heat and electricity
imbedded, except at its ends, in a perfect insulator of heat and
electricity. Let the temperature at a be T C. and at 6, C.
5 FitzGerald, Electrochem. and Met. Ind. 2, 349, (1904).
6 For examples see Hering, Electrochem. and Met. Ind. 7, 11, (1909).
7 Hering, Trans. Am. Electrochem. Soc. 16, 287, (1909) ; also Electrochem.
and Met. Ind. 7, 442, (1909).
THE ELECTRIC FURNACE 193
Let a current also ^ JH
pass through the ^ K?TT*T"T!T^f?.T^ ; *
electrode. The ^
problem is to find
the quantity of FlQ 79
heat flowing out
the cold end, when a steady state has been reached.
Let X total energy in watts pressing out of the cold end.
x = energy passing any cross section at distance I from the
H= number of watts that would flow from the hot to the
cold end were there no current.
h number of watts entering the hot end.
W= number of watts generated by the current in the
w = where L = total length of electrode.
T= total fall in temperature from hot to cold end, when
cold end is at 0.
t = temperature at any length I from hot end.
L = total length in centimeters.
I = any distance from hot end.
S = cross section in square centimeters.
k = mean heat conductivity for the given range of temper-
ature in gram-calorie centimeter centigrade degree
r = mean electrical resistivity for the given range in ohms
for a cube of one centimeter edge.
1= current in amperes.
R = total resistance.
j is the factor 4.19 by which a given number of calories
per second is multiplied to change to watts.
Let dl be an infinitely short section at distance I from the
hot end, and let the heat flowing into this section be x. The
heat generated in the section by the current will be
194 APPLIED ELECTROCHEMISTRY
Also .-/feS (2)
where is the heat gradient at I.
Differentiating this gives
and eliminating dx between equations (3) and (1)
d?t = w_ Pr
dl* jkS JkS*
Since r and k are functions of , to be strictly accurate these
quantities should be expressed as such before integrating. For
the sake of simplicity, however, mean values for r and k for the
temperature interval considered are taken, and these quantities
in equation (4) are treated as constants. Integrating once
under this assumption gives
TJ = a ~~ "v"? '
and a second time
In this equation a and b are determined by the fact that when
Z = 0, t=T, and when l=^t = Q.
Substituting these values in (6) gives
Substituting this value of a in (5) and the value of thus ob-
tained in (2) gives
This equation states that the energy passing any given cross
section is equal to the energy that would pass were no current
flowing, minus one half the PR energy, plus the PR energy
generated in the hot end. When L = l, since wL = W,
THE ELECTRIC FURNACE 195
This states that the energy passing out the cold end as heat
equals the energy that would pass out when no current is flow-
ing, plus one half the I^R energy.
Suppose that in (7) I = 0, then x h and h = If -- - . In
order that no heat shall enter the hot end, h = 0, whence
ff= . The last equation states that if no heat enters the hot
end from the furnace, the heat flowing from the hot to the cold
end of the electrode if there were no current equals ^ I*R.
Now the product of H x - =? - , which is independent of S
and L. When the product of two variables is a constant, their
sum is a minimum when the two variables are equal; that is, in
the equation JT= H-\ -- , X will be a minimum when H= ->
or the minimum loss = I^R. Substituting the values of H and
W in H = , we have the equation
Solving this for
y = 0.346jfy-^-, (9)
and substituting this value in the equation (8),
If, in place of using mean values of the specific heat conductiv-
ity and electrical specific resistance, the variable values 8
k t = & (1 + at)
and r t = r (l + a^)
are substituted in the formulse above, the following results are
8 H. C. Richards, Trans. Am. Electrochem. Soc. 16, 304, (1909).
5 a \ ~ 3 a
The errors introduced by using mean values of k and r and
treating them as constants will be small unless the temperature
coefficients are enormous.
As was shown above, the minimum loss of one electrode is
J?R or le. Substituting this in (10),
e = 2.89V&r2 r . 0-1)
This voltage is seen to be dependent only on the thermal con-
ductivity, electrical re-
sistivity, and tempera-
ture difference of the
ends of the electrodes,
which means that for
every material there is
a characteristic mini-
mum drop of potential
in the electrodes for
one degree difference
in temperature below
* which it is not possible
to go without increas-
ing the loss. This
minimum drop in
potential has been called the electrode voltage.
The temperature distribution in the electrode is given by the
T * Ct .'7_* Ct '1. O'
obtained from equation (6) by substituting in the values of a
and b. The variables being t and Z, the curve is evidently a
parabola. If no current flows, w = and the equation becomes
the straight line ceb in Figure 80.
THE ELECTRIC FURNACE 197
Making T=Q gives t = o"Vy ' ^e P ara bola p. To find
the temperature distribution for minimum loss, solve for T in
the equation JKT = , and substitute in (12), obtaining
the parabola P. When - is greater or less than H, the tem-
perature distribution is given by P f or P" respectively.
In any problem involving the design of electrodes, the tem-
perature difference between the hot and cold ends of the elec-
trode and the kilowatts to be absorbed in the furnace will be
given. From the value of the power the voltage would then
be made as high and the current as low as practicable. From
formula (9) compute the proportion of the section to the
length. The length, which should be as short as possible,
will be determined by the thickness of the walls of the fur-
nace. Having fixed the length, the section is then obtained
from the ratio of the section to the length. The two remain-
ing factors which must be known are the values of the heat
and electrical conductivities of carbon and graphite, the only
two substances used for electrodes in resistance furnaces.
These values have not yet been determined accurately for high
temperatures, but the mean values have been determined by
Bering between 100 C. and 900 C. 9 The method of deter-
mining heat conductivity depends on the demonstration above.
If in equation (13) Z=0, then t= ^and k=
In order to measure &, a conducting rod of length L and sec-
tion S, embedded in a nonconducting material, is heated by a
measured amount of electrical energy and the temperature T
measured at the center. In order to have no heat pass out the
sides of the rod, it is surrounded by a number of similar rods
at the same temperature as the one measured. The electrical
conductivity is obtained from the ammeter and voltmeter read-
9 Trans. Am. Electrochem. Soc. 16, 317, and 315, (1909).
ings and the dimensions. The values in Table 22 have been
obtained by this method. 9 The units are centimeters, gram
calories, and ohms, and centigrade degrees.
BETWEEN 100 C. AND
The accuracy of these figures is estimated at a few per cent.
The electrode voltage (equation (11)) from these data for one
degree for graphite is 0.0447 and for carbon is 0.0639, which
means that the minimum loss for carbon is about 50 per cent
greater than for graphite. Later measurements by Hering 10
gave results from which the following Table 23 has been com-
puted. The values of heat conductivity and for electrical
resistivity are for centimeter cubes.
10 Trans. Am. Electrochem. Soc. 17, 166, (1910).
THE ELECTRIC FURNACE
The following data were obtained by Hansen. 11 The units
are the same as in the table above.
NATIONAL CARBON Co.'s ELECTRODES
3200 and 200
2830 and 30
3500 and 30
The electrical and thermal conductivities of carbon elec-
trodes cannot be determined above 1600, because on cooling
the values do not come back to the original ones, due to a par-
tial conversion of the carbon into graphite. 11
Besides the loss in the electrode itself, a large loss occurs at
the contact between the electrode and the cable, due to the
contact resistance. This resistance varies with the current
density, and where brass clamps are used on graphite it
amounts to 0.0117, 0.0045, and 0.0039 ohms per square centi-
meter for current densities of 3.7, 5.6, and 7.4 amperes per
square centimeter. 11
With the aid of the constants above, a numerical example
may be given. Let the capacity of the furnace be 500 kilo-
watts, the current 10,000 amperes, and the temperature 1700 C.
inside and 100 at the cold end of the graphite electrode.
Assuming r = 0.000820 and k = 0.291, by formula (10),
X= 17.8 kilowatts for each electrode. Assuming for carbon,
r = 0.00276 and Jc = 0.129, X= 21.8 kilowatts. Of course, the
cross sections of the graphite and carbon electrodes are not
equal for equal lengths.
11 Trans. Am. Electrochem. Soc. 16, 329, (1909).
200 APPLIED ELECTROCHEMISTRY
The discussion so far has been for the case that the dimen-
sions of the furnace and the power to be applied in order to
bring about a desired result are known. If these are not
known, an experiment would usually be made on a small scale
in order to determine the relation between the size of fur-
nace and the power. There are two cases to be considered,
(1) when there is a central core for carrying the current,
and (2) when the charge to be heated itself carries the
In the first case the heat has to be conducted from the core
to the surrounding charge. 12 The rate of this flow is propor-
tional to the difference in temperature of the core and the sur-
rounding charge, the thermal conductivity of the charge, and
the surface area of the core. If heat is generated in the core
at a given rate, the temperature to which it will rise in a given
time will depend on the specific heat of the core and the rate
at which the heat flows into the surrounding charge. This
rate of flow depends on the area of the core and the conduc-
tivity of the charge. Suppose that to bring about the desired
reaction in a given charge with a core of a given material ex-
periments are made with a small furnace until the conditions
are found under which the desired reaction is brought about.
This means that a definite amount of heat must pass per unit
surface of the core, which is a constant for these materials and
is independent of the dimensions. If the voltage is E and the
current J, the energy in watts per unit surface is a = - >
when P is the radius and L the length of the core. Collecting
the constants in one factor, this may be written PL = AEI.
If r is the specific resistance of the core, we also have
XT T T
= = B . For any furnace of any other dimensions
L v and P v the voltage and current E l and I are given by the
equations P^ = AE^ and -1=1? 1. From these equa-
tions we could solve for the new values E and I v if L 1 and P 1
M FitzGerald, Electroc-hem. and Met. Ind. 2, 342, (1904).
THE ELECTRIC FURNACE 201
are given. Usually, however, the power is given, and the
proper dimensions L^ and P l are desired. Solving for these
quantities, P 1 =
and , A
The following is an example of the use of these formulae. It
was desired to design a 200-kilowatt furnace using a current
of 4000 amperes and 50 volts. Experiments on a small scale
showed that the right conditions were obtained with 200 am-
peres at 100 volts and a core 365 centimeters long and 5.1 cen-
timeters in radius. From these values the proper length and
radius for the large furnace are found to be 495 centimeters
and 37.6, respectively.
For the second case, where the current passes through the
charge itself, it is simply necessary to know the amount of heat
required to raise a given mass to the desired temperature, that
is, the number of watts per unit mass. If the specific heat of
the charge is known, this can be computed ; if not, an experiment
on a small scale with a given mass will determine the energy
PRODUCTS OF THE RESISTANCE AND ARC FURNACE
1. CALCIUM CAKBIDE
THE discovery of calcium carbide is due to Wohler, 1 who
prepared it by the action of carbon on an alloy of calcium and
zinc. Even previous to Wohler, E. Davy had also produced it
in an impure state without identifying it. 2 The commercial
importance of calcium carbide, however, dates from its redis-
covery by Thomas L. Willson, 3 which was nearly simultaneous
with that of Moissan (1892).
The reaction between lime and carbon by which calcium
carbide is produced is the following :
As indicated, this is a reversible reaction, and according to the
Phase Rule has one degree of freedom ; that is to say, at a given
temperature there is one definite pressure of carbon monoxide
which corresponds to equilibrium. At 1475 C. this pressure
has been found to be 0.82 millimeter of mercury. 4 Above
1500 calcium carbide decomposes into its elements, but of course
not as rapidly as it is produced, otherwise its manufacture
would be impossible.
When calcium carbide is formed from calcium and diamond,
7250 calories are absorbed at room temperature. When formed
from lime and carbon, 121,000 calories are absorbed at room
temperature, and the temperature coefficient of the heat of the
1 Ann. d. Chem, und Pharm. 125, 120, (1863).
2 Lieb. Ann. 23, 144, (1836). See Abegg, Handbuchder anorganischen Chem.
2, 119. 8 Lewes, Acetylene, p. 24, (1900).
4 Thompson, Proc. Am. Acad. 45, 431, (1910) ; also Met. and Chem. Eng. 8,
PRODUCTS OF THE RESISTANCE AND ARC FURNACE 203
reaction has been calculated to be 3.3 calories per degree. 6 The
fact that heat is absorbed when the above reaction proceeds
from left to right shows that the equilibrium pressure of carbon
monoxide increases with the temperature, and it can be calcu-
lated that at about 1840 the pressure equals one third of an
atmosphere. If carbon were heated in the presence of air much
above red heat, all the oxygen would be converted to carbon
monoxide, and if none escaped, its resulting partial pressure
would be one third of an atmosphere. It would therefore be
necessary to heat carbon and lime to a temperature above 1840 C.
before carbide could be formed. In actual practice, however,
the partial pressure of carbon monoxide would be less than one
third of an atmosphere, in which case carbide could be formed
at a lower temperature. Taking these facts into consideration,
it does not seem probable that 2000 C. is exceeded in actual
practice, for high temperature would accelerate the decomposi-
tion of the carbide already formed. This explains the fact that
a resistance furnace, in which the temperature is lower than in
the arc, gives better yields than an arc furnace. 6
Commercial calcium carbide is dark colored and crystalline
but if pure it is colorless and transparent. 7 It has a density at
18 of 2.22, and is insoluble in all known solvents. It is a
powerful reducing agent. If heated with metallic oxides it
gives, according to circumstances, an alloy of the metal in
question with calcium or the metal itself, probably according
to the reaction. 7
3 M 2 + CaC 2 = CaO + 3 M 2 + 2 CO
or 5 M 2 O + CaC 2 = CaO + 5 M 2 + 2 CO 2 .
It further has the property of absorbing nitrogen according to
CaC 2 + N 2 =CaCN 2 + C,
forming calcium cyanamide. This is an important method of
fixing atmospheric nitrogen, and will be referred to later under
6 Thompson, Trans. Am. Electrochem. Soc. 16, 202, (1909).
6 Tucker, Alexander, and Hudson, Trans. Am. Electrochem. Soc. 15, 411,
(1909). 7 Abegg, Handbuch der anorganischen Chem. 2, p. 121.
The principal use of calcium carbide is to produce acetylene
for illumination. This gas is evolved when the carbide is
treated with water, according to the reaction:
C 2 H 2 .
The first to produce calcium carbide on a commercial scale,
as stated above, was Thomas L. Willson, at the Willson
Aluminum Works at Spray, 8 North Carolina. Willson was
attempting to reduce lime by heating with carbon, hoping to
get calcium with which to try the reduction of alumina. It was
by accident that the material produced was found to react with
water and give off an inflammable gas. Soon after this discovery
Willson's plant at Spray was investigated by Houston, Ken-
nelly, and Kennicutt. 9
Two runs were made with
the purpose of determin-
ing the cost of manufac-
turing calcium carbide
under conditions existing
at that place. There
were two furnaces built
in one structure, as shown
in Figure 81, the walls
and partition of which
were brick, while the
front was only partly cov-
ered by cast-iron doors.
The floor space of each
furnace was 3 by 2J feet.
The furnaces united at a
height of 8 feet into a
single chimney for carry-
ing off the gases. The
base of the furnaces con-
FIG. 81. Carbide furnace at Spray, North
8J. W. Richards, Electrochein. Ind. 1, 22, (1902). The date given by
Richards is 1891. This is evidently too early ; see note 3.
9 Progressive Age, 14, 173, (April 15, 1896). (Published at 280 Broadway,
New York City.)
PRODUCTS OF THE RESISTANCE AND ARC FURNACE 205
sisted of a heavy piece of iron between, 1 and 2 inches in thick-
ness, 6 feet in length, and 2| feet in
width. The iron plate was completely
covered by two carbon plates between
6 and 8 inches thick. These formed the
lower electrode. The upper electrode
of each furnace was a carbon block 12
by 8 inches in section and 36 inches long,
protected by an iron casting -fa inch
thick. The space between the casting
and carbon was filled with a mixture of
hot pulverized coke and pitch. The
first run lasted 3 hours with an aver-
age activity supplied to the furnace of
144 kilowatts at approximately 100 volts. FlG - 82. - Longitudinal ver-
. tical section of the first car-
ThlS made a total power consumption of tide furnaces at Niagara
432 kilowatt hours, yielding 98.0 kilo- Falls
grams of 79 per cent pure carbide. The second run lasted 2
hours and 40 minutes with an average
activity of 146.7 kilowatts, making the
^ / total power consumption 388.5 killowatt
hours and yielding 87.5 kilograms of 84
per cent carbide. This is about 0.225
kilograms of carbide per kilowatt hour.
The cost of producing carbide at Spray,
working the furnaces 365 days a year and
24 hours a day, was estimated at about
$33 per 2000 pounds of impure carbide.
This estimate, however, is made up of
a large number of items that would be
considerably changed for other places.
The largest producer of carbide in the
FIG. 83. Transverse ver- United States is the Union Carbide Com-
S35?i; p^y. whose W01 ' ks are at Nia s ara Falls -'
ara Falls Their first furnaces were of the Willson
type, in which the lower electrode was a small car which could
be removed, when filled with an ingot of carbide, to make room
for another, as shown in Figures 82 and 83. This type has been
displaced at Niagara Falls by the Horry rotary continuous fur-
nace, introduced in
1898 and shown in Fig-
ure 84. 10 It consists
of an iron wheel 8 feet
in diameter and 3 feet
in width, with an an-
around the circumfer-
ence in which the car-
bide is formed. The
electrodes project ver-
tically down into this
space. Lime and car-
bon are fed in, and as
carbide forms, it is removed from the electrodes by the rotation
of the furnace. Iron plates hold the carbide in place while
under the influence of the current. When the rotation has
carried it to the other side of the furnace, it has had time to
cool, as there is only one complete rotation a day. The outer
plates are then removed, and the carbide is broken off in pieces
6 to 9 inches thick. Each furnace takes 3500 amperes at 110
volts and produces 2 short tons of carbide a day.
FIG. 84. Horry carbide furnace
Sweden .... . . . .
10 Lewes, ibid. p. 207 ; Richards, Electrochem. Ind. 1, 22, (1902) ; Haber, Z. f.
Elektroch. 9, 834, (1903).
PRODUCTS OF THE RESISTANCE AND ARC FURNACE 207
The production of the Union Carbide Company from year to
year has not been made known. The preceding table shows
the estimated output of the world for 1908. u
In 1902 the Union Carbide Company sold carbide to home
consumers at about $70 a ton, but exported it for $50 a ton. 12
In 1907 the price was still $ 70 a ton in this country.
In Europe 13 the form of furnace still used is of the Willson
type. In some cases the ingot is formed on a truck that can be
removed when full, and in others a stationary crucible is used.
In the former case it has been found an improvement to have
two electrodes suspended over the truck, so that the truck is no
longer in the electric circuit. In the case of fixed crucibles the
capacity has been increased in some cases up to 6000 kilowatts,
and a more satisfactory method of tapping has been devised.
Formerly the solid carbide formed around the tap hole had to
be broken away, but the later method consists in inserting an
iron rod connected to the upper electrode into the tap hole,
where an arc is formed between the rod and the solid carbide.
The iron and carbide are both melted by the arc, and an opening
is formed through which the melted carbide can flow out.
With regard to the power required for the production of car-
'bide, the only figures of any practical importance are not those
obtained by calculation, but those obtained in actual practice.
The original plant of Willson produced 5.4 kilos per kilowatt
day of 24 hours 9 of 80 to 85 per cent carbide. At Meran the
yield is 5.8 kilos of 78 per cent carbide per kilowatt day. 14
At Foyers in Scotland the yield per kilowatt day of 24 hours is
4.2 kilos of 87 per cent carbide. 15 At Odda, Norway, it lies
between 4.5 and 5.2 kilograms. 16
The materials 17 used in making carbide are freshly burnt
lime and carbon in the form of anthracite coal, metallurgical
coke, or charcoal. Ordinary gas coke has too many impurities
for this purpose. Charcoal is used only where one of the other
forms of carbon cannot be obtained, as it generally contains
u Min. Ind. 17, 100, (1908). 12 Min. Ind. 11, 76, (1902).
13 See Conrad, Electrochem. and Met. Ind. 6, 397, (1908).
14 Lewes, Acetylene, p. 242. 16 Lewes, I.e. p. 262.
is Electrochem. and Met. Ind. 7, 213, (1909). 17 Lewes, pp. 264-284.
208 APPLIED ELECTROCHEMISTRY
considerable traces of phosphates, which appear in the acetylene
generated from the carbide in the form of phosphureted hydro-
gen. The reaction requires 36 parts of carbon to 56 of lime.
In most ingot carbide furnaces 100 parts of lime to 70 of car-
bon are used. In furnaces from which the carbide is drawn
off in the liquid state a higher proportion of lime is used in
order to lower the melting point of the carbide. This, of
course, has the result of making the carbide less pure.
It was at first supposed that fine grinding of the materials
was necessary, but it has since been found that pieces as much
as one inch in diameter may be used. 18
Carborundum is the trade name for the carbide of silicon,
which has the formula CSi. It was probably first produced
by Despretz in connection with experiments on refractory ma-
terials, 1 in the course of which he heated a carbon rod em-
bedded in sand by passing an electric current through the
rod. He obtained a very hard tube of six times the diameter
of the carbon rod, lined on the inside with quartz in the form
of lampblack. It seems probable that in this experiment some
carborundum was formed, though no mention is made of crystals.
It seems more certain that carborundum crystals were obtained
by R. Sidney Marsden, 2 by heating for several hours silver or an
alloy of silver and platinum in a Berlin porcelain crucible with
amorphous carbon considerably above the melting point of silver
and then cooling slowly for 12 to 14 hours. On dissolving the
silver in nitric acid it yielded from its interior a number of
beautiful crystals of the hexagonal system and varying in
color from light yellow to dark brown, or even black. Other
crystals were found in the form of hexagonal prisms, but these
were in most cases colorless and transparent. The colored
crystals were doubtless crystallized carborundum, formed from
the silica glaze on the crucibles and the amorphous carbon.
18 Blount, Practical Electrochemistry, p. 230, (1901).
1 C. R. 89, 720, (1849).
2 Proc. Royal Soc. of Edinburgh, 11, 37, (1880-1881).
PRODUCTS OF THE RESISTANCE AND ARC FURNACE 209
The white crystals were evidently silica, as they dissolved when
boiled in hydrofluoric acid.
In 1886 A. H. Cowles 3 obtained some hexagonal crystals
from his furnace on attempting to melt quartz. This was an-
alyzed and thought to be a suboxide of silicon. On seeing Ache-
son's Carborundum at the Chicago Exposition in 1893, Cowles
recognized its similarity with his so-called suboxide of silicon.
This resulted in a lawsuit between the Cowles Electric Smelting
and Refining Company and the Carborundum Company. 4 Schut-
zenberger and Colson hacLsuspected the existence of a com-
pound of the formula Si 2 C 2 as early as 1881, 5 and in 1892
Schiitzenberger 6 obtained the amorphous carbide of silicon by
heating together silicon, silica, and carbon, and determined its
composition. Its color was a clear green. Finally, Moissan 7 has
made crystallized carbide of silicon in the following different
ways : 1. Carbon was dissolved in melted silicon between 1200
C. and 1400 C. from which crystals of carbide several milli-
meters long were obtained by dissolving the silicon in a boiling
mixture of concentrated nitric acid and hydrofluoric acid. 2. By
heating silicon and carbon in the proportion of 12 parts of carbon
to 28 parts of silicon. The mass of crystals obtained was easily
purified by first boiling in a mixture of concentrated nitric acid
and hydrofluoric acid and by then treating with nitric acid and
potassium chlorate. The crystals were frequently colored yellow,
but could be obtained completely transparent. 3. By heating a
mixture of iron, silicon, and carbon in the electric furnace, giv-
ing a metallic fusion containing crystals of carbide of silicon.
The excess of iron or silicon was then dissolved. 4. By heating
silica and carbon in the electric furnace. 5. By the action of
the vapor of silicon on the vapor of carbon. This experiment
was made in a small carbon crucible containing fused silicon.
The bottom of the crucible was heated to " the highest tempera-
8 Proc. of the Soc. of Arts for 1885-1886, p. 74, Boston.
4 FitzGerald, Carborundum, in the Engelhardt Mongraphien iiber Ange-
*C. R. 92, 1508, (1881). 6 C. R. 113, 1089, (1892).
7 Moissan, The Electric Furnace, translated by Lehner, p. 274, (1904).
210 APPLIED ELECTROCHEMISTRY
ture of the electric furnace." After the experiment, slightly
colored, very hard and brittle crystals in prismatic needles of
carbon silicide were found. The description of this experi-
ment is far from convincing. If the crystals were found in the
silicon, there is no evidence of the action of one vapor on the
other, but even the original article 8 does not state where
the crystals were found, which would be necessary to decide
In 1891 at Monongahela, Pennsylvania, E. G. Acheson 9 dis-
covered the crystallized carbide of silicon, in carrying out some
experiments with the object of producing crystallized carbon.
The object was to dissolve carbon in melted silicate of alu-
minum, or clay, and by cooling to cause the carbon to crystallize.
The first experiments were carried out in an iron bowl lined
with carbon in which was placed a mixture of carbon and clay.
The mixture was fused by means of an electric current passing
between the bowl and a carbon rod directly over it. On fusion
a violent reaction took place, and after cooling a few bright
blue hard crystals were found. These were first supposed to
be carbon, but later were taken for a compound of alumina or
corundum and carbon, from which the name carborundum was
made up. Subsequent to this it was found that better results
were obtained when silica was used in place of clay, and when
common sodium chloride was added. The reason for this was
evident when the following analysis of the product was made:
Silicon 62.70 per cent
Carbon 36.26 per cent
Aluminum oxide and ferric oxide . . . . . . 0.93 per cent
Magnesium oxide 0.11 per cent
This showed the substance in the pure state to be CSi.
The furnace in which these experiments were carried out
was made of refractory bricks, the interior dimensions being
10 by 4 by 4 inches. The current was carried by a core of
granulated carbon, as shown in Figure 85.
8 C. R. 117, 425, (1893).
8 Journ. of the Franklin Inst. 136, 194 and 279, (1893).
PRODUCTS OF THE RESISTANCE AND ARC FURNACE 211
Figure 86 shows an end view of this furnace and the layers
of different materials after a run. B is a solid mass of sand
FIG. 85. Longitudinal section of Acheson's experimental carborundum furnace
and carbon held together by fused salt. C is chief product of
the reaction, crystallized carbide of silicon. W represents a
white or gray-greenish-looking shell,
and consists of small pieces the size
of the original grains. They are
soft, and may easily be reduced to
fine powder, and are of no value as
an abrasive, though analysis shows
them to be principally carbide of sili-
con. It is amorphous carborundum,
or carborundum fire sand. G- is
, ., , ... , , FIG. 86. Transverse section of
graphite mixed with carborundum, Aches0 n's experimental carbo-
and D is the core, only , portion of rundum furnace
which becomes graphitized even though used repeatedly. The
output of this small furnace was \ pound a day. 10
The furnaces used at Monongahelainl893 were 18 inches wide,
12 inches deep, and 6 feet long. The core was of granular
carbon in the form of a sheet 10 inches wide, 1 inch deep, and
5J feet long. In 7| to 8 hours a portion of the charge was
transformed into 50 pounds of crystallized carborundum.
On moving to Niagara Falls the furnaces were construe ted as
shown in Figure 87. n The end walls are built of refractory
10 FitzGerald, Journ. Franklin Inst. 143, 81, (1897).
11 FitzGerald, Carborundum, p. 8. .
brick and clay, and carry electrodes, 5 2 , consisting of rectangu-
lar carbon rods clamped together. Contact is made with the
copper cables by the copper plates, > 5 , as shown. A are the
brick side walls of the furnace put together without cement.
D is the mixture, C the core of granulated carbon, and c is fine
carbon powder for the purpose of making contact between the
carbon electrodes and the core. Up to 1907 the total length of
this furnace was 7 meters ; the inside dimensions were, length,
5 meters, width, 1.8 meters, and height, 1.7 meters. The elec-
trodes consisted of 25 carbon rods, 86 centimeters in length,
and 10 by 10 centimeters in cross section. The core was 53
FIG. 87. Longitudinal section of carborundum furnace
centimeters in diameter. A perspective of the furnace in oper-
ation is shown in Figure 88.
The power absorbed by each furnace is 746 kilowatts. The
voltage varies from 210 volts at the start to 75 volts when the
resistance of the core had dropped to its final constant value.
Soon after the current is turned on, carbon monoxide is pro-
duced, due to the oxidation of the carbon in the core and in the
charge. The gas is always lighted, and burns during the run.
When the temperature has become sufficiently high, carbo-
rundum is formed according to the following reaction :
Si0 2 + 3 C = CSi + 2 CO.
The heating lasts 36 hours, and produces 3150 kilograms of
crystallized carborundum, surrounding the core to a depth of
PRODUCTS OF THE RESISTANCE AND ARC FURNACE 213
214 APPLIED ELECTROCHEMISTRY
from 25 to 30 centimeters, This corresponds to 8.5 kilowatt
hours per kilogram, which is a great improvement over the first
furnaces of the Carborundum Company at Monongahela, which
were built for 100 kilowatts, and yielded one kilogram of car-
borundum for an expenditure of 17.6 kilowatt hours. The
present electrical equipment of the Carborundum Company at
Niagara Falls has a capacity of 5300 kilowatts. 12
The raw materials used by the Carborundum Company con-
sist of ground quartz 99.5 percent silica, coke, such as is used
in blast furnaces, sawdust, and sodium chloride. The object
of the sawdust is to make the charge porous to facilitate the
escape of the carbon monoxide. The coke used for the core is
sifted to get rid of the powder; that used for the charge is
powdered. The charge is made up in lots of 500 kilograms, and
has the following composition :
Quartz 261 kilograms
Coke 177 kilograms
Sawdust 53 kilograms
Salt 9 kilograms
In 1907 the furnace plant was remodeled, 13 and the furnaces
were made 9.15 meters long and 3.67 meters wide. These are
presumably outside dimensions. The power absorbed is now
1600 kilowatts with the maximum current 20,000 amperes.
The yield of each furnace in one run is 15,000 pounds, or
6800 kilograms, of crystallized carborundum. On coining from
the furnace the carborundum is ground, treated with concen-
trated sulphuric acid to remove harmful impurities, and is washed
with water. It is then sorted into different sizes.
Table 25 gives the production of carborundum in this country
and its value including the year 1909. 14
12 Electrochem. and Met. Ind. 7, 190, (1909).
13 Min. Ind. 16, 155, (1907); 17, 112, (1908).
" Min. Ind. 18, 86, (1909).
PRODUCTS OF THE RESISTANCE AND ARC FURNACE 215
VALUE IN DOLLARS
1891 . 0.023
1892 ..'..... 1
1893 .'-...-. 7
1895 . 102
1900 . . ' 1089
1906 '. . 2824
In 1902 the cost of manufacture was 4 cents to 5 cents a pound,
and during this year the average selling price was 10 cents a
pound. 15 The only producer in this country is the Carborundum
Company of Niagara Falls. In Europe it is produced at La
Bathie, France, Iserhohn, Germany, and Prague. 16
Carborundum is used principally as an abrasive and as a sub-
stitute for ferrosilicon in the manufacture of steel. In 1902
one third the total output was consumed in this industry. 17 The
abrasive qualities of carborundum are affected by its great
brittleness, on account of which it will not cut diamond unless
reduced to a fine powder. 9 It is made into polishing wheels by
mixing with a certain amount of kaolin and feldspar as a binder,
compressing in a hydraulic press, and burning in a furnace such
as is used in the manufacture of porcelain. Carborundum is
15 Min. Ind. 11, 78, (1902).
"Min. Ind. 11, 227, (1902).
"Mm. Ind. 10, 253, (1901).
also used in wireless telegraphy as a detector, and in a different
form, known as Silundum, 1 * 1 us a resistance for heating purposes.
Silundum is made by exposing rods of carbon to the vapor of
silicon, which penetrates the carbon, changing it to silundum
arid thereby increasing its electrical resistance to a sufficient
extent to make it a good resistor. In the form of bricks car-
borundum is used as a refractory material in building furnaces,
when the temperature to be withstood is very high.
Silicon carbide is colorless when pure, 10 but the commercial
product is black, due either to carbon, iron, or to a" thin film of
silica 19 on the surface. The following analysis is due to Moissan :
Silicon 69.70 69.85 70.00
Carbon 30.00 29.80 30.00
The following is an analysis of Acheson's product : u
Silicon 64.93 per cent
Carbon and oxygen 33.26 per cent
Loss in beating 1.36 per cent
Aluminum 0.25 per cent
Calcium, magnesium, iron .... trace
99.80 per cent
When the same material was purified by hydrochloric acid and
sodium hydrate, by heating in oxygen, and finally by heating
with hydrofluoric acid, its analysis gave the following result :
Silicon 69.10 per cent
Carbon 30.20 per cent
A1 2 O 3 and Fe 2 O 3 0.49 per cent
CaO 0.15 per cent
99.94 per cent
The density is 3.2. The crystals have been found by Frazier
to be rhombohedral. 20 It easily scratches ruby, and, as stated
above, when finely powdered, will polish diamond.
re Boiling, Electrochem. and Met. Ind. 7, 25, (1909).
w Min. Ind. 16, 155, (1907). 20 Journ. Franklin Inst. 136, 289, (1893).
PRODUCTS OF THE RESISTANCE AND ARC FURNACE 217
When carborundum is heated to a sufficiently high tempera-
ture silicon is vaporized, leaving carbon in the form of graphite.
The temperature at which decomposition takes place has been
found by Tucker and Lampen 21 to be 2220 and the temperature
of formation, 1950C. There is hardly a doubt that both the
SiO 2 + 3 C = SiC + 2 CO
and SiC = Si + C
are reversible. The temperature of formation therefore depends
on the partialpressure of carbon monoxide, and the temperature
of decomposition on the partial pressure of silicon vapor, for
according to the Phase Rule each of these systems has one
degree of freedom. These values, however, probably represent
fairly well the temperatures of formation and decomposition in
the Acheson furnace.
Carborundum is not attacked by sulphur or oxygen at
1000 C., 7 but according to Acheson it is oxidized in an at-
mosphere containing considerable oxygen at 1470 C. 22 It is
attacked slightly by chlorine at 600. Fused potassium nitrate
and chlorate, boiling sulphuric and hydrofluoric acids are all
without action. The same is true of a boiling mixture of con-
centrated nitric and hydrofluoric acids. On the other hand it
is attacked by fused potassium hydrate, forming potassium
carbonate and silicate.
3. SlLOXICON 1
There are a number of compounds, besides the carbide of
silicon, that contain carbon and silicon in the same proportions
as the carbide. In 1881 Schiitzenberger and Colson 2 prepared
a compound of the formula SiCO by heating silicon in an at-
mosphere of carbon dioxide. The reaction is stated to be
3 Si + 2 CO 2 = SiO 2 + 2 SiCO.
21 Journ. Am. Chem. Soc. 28, 853, (1906).
22 Electrochem. Ind. i, 373, (1903).
1 The name given by Acheson to compounds of carbon, silicon, and oxygen in
varying amounts. 2 C. R. 92, 1508, (1881).
218 APPLIED ELECTROCHEMISTRY
The same compound was formed at a higher temperature by
the direct union of silicon and carbon monoxide. A compound
of the formula Si 4 4 N was formed in a similar way. On heat-
ing silicon in a stream of hydrogen saturated with benzene at
50 to 60 C. two compounds were obtained, one of the
formula C 2 Si, and the other of a variable composition, but fre-
quently containing more oxygen than corresponds to the
formula CSiO 2 . 3 On heating silicon in a vapor of carbon sul-
phide two compounds deposited in the cold part of the com-
bustion tube corresponding to the formulae SiSO and SiS. In
the boat containing the silicon a greenish powder was obtained
which, when purified by boiling in potassium hydrate and treat-
ing with hydrofluoric acid, had the composition Si 4 C 4 S. This
when heated in a current of oxygen gave Si 4 C 4 O 2 . These
bodies all look alike and can be distinguished only by analysis. 4
They are pale green powders, infusible, unattackable by hydro-
fluoric acid or strong solutions of caustic alkali. Fused caus-
tic alkali decomposes them, giving alkali silicate and carbonate.
They resist oxidation at red heat. It will be seen that these
compounds also resemble the compound obtained by Schiitzen-
berger 4 in 1892, and which analysis showed to be SiC, though
the color of the latter compound is described as a clear green.
It, therefore, seems that carborundum exists in two forms, one
crystalline and the other amorphous, while the amorphous form
has all the appearance of other compounds containing silicon
and oxygen in the same proportions as carborundum, together
with a variable amount of oxygen. From the contradictory
statements 6 found in the literature it seems that the layer of
material which is formed just outside the carborundum consists
of silicon, carbon, and oxygen in varying amounts, and that it
goes by the names of amorphous carborundum, carborundum
8 Colson, C. R. 94, 1316, 1526, (1882).
4 Schiitzenberger, C. R. 114, 1089, (1892).
6 In Min. Ind. 15, 93, (1906), it is stated that another product of the carborun-
dum furnace is amorphous carborundum or carborundum fire sand, and that
siloxicon is a second product obtained when insufficient coke is present, consist-
ing of carbon, silicon, and oxygen, while on p. 96 the statement is made that
amorphous carborundum contains carbon, silicon, and oxygen.
PRODUCTS OF THE RESISTANCE AND ARC FURNACE 219
fire sand, or siloxicon. The latter name is due to Acheson,
who took out a patent for its production in 1903. 6
In the manufacture of siloxicon it is important not to have
sufficient carbon in the charge to reduce the silica completely,
and to keep the temperature constant within certain narrow
limits. For this purpose the furnace is built with more than
one core, thus making the distribution of temperature more
even. The charge, consisting of one third carbon and two
thirds silica, is made up of powdered carbon, powdered silica,
and sawdust, the silica and carbon contents of the sawdust
being taken into account.
The density of siloxicon is 2.7. 7 When heated in an atmos-
phere containing a large amount of oxygen to about 1470 C.,
it is oxidized, giving silica and carbon dioxide, 8 while in the
absence of oxygen at a higher temperature it is converted into
Siloxicon is used to make crucibles and for furnace lining, as
it is not attacked by melted metals or by slags.
The manufacture of silicon is now carried out by the Carbo-
rundum Company according to patents of F. J. Tone. 1
Arc furnaces are used in which two vertical electrodes ex-
tend for a considerable depth into the charge of coke and sand.
The furnace is built of fire brick lined inside with carbon. Each
furnace has a capacity of 910 kilowatts, and the metal is tapped
out at intervals of a few hours in ingots weighing from 600 to
800 pounds. It is made in different grades, varying from 90 to
97 per cent pure. Silicon is used principally in the steel in-
dustry in place of ferrosilicon. The production of silicon in
1908 was 600 long tons, valued at $72,000. 2 Previous to its
Electrochem. and Met. Ind. 1, 287, (1903).
7 FitzGerald, Electrochem. and Met. Ind. 2, 439, (1904).
e Acheson, Electrochem. and Met. Ind. 2, 373, (1904).
1 Electrochem. and Met. Ind. 7, 192, (1909).
2 Min. Ind. 17, 13, (1908).
220 APPLIED ELECTROCHEMISTRY
manufacture by the Carborundum Company the price of silicon
was $4 a pound.
Silicon can also be made in small laboratory furnaces. 3
Graphite was known to the ancients, but up to the time of
Scheele no distinction was made between it and the closely similar
substance molybdenum sulphide, MoSg. 1 Both leave a mark on
paper and were called plumbago on account of the belief that
they contained lead.
In order to define graphite more definitely, Berthelot 2 proposed
that only that variety of carbon be given this name which, on
oxidation with powerful oxidizing agents at low temperatures,
gives graphitic oxide. Graphitic oxide has different properties,
depending on the differences in the graphite from which it is
made, but all varieties are insoluble and deflagrate on heating.
Amorphous carbon, when oxidized with a mixture of potassium
chlorate and fuming nitric acid, the oxidizing agent used by
Berthelot, is changed to a soluble substance, and diamond is not
affected. This is a method of separating the three different
kinds of carbon.
The artificial production of graphite by dissolving carbon in
cast iron and allowing to cool slowly was first observed by
Scheele in 1778. 1 It has since been made by Moissan by dis-
solving in iron, as well as in a number of other metals, and by
heating pure sugar carbon in the electric arc. 3 Diamond also
may be changed to graphite by heating in the electric arc.
Despretz, 4 in his work on carbon, produced graphite by heating
carbon in an electric furnace. These observations do not agree
with those of Acheson, who early in his experience in the manu-
facture of carborundum noticed that graphite occasionally formed
8 Tucker, Met. and Chem. Eng. 8, 19, (1910).
1 Roscoe and Schorlemmer, Treatise on Chemistry, 3d ed. Vol. 1, p. 730.
2 Ann. de Chim. et de Phys. (4) 19, 393, (1870).
3 Moissan, The Electric Furnace, p. 61. See also FitzGerald, Kunstlicher
Graphite, Vol. 15 of the Engelhardt Monographien.
* C. R. 28, 755 ; 281, 48 and 709, (1849).
PRODUCTS OF THE RESISTANCE AND ARC FURNACE 221
next to the core, 5 and that when coke from bituminous coal was
used for the core quite a large amount of it was converted into
graphite, whereas when the purer petroleum coke was used very
little was so changed. The greater the amount of impurity in
the coke, the larger was the amount of graphite produced. These
facts led Acheson to the theory that graphite is not produced
by simply heating carbon, but that a carbide must first be pro-
duced and then decomposed by a higher temperature, volatilizing
the metallic element and leaving the carbon in the form of
graphite. The effect of the impurities is catalytic, since the
amount of graphite formed was always too great to be accounted
for by the simple decomposition of the quantity of carbide cor-
responding to the impurity present. If only a small amount of
impurity is present, it is lost by volatilization before all the carbon
can be graph itized. Acheson also found that the production of
graphite was greatly increased by adding a considerable quantity
of any substance that could form a carbide, such as silica, alumi-
num oxide, lime, or iron oxide. 6 At first the charge was made up
with enough impurity to change all the carbon to carbide at
once. For example, a charge would consist of 50 per cent coke,
with sand, salt, and sawdust. Carborundum was then formed
and by heating to a higher temperature the carborundum is
decomposed, leaving graphite. It was found, however, that so
much carbide-forming element was not necessary and that such
substances as anthracite coal that had impurities evenly dis-
tributed through them could be converted into very pure graph-
ite. 7 This is at present one of the principal kinds of carbon used
in this industry.
Intimate mixture of carbon and the impurity is not necessary,
as the carbide-forming element can be vaporized and caused to
penetrate the entire charge, thereby converting it to graphite. 8
Petroleum coke is one form of carbon used in this process.
Lumps of the coke are imbedded in powder formed from the
same material and 5 per cent of iron oxide is sprinkled in. The
iron oxide is reduced, iron is formed at the bottom of the furnace,
5 Journ. Franklin lust. 147, 476, (1899). 7 U. S. Pat. 645,285, (1899).
6 U. S. Pat. 568,323, (1893). U. S. Pat. 711,011, (1900).
and as the temperature is raised volatilizes and penetrates the
whole charge. A very soft quality of graphite is obtained when
the carbide-forming material is more than 20 per cent by weight
of the charge, but less than the amount necessary to change all
the carbon to carbide at once. 9
The furnaces for graphitizing carbon in bulk have a central
core similar to the carborundum furnace. 10
FIG. 89. Section of graphite furnace for rectangular electrodes
FIG. 90. Section of graphite furnace for circular electrodes
In making graphite into electrodes, crucibles, or other finished
products, a mixture of 97 per cent carbon and 3 per cent iron
9 U. S. Pat. 836,355, (1906). 10 Richards, Electrochein. Ind. 1, 54, (1902).
PRODUCTS OF THE RESISTANCE AND ARC FURNACE 223
oxide 11 is mixed with a binding material consisting of water and
a little molasses, and is molded into the desired form. The
molded objects are then dried and placed in the furnace, where
they are changed to graphite without altering their shape. Fig-
ures 89 and 90 show the methods of arranging rectangular and
FIG. 91. Electric furnace in which graphite is made artificially by the
International Acheson Graphite Company, Niagara Falls
circular electrodes respectively. The base of the furnace consists
of bricks, covered with a refractory material, h. The end walls,
6, are of brick and hold the carbon electrodes, c. The bottom
of the furnace is covered with a layer of granulated coke about
5 centimeters thick, on which the electrodes are placed in piles
at right angles to the axis of the furnace, separated from each
other by about one fifth the width of the electrodes. This space
is then filled .with granulated coke, g, arid the furnace is covered
with a mixture of coke and sand, i. Figure 91 is from a photo-
graph of the furnace now used for graphitizing carbon in all
u U. S. Pat. 617,029, (1898).
The following data are given by FitzGerald : 12
Distance between terminals 360 inches
Length of space filled by electrodes 302 inches
Length of space filled by granular carbon .... 58 inches
Length of electrodes under treatment 24 inches
Width of electrodes under treatment 5 inches
Height of pile of electrodes 17 inches
Initial voltage 210 volts
Initial amperage 1400 amperes
Final voltage 80 volts
Final amperage 9000 amperes
In 1902 the plant of the International Acheson Graphite
Company consisted of ten furnaces and 1000 available horse
power. In 1909 the plant was increased to 22 furnaces and 4000
horse power. 13
The yearly production of manufactured graphite is given in
Table 26. 14 "
The Production of Graphite
VALUE IN DOLLARS
1900 . .
1902 . . .
1909 . .
12 Electrochem. and Met. Ind. 3, 417, (1905).
1 3 Electrochem. and Met. Ind. 7, 187, (1909).
i* Min. Ind. 18, 384, (1909). The figures in the table are rounded off.
PRODUCTS OF THE RESISTANCE AND ARC FURNACE 225
6. CARBON BISULPHIDE
Great improvement has been made in the manufacture of
carbon bisulphide by using an electric furnace in place of the
small clay or iron retorts
which have to be heated ex-
ternally. In the old process,
only a small fraction of the
heat applied to the outside of
the retort penetrated to the
mixture of carbon and sulphur
inside, and the process was
so disagreeable on account of
small leaks and the high tem-
peratures of the retort room
that some manufacturers gave
it up altogether. E. R. Tay-
lor, 1 however, has succeeded in
overcoming these difficulties
entirely by the use of the fur-
nace shown in cross section in
Figure 92, patented in 1899 2
and in operation at Perm Yan,
New York. This furnace is
12.5 meters high and the diam-
eter at the base 4.87 meters. 3
At a height of 3.68 meters the
diameter is reduced to 2.5 me-
ters for a distance of 4.87 me-
ters, where it narrows down to
the top for the remaining
length. The electrodes are at
the base and are four in num-
ber, arranged 90 degrees apart. FIG. 92. Taylor's electric furnace for
Opposite electrodes are Con- making carbon bisulphide
1 E. R. Taylor, Trans. Am. Electrochem. Soc. 1, 115, (1902) and 2, 185, (1902)
2 U. S. Pat. 688,364, filed 1899, renewed 1901.
3 Haber, f. Elektroch. 9, 399, (1903).
226 APPLIED ELECTROCHEMISTRY
nected to the same terminal of the alternating current machine.
Wear on the electrodes is reduced to practically nothing by
covering them with conducting carbon, which acts as the re-
sistor. Charcoal is fed in at the top and sulphur through the
annular spaces in the walls, thus preventing loss of heat. The
sulphur is melted by the heat which would otherwise be lost
through the walls, and flows down on to the electrodes, where
it is heated to a temperature at which it combines with carbon.
The carbon bisulphide vaporizes, passes off through the top of
the furnace, and is condensed in cooling coils. The furnace is
so tight that no odor is noticeable, and its operation is contin-
uous. The production in 1903 was 3175 kilograms per day, with
a consumption of 220 horse power 3 and the furnace had been in
operation for two and a half years with only one interruption
for the purpose of cleaning out.
Phosphorus is another product the manufacture of which
has been improved by the use of heat derived from electricity.
The older method consists in treating calcium phosphate with
sulphuric acid, which changes the triphosphate to monophos-
Ca 3 (P0 4 ) 2 + 2 H 2 S0 4 = 2 CaSO 4 + CaH 4 (PO 4 ) 2 .
The monophosphate is then mixed with carbon and dried, by
which it is changed to metaphosphate :
CaH 4 (P0 4 ) 2 = Ca(P0 8 ) 2 + 2 H 2 O.
The metaphosphate is then heated in small retorts in which
the following reaction takes place :
3 Ca(PO 3 ) 2 + 10 C = Ca 3 (PO 4 ) 2 + 10 CO + 4 P.
This process is imperfect in that a portion of the phosphorus
is changed in the last operation to the product with which the
operation is begun. Wohler proposed the use of silica and
carbon, by which all the phosphorus would be recovered, as
shown by the following reaction :
Ca 3 (PO 4 ) 2 + 3 SiO 2 + 5 C = 3 CaSiO 3 + 5 CO + 2 P,
PRODUCTS OF THE RESISTANCE AND ARC FURNACE 227
but it was never successful till the introduction of the electric
furnace, on account of the difficulty of obtaining the necessary
temperature and of finding vessels to withstand it. 1 In 1889
the use of electric furnaces for the manufacture of phosphorus
was patented by J. B. Readman. 2 The process does not seem
to have been immedi-
ately employed on a
large scale, however.
In 189T the firm of
Allbright and Wilson
built works at Niagara
Falls, using 300 horse
power, for making
phosphorus in the
fnr The Roadman-Parker electric furnace for produc-
The furnaces FlG . 93. Vertical FIG. 94. Horizontal
are illustrated in Fig- section section
ures 93 and 94. Each produces 170 pounds a day.
Over half the world's production of phosphorus is now
made in electric furnaces. 4
Fused aluminum oxide, chemically identical with corundum,
has received the trade name of Alundum. The process for
making this abrasive in the electric furnace was patented in
1900 by C. B. Jacobs. 6 His furnace was rectangular in shape,
made of sheet iron and brick, and was lined inside with car-
bon. An arc was formed between four pairs of electrodes near
the movable bottom of the furnace. As the aluminum oxide
fused and covered the bottom of the furnace, it was gradually
lowered, thereby making a layer of fused aluminum oxide
which cooled slowly. This process gives the abrasive a hard-
ness greater than corundum.
i Min. Ind. 14, 494, (1905). Min. Ind. 6, 637, (1897), 7, 557, (1898).
2U. S. Pat. 147,943, (1889). *Min. Ind. 9, 768, (1900).
6 U. S. Pat. 659,926, (1900).
The Norton Emery Wheel Company of Worcester are the
sole manufacturers of alundum. Their factory is at Niagara
Falls. Bauxite, the raw material, is dehydrated before feeding
into the furnaces. The yearly production is given in Table 27. 6
Production of Alundum
VALUE IN DOLLARS
4 020 000
3 612 000
With the exception of silicon and oxygen, aluminum is the
most widely distributed element in nature, 1 occurring princi-
pally as silicates in clays. Only a limited number of its com-
pounds can be used for extracting aluminum, however, chief
among which is bauxite, A1O 3 H 3 . The name aluminum is
derived from alumen, a term applied by the Romans to all
bodies of astringent taste.
The attempts to isolate aluminum date from 1807, when Davy
was unsuccessful in applying to this problem the method em-
ployed in isolating the alkali metals. Oersted seems to have
made aluminum in 1824 by heating the chloride with potassium
amalgam. Wohler in 1827 obtained aluminum by decompos-
ing the anhydrous chloride with potassium, and in 1864 Bunsen
and Deville obtained it independently by the electrolysis of
fused aluminum chloride. Previous to the production by the
method of electrolysis now used, the halide salts were the
source of the metal and were reduced by metallic sodium.
Alumina can be reduced by carbon to metallic aluminum by
6Min. Ind. 18,25, (1909).
1 Thorpe, Die. of Chem. 1, 63, (1890).
PRODUCTS OF THE RESISTANCE AND ARC FURNACE 229
heating to a temperature above 2100 C., 2 but it is always mixed
with aluminum carbide, from which it can be removed by
remelting, and obtained in a compact form. This is evidently
not a method of making aluminum that could be satisfactorily
carried out commercially. If, however, a metal such as copper
is added to the mixture, the aluminum can be obtained as an
alloy with this other metal. This process was patented in
1884 by the Cowles brothers. 3 The cheap production of pure
aluminum, however, was made possible by the discovery of
C. M. Hall 4 that alumina, dissolved in a molten mixture of
aluminum fluoride and the fluoride of another metal, forms an
electrolyte which may be decomposed by an electric current,
liberating aluminum at the cathode and oxygen at the anode.
Hall's original patent specifies a mixture of 169 parts by weight
of aluminum fluoride and 116 parts of potassium fluoride,
corresponding to the formula K 2 A1 2 F 8 , and states that this may
be made more fusible by replacing part of the potassium
fluoride by lithium fluoride, or by simply adding the latter to
the above mixture. Another receipt is 84 parts of sodium
fluoride to 169 of aluminum fluoride, which may be made by
adding aluminum fluoride to cryolite, a mineral of the com-
position A1F 8 3 NaF. He placed the carbon-lined crucible in a
furnace, melted the mixture, added alumina, and electrolyzed
with an anode of copper or carbon. Copper is said to be
covered with an oxide which protects it from further action.
Subsequent patents show that these mixtures worked well
at first, but became less efficient after being electrolyzed some
time. A dark substance formed which interfered with the
electrolytic action, increased the resistance, and necessitated a
change of the bath. This Hall attempted to overcome by
using a bath of calcium and aluminum fluoride of the com-
position 2 A1F 3 ' CaF 2 . 6 This increases the density to such an
extent that the aluminum floats to the surface. It evidently
2 Hutton and Petavel, Phil. Trans. 207, 421, (1907) ; Askenasy and Lebedeff,
Z. f. Elektroch. 16, 565, (1910).
8 U. S. Pat. 319,795, (1884). Also Proc. Soc. of Arts, 1885-1886, p. 74.
* U. S. Pat. 400,664 and 400,766, filed 1886.
U. S. Pat. 400,664, filed 1888.
230 APPLIED ELECTROCHEMISTRY
was not satisfactory, for subsequently a bath made up of 234
parts calcium fluoride, 421 parts cryolite, 845 parts aluminum
fluoride, and 3 to 4 per cent calcium chloride was patented. 6
It was claimed that the chloride prevented the clogging of the
bath even when in continuous operation. It is evident the
dark color must have come from carbon, as no clogging
occurred with any of the baths when a metal was used as
cathode. 7 In this case, of course, an alloy of aluminum would
As carried out on a large scale, the crucibles were never
heated externally, but simply by the passage of the current it-
self. This double use of the current to keep the bath melted
and to electrolyze at the same time was patented by Charles S.
Bradley. 8 In describing his process, cryolite is considered the
electrolyte. The two patents of Hall and Bradley taken to-
gether represent the process as actually carried out.
In 1887 Paul Heroult patented a very similar process for
producing aluminum alloys. 9 This process consisted in fusing
pure alumina and keeping it in the fused state by the current,
which at the same time decomposes the oxide electrolytically.
The cathode is a melted metal, with which the aluminum is to
be alloyed, and the anode is carbon. Serious objections were
found to using any flux. Among those tried and discarded was
cryolite. The patent states that satisfactory results were ob-
tained with a carbon crucible 20 centimeters in depth and 14
centimeters in diameter at the top, a carbon anode 5 centimeters
in diameter, and a current of 400 amperes at from 20 to 25 volts.
This voltage is four or five times that specified by Hall. Brad-
ley's patent for the simultaneous use of the current for electrol-
ysis and heating was therefore earlier than Heroult's, and as it
is stated in Heroult's patent that he had failed to get good re-
sults when any flux was mixed with the aluminum oxide, there
is no question of priority over Hall's patents. It does not seem,
therefore, that the statement often met with, that the processes
s U. S. Pat. 400,666, filed 1888. 7 U. S. Pat. 400,667, filed 1888.
8 U. S. Pat. 464,933, filed 1883, granted 1891.
U. S. Pat. 387,876, filed December, 1887.
PRODUCTS OF THE RESISTANCE AND ARC FURNACE 231
of Hall and Heroult are identical, is borne out by the patents. 10
The Hall patents for the composition of the bath expired in
1905 and the Bradley patents in 1909. u
The only producer of aluminum in this country is the Alumi-
num Company of America, previous to 1907 known as the Pitts-
burg Reduction Company. 12 This company controls three plants,
situated at Niagara Falls, Massena, New York, and Shawinegan
Falls, Canada. These plants were enlarged in capacity in 1907
to 40,000 horse power, 20,000 horse power, and 15,000 horse
power respectively. 13 The six European companies producing
aluminum show a maximum consumption of 97,500 horse power. 13
The furnaces used by the American company consist of cast
iron troughs lined with carbon. 14 The anode is composed of 48
carbon rods 3 inches in diameter and 15 inches long, manufac-
tured by the aluminum company for its own use. 12 Each fur-
nace takes about 10,000 amperes at about 5.5 volts. The yield
is 1.75 pounds of aluminum per horse power day. 1 * The metal
sinks to the bottom and is drawn off, while alumina is thrown
in as it is used up. The temperature of the bath may be in-
ferred from the following melting points of mixtures of cryolite
and alumina. 16
Melting Points of Mixtures of Cryolite and Alumina
M. P., DEGREES
M. P., DEGREES
10 See for example Pring, Some Electrochemical Centres, p. 26 (1908).
" Min. Ind. 17, 23, (1908). 18 Min. Ind. 6, 11, 15, (1907).
12 Min. Ind. 15, 11, (1906). u Min. Ind. 14, 15, (1905).
is Pyne, Trans. Am. Electrochem. Soc. 10, 163, (1906).
The production of aluminum in the United States and Canada
is given in Table 29. 16
Production of Aluminum in the United States and Canada
VALUE PER POUND
1903 . . .
13 000 000
The total production of the world for 1909 is estimated at
24,200 metric tons, or 53,300,000 pounds. The cost of manu-
facture excluding amortization is said to be about 15 cents a
On reading a description of the different expedients patented
by Hall to prevent the baths from clogging, becoming discolored,
and ceasing to operate properly, it is not surprising that diffi-
culties are encountered on attempting to use the reduction of
aluminum as a laboratory experiment. Haber and Geipert 17
succeeded in a few runs, though in the last run they met with
irregularities. The immediate difficulty that stops an experi-
ment on a small scale is a polarization at the anode, due to a
thin film of gas, 18 which reduces the current to such a point that
the bath freezes up. If a higher voltage is applied it heats the
is Min. Ind. 18, 17, (1909).
IT Z. f. Elektroch., 8, 1, and 26, (1902).
i 8 Thompson, Electrochem. and Met. Ind. 7, 19, (1909). Also Neumann and
Olsen, Met. and Chem. Eng. 8, 185, (1910).
PKODUCTS OF THE RESISTANCE AND ARC FURNACE 233
bath too much locally and burns up the aluminum. By the
use of an anode with a large area this can be prevented to a
certain extent. 18
One of the principal uses for aluminum is in the iron and
steel industry as a reducing agent. 19 As is well known, it has
replaced copper, tin, and brass to a great extent in the manu-
facture of a large number of objects in which lightness is
10. SODIUM AND POTASSIUM
Sodium and potassium were first isolated by Davy l by electro-
lyzing the corresponding fused hydrates. In this process
sodium is liberated at the cathode while the negatively charged
hydroxyl ion is liberated at the anode. Two of these ions when
discharged react together according to the reaction:
2 OH = H 2 O + O.
A certain amount of metallic sodium dissolves in the hy irate,
diffuses to the anode, and coming in contact with the water
reacts to form hydrate with the liberation of hydrogen. 2 It is
therefore possible to have both hydrogen and oxygen evolved
at the anode, resulting in explosions. At the same time sodium
peroxide (Na 2 O 2 ) is formed. The water formed at the anode is
not driven off by the temperature of the bath ; on the contrary
it has been found that very moist air is dried to a certain extent
in passing through the melted hydrate. 2
The apparatus nearly universally used for the production of
sodium and potassium is due to Hamilton Young Castner 3 and is
shown in Figure 95. It consists in a cast-iron box with an iron
cathode, H, insulated from the box and held in an iron pipe
fastened into the bottom of the cell. The space between the
pipe and electrode is filled with melted hydrate which is allowed
to solidify before the electrolysis is begun. Surrounding the
19 For a detailed account of the various purposes to which aluminum is applied,
see A. E. Hunt, Journ. Franklin Inst., Vol. 144, (1897).
1 Phil. Trans., 1808, pp. 5 and 21.
2 Lorenz, Elektrolyse Geschmolzener Salze, I, 25, (1905).
8 U. S. Pat. 452,030, filed 1890.
cathode is a fine iron gauze diaphragm, M, outside of which is
the iron anode, F. The metal is liberated on the cathode and
floats to the surface of the hydrate, where it collects in an iron
cylinder forming a continuation of the diaphragm. It is re-
moved by an iron spoon with fine perforations, which allow the
hydrate to drain off, but which holds the metal. The hydrate
is added as it is used up, and the process is continuous. An
important point is to maintain the temperature as low as pos-
sible, not over 20 above the melting point of the hydrate. The
FIG. 95. Castner's cell for producing sodium and potassium
higher the temperature the less the yield in metal, due of course
to its greater solubility in the melted hydrate. As the temper-
ature increases, the yield becomes less, until it finally reaches
zero. At best the current efficiency is said to be only about 45
per cent. 4 In the patent gas heating is provided, though it is
stated that the current can be so regulated as to keep the proper
temperature without external heating.
There are other processes very similar to that of Castner,
some of which are in use, 6 which will be omitted as presenting
4 Ashcroft, Trans. Am. Electrochem. Soc. 9, 123, (1906).
6 See H. Becker, Die Elektrometallurgie der Alkalimetalle, p. 52, (1903).
PRODUCTS OF THE RESISTANCE AND ARC FURNACE 235
no new principles; but the principle of the following process,
due to Ashcroft, 4 will be described because of its novelty and
in spite of the fact that it does not seem as yet to have been
carried out on a commercial scale. Melted sodium chloride is
electrolyzed with a lead cathode. The lead sodium alloy formed
is let into another cell containing melted sodium hydrate. Here
the lead alloy acts as the anode and forms sodium hydrate with
the hydroxyl ions liberated on its surface, thus avoiding the
formation of water and oxygen. At the cathode sodium is lib-
erated and removed. To decompose the chloride 7 volts are
required, and 2 volts for the hydrate when this anode is used.
The voltage is therefore about twice that required in the
Castner cell; but as the current efficiency is about 90 per cent,
or twice that in the Castner process, the yield per unit of
power is the same in the two cases. The advantages claimed
by Ashcroft are shown in the following table:
Cost of power per pound of sodium . .
1 to 5 cents
1 to 5 cents
Upkeep and standing charges ....
5 to 9 cents
10 to 14 cents
The saving comes in the greater cheapness of the raw material,
and there would be a further saving in the value of the chlorine
The world's production of sodium in 1907 is estimated at from
3500 to 5000 tons. 6 In the United States there are two com-
panies producing about 2000 tons a year. The Electrochem-
ical Company at Niagara Falls uses the Castner process, while
the Virginia Electrolytic Company at Holcomb Rock, Virginia,
is said to employ a process in which fused sodium chloride is
e Min. Ind. 17, 772, (1908).
236 APPLIED ELECTROCHEMISTRY
A large part of the sodium made is consumed in the manu-
facture of sodium cyanide and sodium peroxide. The process
for cyanide 7 consists in passing ammonia over the metal heated
in an iron retort to 300 to 400 C., forming sodamide :
2 Na + 2 NH 3 = 2 NaNH 2 + H 2 .
This is then treated with charcoal previously heated to redness,
giving the cyanide
NaNH 2 + C = NaCN + H 2 .
A recent purpose to which the metal has been put is the dry-
ing of transformer oils. Ashcrof t 4 believes a reduction in the
price may increase its uses materially, such as making primary
cells, obtaining hydrogen by the decomposition of water, and
even for transmitting electric power. The specific conductiv-
ity is only about one third that of copper, 8 but if equal weights
of metal are considered between two given points, the conduc-
tivity would be three times that of copper, as the density of
copper is about nine times that of sodium. Some experiments
have actually been carried out in power transmission with the
sodium protected in iron pipes. 9
Calcium was first isolated by Davy in 1808, by combining
the methods previously used by him with those of Berzelius
and Pontin. 1 Lime was mixed with red oxide of mercury,
slightly moistened and placed on a piece of platinum. A glob-
ule of mercury in a cavity at the top acted as negative elec-
trode, giving on electrolysis an amalgam of calcium, from which
the mercury was distilled.
Bunsen 2 obtained calcium in very small quantities contain-
ing a little mercury by electrolyzing with a high current
density a boiling concentrated solution of calcium chloride
7 Roscoe and Schorlemmer, 2, 276, (1907).
8 Landolt-Bornstein Tables, 3d ed.
Belts, Min. Ind. 15, 688, (1906) and El. World, 48, 914, (1906).
1 Alembic Club Reprints, No. 6, p. 48, Ostwald Klassiker, No. 45.
2 Fogg. Ann. 91, 623, (1854), in an article on the preparation of chromium.
PRODUCTS OF THE RESISTANCE AND ARC FURNACE 237
acidified with hydrochloric acid. The cathode was amalga-
mated platinum wire. Rathenau 3 was first to obtain calcium
in a compact form in fairly large quantities by a rather original
method. The bath
consists of calcium
chloride very little
above its melting
point. An iron
rod is used as cath-
ode, which just
touches the surface
of the bath. As
the melting point
of calcium is a little
higher than that of C
the bath, it solidi-
fies on depositing
and adheres to the
rod, which is grad-
ually raised, thus
drawing out a stick
of calcium with a
certain amount of
to it. The melt-
ing point of the
electrolyte may be
lowered by adding FIG. 96. Cell of Seward and von Kiigelgen for the pro-
calcium fluoride. duction of calcium
The anode may be a carbon crucible in which the salt is contained, 4
though Rathenau does not specify his arrangement. The ex-
perience of the author has been that this is a much better plan
than that adopted by P. Wohler, 5 where the salt is held in an
iron vessel and a carbon anode dips into the bath. Due to the
8 Z. f. Elektroch. 10, 608, (1904).
* J. H. Goodwin, Proc. Am. Phil. Soc. 43, 381, (1904).
6 Z. f. Elektroch. 11, 612, (1905).
238 APPLIED ELECTROCHEMISTRY
high anode current density in this case, the gas is more likely
to stop the current by polarization. The heat due to the cur-
rent is sufficient to keep the salt melted.
Calcium is made in this country only by the Virginia Elec-
trolytic Company at Holcomb Rock, Virginia. 6 The process
is supposed to consist 7 in electrolyziiig melted calcium chloride
in a cell patented by Seward and von Kiigelgen, 8 shown in
Figure 96. This cell consists of a circular iron box, J., through
the bottom of which projects a conical iron cathode, B, insulated
from the box by insulating material, aa. The anode, (7, is a car-
bon lining also insulated from the iron box. Above the cathode
and concentric with it is a water-cooled collecting ring, E, which
separates the metal rising to the surface from the chlorine.
The metal accumulates till the ring is full. The top layer is
solid, due to the cooling of the air, and the bottom is soft or
melted. The solid part is fastened to a hook, F, and gradually
The production of calcium by the Virginia Electrolytic Com-
pany in 1907 was 350 pounds, valued at $613, and about the
same amount was produced in 1908. 6
6 Min. Ind. 17, 99, (1908).
'Min. Ind. 16, 131, (1907).
U. S. Pat. 880,760.
THE ELECTROMETALLURGY OF IRON AND STEEL
1. GENERAL DISCUSSION
BEFORE giving an account of the application of electric heat-
ing to the iron and steel industry, a short sketch of the older
methods of winning and refining iron will not be out of place.
The extraction of iron from its ores, consisting principally of
oxides of iron mixed with clay, silica, and other impurities, is
accomplished by reducing the ore with some form of carbon, usu-
ally coke. This operation is carried out in a blast furnace, a cir-
cular brick structure lined with silicious brick, and varying in
size from 48 feet to 106 feet in height, and from 8 feet to 15
feet in diameter at the base. Figure 97 shows the elevation of a
blast furnace. It consists of three principal parts : (1) the cru-
cible or hearth at the base, cylindrical in shape, (2) the bosh
directly above, which gradually widens, and (3) the stack, from
which point the furnace contracts for the rest of its height.
The furnace is filled with alternate layers of ore, coke, and flux,
the latter usually consisting of calcium carbonate. The object
of the flux is to form a fusible slag with the constituents of the
ore which are not reduced by the carbon, such as silica and
alumina. The heat necessary to raise the charge to a temper-
ature high enough for reduction is produced by the combustion
of the coke in the charge, by means of air forced in through the
tuyeres, F, projecting through the wall of the furnace just below
the bosh. The carbon therefore serves the double purpose of
furnishing the heat and of reducing the ore.
The highest temperature of the furnace is near the tuyeres
and a few feet above them ; in this region the slag and iron
melt and drop into the crucible, where they separate, the slag
floating on the iron. These are drawn off from time to time
through the tap holes Or and H, and fresh material is fed into
the top of the furnace by mechanical means. The iron thus
FIG. 97. Elevation of blast furnace
produced is known as pig iron, and contains from three to four
per cent of carbon, as much as four per cent of silicon, and one
per cent of manganese, and a few hundredths of one per cent of
sulphur and phosphorus. Only about 23 per cent of the pig
iron made in this country is used without subsequent purifica-
tion. 1 Purification or refining of iron is accomplished by oxi-
dizing the impurities and causing them to form a slag, which
floats on the iron.
1 Stoughton, The Metallurgy of Iron and Steel, p. 52.
THE ELECTROMETALLURGY OF IRON AND STEEL 241
One method of refining consists in blowing air through the
liquid metal in a Bessemer converter. The lining of the con-
verter may be either basic, consisting of calcined dolomite (cal-
cium and magnesium oxides), or acid, consisting of silica. The
Bessemer method is very rapid, silicon and manganese oxidizing
in about four minutes from the time when the air is first blown
in. The carbon then begins to oxidize to carbon monoxide,
which boils up through the metal and comes out of the con-
verter in a long flame. In about six minutes from the time the
carbon begins to oxidize, it is reduced to approximately 0.04
per cent, and the operation is then stopped. The temperature
is higher at the end of the process than at the start, due to
the heat of oxidation of the impurities. A calculated amount
of carbon is then added, also 1.5 per cent of manganese to
remove the oxygen, and 0.2 per cent of silicon to remove the
other gases. The steel is then cast into molds.
The second method of refining is known as the open hearth or
Siemens-Martin process. This consists in melting the pig iron
in a large reverberatory furnace, whose lining may be either
basic or acid. The oxidation of the impurities is brought about
by the excess of oxygen in the furnace gases over that neces-
sary to burn the gases. A much longer time is required for
purification by the open hearth than by the Bessemer process.
In the basic open hearth process enough lime is added to form
a very basic slag, which, unlike an acid slag, will dissolve phos-
phorus. The lining must also be basic to prevent its being
eaten away by the basic slag.
The third method of purification is known as the puddling
process, in which the iron is melted on the hearth of a rever-
beratory furnace lined with oxides of iron. The pig iron is
charged by hand through the doors of the furnace and is melted
as quickly as possible. During melting, silicon and manganese
go into the slag, as well as some of the oxide of the lining.
Iron oxide is then added in order to make a very basic slag ;
the charge is thoroughly mixed, and the temperature is lowered
to the point where the slag begins to oxidize the phosphorus
and sulphur before the carbon. After the removal of these
242 APPLIED ELECTROCHEMISTRY
impurities, the carbon begins to oxidize and comes off as carbon
monoxide, which burns on coming in contact with the air.
During this time the puddler stirs the charge vigorously with a
long iron rabble, an instrument shaped like a hoe. As the iron
becomes pure, its melting point rises and it begins to solidify,
since the temperature of the furnace is below the melting point
of pure iron. The iron is finally removed in the form of a ball
dripping with slag, and is put through a squeezer to remove the
slag as much as possible. This product is known as wrought
iron. It is converted into steel by two methods, (1) the ce-
mentation, and (2) the crucible process. In the cementation
process the wrought iron is carburized by heating, without
melting, in contact with carbon. The carbon slowly penetrates
the iron and changes it to steel. In the crucible process the
wrought iron is cut up into small pieces and is melted in covered
crucibles with the desired amount of carbon or other element
that is to be alloyed with it. When the process is finished the
steel is cast into molds. By thus remelting the iron, the slag
is removed and the required amounts of carbon, silicon, and
manganese are added.
2. THE ELECTROTHERMIC REDUCTION OF IRON ORES
The conditions under which electric heating can economically
be substituted for the heat of combustion of coke in the reduc-
tion of iron ores are purely local. In places where iron ore
can be obtained cheaply, where metallurgical coke is expensive,
where water power is cheap, and where iron would have to be
hauled from a great distance to supply the local demand, it
may be possible to produce iron by electric heating at a price
low enough to compete with that brought from a distance.
These conditions exist in Canada, Sweden, and California. 1
The first attempt to apply electric heating to the metallurgy
of iron was made in 1853 by Pinchon, 2 and in 1862 Monkton
took a patent in England for the reduction of ores by the
1 Eugene Haanel, Trans. Am. Electrochem. Soc. 15, 25, (1909) l and P. McN.
Bennie, ibid. p. 35.
2 B. Neumann, Electrometallurgie des Eisens, p. 3, (1907).
THE ELECTROMETALLURGY OF IRON AND STEEL 243
FIG. 98. Stassano's first furnace at Rome
electric current. Sir Wil-
liam Siemens again called
attention to this subject
in a lecture before the
Society of Telegraph En-
gineers in London in 1880. 3
The first, however, to show
by experiments on a large
scale that iron can be re-
duced commercially by
electric heating was the
Italian army officer, Major
Stassano. 4 Patents were
taken out by him in the year 1898 in different countries, con-
sequently this date
marks the beginning
of the actual appli-
cation of electricity
to the metallurgy of
iron. The contrac-
tion of the carbide
industry in 1899 to
1900, due to over-
idle a number of
France, for which
some new application
of electric power was
needed, also hastened
the introduction of
electric heating in the
iron industry. 6
FIG. 99. Horizontal section of Stassano's electric
furnace at Darfo
Elektrotech. Z. 1, 325, (1880).
4 Askenasy, Technische Elektrochemie, 94, (1910).
6 J. B. C. Kershaw, Electrometallurgy, p. 175, (1908).
inary experiments on the reduction of iron ore were carried
out at Rome in 1898, 6 with the 150 horse power furnace repre-
sented in Figure 98. It is seen to resemble an ordinary blast
furnace. Since there was no combustion of carbon, no reduc-
ing gases were produced ; consequently, in order to bring the
FIG. 100. Vertical section of Stassano's electric furnace at Darfo
carbon and ore in intimate contact, they were powdered, mixed,
and made into briquettes with pitch as a binder. The furnace
6 See an article by Stassano reprinted in Haanel's Keport, p. 178, (1904).
THE ELECTROMETALLURGY OF IRON AND STEEL 245
was first heated without a charge ; an iron grating was then
placed in the furnace 20 centimeters above the arc, and the mix-
ture was charged in from the hopper at the top and was held
up by the grating. The grating eventually melted, and the
ore in contact with it was reduced. In this state the mixture
which lay on the grating became fused and formed an arch,
which supported the charge even when the grating melted
away. As the heat from the arc penetrated the mass above the
arch, iron was reduced and dropped into the crucible below.
In the course of twelve hours the arch increased so in thickness,
due to the slag produced, that it prevented the efficient heat-
ing of the charge above. Consequently this form of furnace
was given up, and one was adopted in which the material was-
introduced below the arc, as is done in refining furnaces. The
final form adopted at Darfo,
in northern Italy, is shown
in Figures 99 and 100.
Movement of the entire
chamber in which the fu-
sion takes place is effected
by rotating about an axis
inclined to the vertical.
The electricity is conducted
to the furnace by sliding
contacts on two metal rings
at the top of the furnace.
This, furnace worked per-
fectly satisfactorily, even
when run for several days.
The most difficult ques-
tions to decide were the re-
lation between the size of the cavity and the energy to be
supplied, and the manner of making the refractory lining. The
carbon electrodes were 1.5 meters long and lasted sixty consec-
utive hours. The furnace was supplied with 1000 amperes at
100 volts, and since the value of the cosine of the phase differ-
ence between electromotive force and current was 0.8, the power
FIG. 101. The Keller electric furnace for
reducing iron ore
246 APPLIED ELECTROCHEMISTRY
consumed was 80 kilowatts. The best yield with this furnace
was one kilogram of soft iron for 3.2 kilowatt hours, and the
iron obtained was always over 99 per cent pure. The ore,
which was from the island of Elba, had the following com-
Fe 2 O 3 93.020 per cent
MnO 0.619 per cent
SiO 2 3.792 per cent
CaO, MgO 0.500 per cent
Sulphur , 0.058 per cent
Phosphorus 0.056 per cent
Moisture 1.720 per cent
According to Stassano, the plant at Darfo was shut down
for reasons not directly connected with the success of the
The Keller furnace for making pig iron is shown in Figure
101. This furnace was seen in operation by the Canadian
Commission at Livet, France, in 1904. It T consists of two
iron castings of square cross section, forming two shafts com-
municating with each other at their lower ends by a lateral
canal. The castings are lined with refractory material. The
base of each shaft is provided with a carbon block, these two
blocks being connected to each other outside the furnace by
copper bars. On starting, before there is metal in the canal,
the current flows from one block to the other through the copper
bar, but when enough metal has been reduced to partially fill
the canal, most of the current flows through the melted metal.
The electrodes are 1.4 meters long and 85 by 85 centimeters in
cross section. The cost of electrodes per metric ton of pig iron
is estimated by Keller at 3.85 francs. The energy absorbed
per metric ton of pig iron in a furnace supplied with 11,000
amperes at 60 volts was 0.390 kilowatt year for the run, and
with a smaller furnace supplied with 7000 amperes at 55 volts
it was 0.186 kilowatt year for the run. 8
Haanel's Report, p. 15, (1904). Haanel's Report, p. 20, (1904).
THE ELECTROMETALLURGY OF IRON AND STEEL 247
Following the tour of inspection by the Canadian Commission,
an investigation was carried out for the Canadian government
in 1906 by Heroult, to see (1) whether magnetite could be eco-
nomically smelted by the electrothermic process ; (2) whether
ores containing sulphur, but not manganese, could be made into
pig iron of marketable composition ; and (3) whether charcoal
could be substituted for coke. The
furnaces were slightly modified as the
investigation proceeded, and the final
form is shown in Figure 102. It
consists of a cylindrical iron casting
| inch thick, bolted to a bottom plate
of cast iron 48 inches in diameter.
The casting was made in two sections
bolted together by angle irons. In
order to make inductance small, the
magnetic circuit was broken by re-
placing a vertical strip of 10 inches
width in the casting by copper. Rods
of iron were cast into the bottom plate
to secure good contact with the car-
bon paste rammed into the lower part
of the furnace. The electrodes, 6
feet long and 16 by 16 inches in cross
section, were manufactured by a pro-
cess of Heroult's and were imported
from Sweden. The pipe k was for the purpose of cooling the
electrode holder by a current of air. The current was between
4000 and 5000 amperes at 36 to 39 volts, and the power factor
was 0.919. The ores used in the experiments below were of
the following composition:
FIG. 102. Heroult experimen-
tal furnace at Sault Ste.
Marie, for reducing iron ore
Composition of Ores investigated by Heroult for the Canadian Government
Fe 2 3
A1 2 3
CO 2 and unde-
Loss on ignition
The consumption of the electrode in these experiments was
8.9 kilograms per metric ton of pig iron produced. The yield
per unit of energy vafried somewhat, but was approximately
0.25 kilowatt year of 365 days per metric ton of pig iron.
The results of these experiments were :
1. Canadian ores, chiefly magnetites, can be as economically
smelted as hematites by the electrothermic process.
2. Ores of high sulphur content can be made into pig iron
containing only a few thousandths of one per cent of
3. The silicon content can be varied as required for the class
of pig iron to be produced.
THE ELECTROMETALLURGY OF IRON AND STEEL 249
4. Charcoal which can be cheaply produced from mill refuse
or wood which could not otherwise be utilized, and peat
coke, can be substituted for coke without being briquetted
with the ore.
5. A ferro-nickel pig can be produced practically free from
sulphur, and of fine quality, from roasted nickeliferous
6. Titaniferous iron ores containing up to five per cent can
be successfully treated by the electrothermic process.
These results demonstrated the feasibility of applying the
electrothermic process to the reduction of iron ores. 9 All that
was necessary to put it
on a commercial basis
was the construction of
a furnace that could be
economically and suc-
cessfully used in prac-
tice. This was under-
taken by three Swedish
engineers, Messrs. Gron-
wall, Lindblad, and Stal-
hane, at Domnarfvet,
Sweden. They concen-
trated their attention on
the construction of a
furnace following the
suggestions contained in
the report of Heroult's
experiments for the
which were, (1) charg-
ing by labor-saving ma-
chinery, (2) collection
and use of carbon monoxide produced by the reduction of the
ore, (3) automatic regulation of electrodes, and (4) a sufficiently
fire BricA 3 Masncsitt
FIG. 103. Electric furnace at Domnarfvet, Swe-
den, for reducing iron ore
9 Haanel, Trans. Ain. Electrochem. Soc. 15, 25, (1909).
250 APPLIED ELECTROCHEMISTRY
high shaft containing the charge to permit the heated carbon
monoxide to produce the maximum reduction of the ore.
Seven furnaces were constructed and tested before arriving at
the one which they considered practical and commercial. This
required over two years and an expenditure of $ 102,000. 1(>
A vertical section of the furnace is shown in Figure 103, from
which the general construction is perfectly obvious. It evi-
dently resembles somewhat Stassano's original furnace, and,
like his, is started as an ordinary blast furnace. 10 The crucible
is 2.25 meters in diameter and 1.5 meters high. The most
important point in the construction is the manner in which
the electrodes are brought into the melting chamber. As seen
from the section, they enter through that portion of the roof of
the crucible that does not come in contact with the charge,
and pass into the charge at the slope formed by the materials
of which it is composed. The electrodes dip into the charge,
but not into the melted iron beneath it. 11 Experiments had
shown that the brickwork lining around the electrodes was al-
ways destroyed if brought in contact with the charge, even
when the electrodes were water cooled. The brickwork com-
posing the lining of the roof of the melting chamber was
cooled by forcing against it, through tuyeres, the compara-
tively cool tunnel-head gases. The heat absorbed by these
gases is given back to the charge above.
A three-phase current is supplied to three electrodes 11 by
22 inches in cross section and 63 inches in length. The water-
cooled stuffing boxes through which the electrodes enter the
melting chamber are provided with devices to prevent the hot
gases under pressure from leaking out around the electrodes.
The results of a short run that was made in the presence of
Dr. Haanel showed (1) that the furnace operated uniformly
and without trouble of any kind for five consecutive days, the
electrodes requiring no adjustment whatever; (2) that the
energy consumption was remarkably uniform ; (3) that a free
10 For the evolution of the furnace, and dimensions, see Met. and Chem,
Eng. 8, 11, (1910).
11 Assar Gronwall, Electrochem. and Met. Ind. 7, 420, (1900).
THE ELECTROMETALLURGY OF IRON AND STEEL 251
space was maintained between the charge and the roof of the
heating chamber ; (4) that the charge did not jam at the lower
contracted neck of the shaft, but moved with regularity into
the melting chamber; and (5) that the lining of the roof of
the melting chamber was effectively cooled by the circulation
Since the short run witnessed by Dr. Haanel, the furnace has
been in continual operation
for 85 days, and met all the
requirements that indicate a
durable furnace. 10 The de-
signers of this furnace have
contracted to erect three large
furnaces for the reduction of
iron ores at Sault Ste. Marie,
Canada, to be in operation by
the middle of 1910. 12 The
first electric smelting plant in
Canada was under construc-
tion at Welland, Ontario, in
1907. 13 It was to consist of
a 3000 horse power furnace
of the latest type brought out
In 1909 an electrothermic
plant for reducing iron ore
was in existence on the Pitt
River at Heroult, Shasta
County, California." From the
section of this 1500 kilowatt
furnace shown in Figure 104, its resemblance to the furnace at
Domnarf vet will be evident. A general view is shown in Fig-
ure 105. Though this furnace is on a commercial scale, in
July, 1910, it was still in the experimental stage, on account
12 Electrochem. and Met. Ind. 7, 535, (1909).
is Haanel's Report, 1907, p. 147.
" D. A. Lyon, Trans. Am. Electrochem. Soc. 15, 39, (1909).
252 APPLIED ELECTROCHEMISTRY
of numerous difficulties that had been encountered. Several
changes have been made and it is expected that the furnace
will be perfected shortly. When this is accomplished, the
Noble Electric Steel Company will build four or five others
of a similar type. 15 Pig iron on the Pacific coast brings $23
to $26 a ton, 16 and the cost from this furnace is expected to
be $15 a ton, which leaves a good margin of profit.
3. THE ELECTROTHERMIC REFINING OF STEEL
While the application of electrothermics to the reduction of
pig iron is scarcely an established commercial industry, the case
is quite the reverse in steel refining, for a large number of fur-
naces for this purpose are in operation in Europe and America.
Even in this case, however, the electric furnace cannot compete
with the Bessemer or with the open-hearth process for making
structural steel. Electric furnace refining is used only to pro-
duce very high-class steel for special purposes, 1 for which it is
far superior to the crucible process, on account of the greater
cheapness and higher quality of the steel produced. 2 The
reason for the better quality of the product is that the atmos-
phere is neutral, and a much higher temperature can be obtained
than by other means, resulting in a more complete removal of
impurities, especially gases. Phosphorus and sulphur disap-
pear nearly completely, and deoxidation is more complete
than that attained by any other means. Another advantage
of electric heating is the reliability and certainty of the
A number of different electric furnaces have been designed
for refining steel, and some of the principal ones will now be
15 private communication from Professor D. A. Lyon, the manager of the
16 Bennie, Trans. Am. Electrochem. Soc. 15, 36, (1909).
1 Haanel's Report, (1904), p. 31; Hibbard, Trans. Am. Electrochem. Soc. 15,
2 Askenasy, Technische Elektrochemie, p. 56, (1910).
3 Askenasy, Technische Elektrochemie, p. 156, (1910).
THE ELECTROMETALLURGY OF IRON AND STEEL 253
FIG. 105. Electric furnace at Heroult, California, for reducing iron ore
254 APPLIED ELECTROCHEMISTRY
The furnace used by Stassano at his works in Turin is
similar to the one he finally adopted for reducing iron ore 4
(Figures 99 and 100). The charge is heated by radiation
from arcs formed between three electrodes placed above the
charge and supplied with a three-phase current. This furnace
also rotates on an axis slightly inclined to the vertical, in order
to mix the charge thoroughly. The lining is magnesite brick. &
Starting with scrap and oxidized turnings, about one kilowatt
hour is required for one kilogram of finished steel in the 250
horse power furnaces used at Turin.
A furnace designed by Charles Albert Keller for steel refin-
ing, which was put into industrial use in 1907, is shown in
Figures 106 and 107. It consists of a crucible with a conduct-
ing bottom for one electrode and a vertical carbon rod for the
other. 6 Since carbon must not be brought in contact with
the melted iron in refining, the bottom must be made conduct-
ing without the use of carbon, and this was accomplished by
Keller as follows : Iron bars from 1 to 1| inches in diameter
are regularly spaced about one inch apart, and are made fast to
a metallic plate at the bottom, covering the entire area on which
the bath will rest. Agglomerated magnesia is then rammed,
while hot, in between the bars. The whole base is surrounded
by a metallic casing for water cooling. Electrical contact is
made by the lower plate to which the bars are fastened. The
furnace is closed by a cover through which the other electrode
passes. After several months' use a hearth constructed in this
manner was found to be in as good condition as on the first
day. The advantage claimed for this arrangement over a
furnace with two vertical electrodes is that the current is more
evenly distributed through the charge, and consequently heats
it more evenly. Of course, the iron bars are melted at their
upper ends where they come in contact with the melted iron to
be refined, but the water cooling prevents them from melting
for more than a few inches of their length.
4 Trans. Am. Electrochem. Soc. 15, 63, (1909).
6 Trans. Am. Electrochem. Soc. 15, 86, (1909).
6 Trans. Am. Electrochem. Soc. 15, 96, (1909).
THE ELECTROMETALLURGY OF IRON AND STEEL 255
I _ 1
/ <* V v ^;oc.a>
FIGS. 106 and 107. Keller conducting hearth furnace
The Heroult steel refining furnace, 7 as shown in Figure 108,
consists of a crucible a with a cover b holding a small chimney
c. As the figure shows, it is arranged for tilting, d are car-
bon electrodes, which may be moved in a vertical or in a hori-
zontal direction. In order to use the furnace for Bessemer-
FIG. 108. The Heroult electric steel furnace
izing, the tuyeres x are provided. The two electrodes do not
quite touch the slag on the surface, so that two arcs are pro-
duced. In passing through the bath, the current, of course,
divides between the slag and the melted iron in proportion to
their conductivities, and as melted iron conducts better than
the slag, a larger proportion would flow through the metal than
through the slag. The poorest kinds of scrap, high in sulphur
and phosphorus, are refined in this furnace. The following
table shows the average refining ability of a 2 J-ton furnace at
La Praz, Savoy :
7 Electrochem. Ind. 1, 64, (1902) ; U. S. Pat. 707,776.
THE ELECTROMETALLURGY OF IRON AND STEEL 257
For a 5-ton furnace, starting with cold scrap, 600 kilowatt
hours are necessary to partially refine one long ton of steel,
and 100 more for the finishing slag. For a 15-ton furnace,
less power would be required.
Figure 109 shows a 15-ton three-phase Heroult furnace at
the South Chicago Works of the Illinois Steel Company.
The steel to be treated is brought directly from the Bessemer
converters, and two refining slags are used in the electric
furnace, the first an oxidizing slag to take out the phosphorus,
and the second, a deoxidizing slag for removing the sulphur
and the gases. 8 Power is supplied to the three electrodes by
three transformers, each of 750 kilowatts capacity. Two
hundred and forty tons of steel are turned out per day in 16
heats. The electrodes, 2 feet in diameter and 10 feet in length,
are the largest ever made in one piece. In cold melting and in
continuous work, the consumption of electrode is from 60 to 65
pounds per ton of steel, but when the metal is charged in the
melted state, the consumption would be reduced to 10 or 15
pounds per ton of steel. This includes the short ends that
cannot be utilized. The linings last from three months to
one year, depending on the care with which the furnace is run;
the roof suffers most, and generally has to be renewed once a
month. The best lining for this furnace is magnesite mixed
with basic slag, with tar for a binder.
The Paul Girod electric furnace 9 is somewhat similar to the
Keller furnace, as seen from Figure 110. One or more elec-
8 Robert Turnbull, Trans. Am. Electrochem. Soc. 15, 139, (1909).
9 Paul Girod, Trans. Am. Electrochem. Soc. 15, 127, (1909).
THE ELECTROMETALLURGY OF IRON AND STEEL 259
trodes of like polarity are suspended above the crucible, while
the electrode of opposite polarity consists of a number of pieces
of soft steel buried in the refractory material of the hearth at
its periphery and water cooled at their lower ends. The
upper ends come in contact with the bath and are melted to a
depth of 2 to 4 inches. About 55 volts are applied to this
furnace. For fusing, refining,
and finishing a charge of cold
scrap in a 2-ton, furnace, about
900 kilowatt hours per metric
ton of steel are required, and in
an 8 to 10 ton furnace, 700 kil-
owatt hours. The electrode con-
sumption is 16 to 18 kilograms
per metric ton of steel produced
in a 2-ton furnace, and 13 to 15
kilograms in an 8 to 10 ton fur-
nace. The short ends are in-
cluded as having been used. The
lining is magnesite or dolomite
brick or paste, and lasts 40 to 50
heats without any repairs what-
An entirely different class of
steel-refining furnaces are those
having the melted metal in the
form of a ring, forming the sec-
ondary of a transformer which is
heated by an induced current
from a primary coil of copper
wire. This type of furnace was
patented in 1887 by Colby in the
United States and by Ferranti
in England. The same principle was applied on a small scale
in 1900 by F. A. Kjellin at Gysinge, Sweden, without knowing
at the time that it had been patented by others. 10 Kjellin,
10 Kjellin, Trans. Am. Electrochem. Soc. 15, 173, (1909).
Fia. 110. The Girod electric steel
however, seems to have been the first to carry this idea out on
a commercial scale. In 1902 a 225 horse power induction fur-
nace was in operation at Gysinge, with an output of 4 metric
tons in 24 hours. This furnace had a magnesite lining in
FIGS. Ill and 112. Elevation and plan of the Kjellin induction furnace
place of silica used in the smaller furnace. A silica lining
lasted only about one week, while the magnesite lasted twelve.
THE ELECTROMETALLURGY OF IRON AND STEEL 261
Figures 111 and 112 show the principle of the Kjellin
furnace. The magnetic circuit C is built up of laminated
sheet iron. D is the primary circuit, consisting of a number
of turns of insulated copper wire or tubing. The ring-shaped
crucible A, for holding the melted metal, is made of refractory
material. This furnace cannot be started by placing cold
scrap in the crucible because of the low induced electromotive
force, but an iron ring must be placed in the crucible and
melted down, or the crucible must be filled with melted metal
taken from another source. The power consumption of the
furnace at Gysinge, starting with cold pig iron and scrap, is
about 800 kilowatt hours per metric ton of product. This
furnace has been found very satisfactory for making the
highest-class steel from pure raw materials.
There is a limit to the current that can be sent through
the liquid metal, and consequently a limit to the temperature
attainable. This is due to a phenomenon first observed by
Paul Bary in 1903, 11 to which the name " pinch effect " was
given by Hering. 12 This phenomenon is as follows : When a
direct or an alternating current passes through a liquid con-
ductor, the conductor tends to contract in cross section, forming-
a depression, and if the current is large enough, the metal in
the trough will separate entirely and break the circuit. This
is due, of course, to the attraction the different elements of
the current exert on each other. It is most likely to happen
at some particular place where the cross section of the ring is
smaller than elsewhere, and if any infusible material falls into
this depression, it may prevent the reunion of the liquid and
cause the charge to .freeze. The largest possible current that
could be passed through liquid iron in a trough 2 inches deep
and 1 inch wide is about 3300 amperes ; in a trough 4 by 2
inches, 9400 amperes ; and in a trough 6 by 3 inches, 17,000
amperes. 13 Larger currents would cause the metal to separate
11 Northrup, Trans. Am. Electrochem. Soc. 15, 303, (1909).
12 Hering, Trans. Am. Electrochem. Soc. 11, 329, (1907) j 15, 255 and 271,
18 Trans. Am. Electrochem. Soc. 15, 269, (1909).
262 APPLIED ELECTROCHEMISTRY
entirely. When a depression is formed, hydrostatic pressure
balances the pressure due to the current, so that this effect
is not so likely to give trouble in a deep channel as in a shallow
one, nor with a heavy metal as with a light one. It has been
found impossible, for instance, to raise aluminum much above
its melting point, in a 60 kilowatt induction furnace on account
of this effect. 14
The Kjellin furnace is not adapted to working with dephos-
phorizing and desulphurizing slags, as the annular ring is not
a convenient shape and offers too small a surface to the attack
of the slag. 15 A combined induction and resistance furnace
was therefore invented by Rodenhauser, known as the Rochling-
Rodenhauser furnace for refining Bessemer steel. A plan and
an elevation of this furnace are shown in Figures 113 and 114.
HH &VQ the two legs of the iron transformer core, surrounded
by the primary windings AA. Surrounding the legs of the
transformer are the two closed circuits of melted metal, forming
together a figure 8, in which currents are induced. BB are
two extra primary coils, from which the current is conducted to
the metallic plates EE. These are covered by an electrically
conducting refractory material, through which the current passes
into the main hearth, D. The result is that the main hearth
can be made with a much larger cross section than the ring in
the original Kjellin furnace, and a good power factor can be
obtained in large furnaces without such a low periodicity as
was necessary with the original induction furnaces. The mag-
nitude of the current from the secondary coils is limited by the
carrying capacity of the refractory material 6r, which would be
destroyed if too heavily loaded. In refining, the furnace is
worked as follows : Fluid steel from the converters is poured
into the furnace, and burnt limestone and mill scale are added
for forming a basic dephosphorizing slag. This is removed,
after the reactions are ended, by tilting the furnace. For mak-
ing rails the phosphorus is reduced sufficiently in one opera-
tion, but for the highest-class steel it has to be repeated.
14 FitzGerald, Trans. Am. Electrochem. Soc. 15, 278, (1909).
16 Kjellin, Trans. Am. Electrochem. Soc. 15, 175, (1909).
THE ELECTROMETALLURGY OF IRON AND STEEL 263
FIGS. 113 and 114. Elevation and plan of the Rochling-Rodenhauser furnace
264 APPLIED ELECTROCHEMISTRY
After removing phosphorus, carbon is added in the pure state
when carbon steel is to be made, and a new basic slag is formed
to remove the sulphur.
Rochling-Rodenhauser furnaces are also built for three-phase
THE FIXATION OP ATMOSPHERIC NITROGEN
NITROGEN, though chemically an inert element, is of great
importance to plant and animal life. It forms 80 per cent by
volume of the atmosphere, but it has been impossible until
recently to get atmospheric nitrogen in a combined state for
use in fertilization or in the chemical industries. This was a
problem of the greatest importance, as the nitrogen removed
from the soil by crops must be replaced either by adding it
in the form of some nitrogen compound or by raising a crop,
such as clover, that assimilates the nitrogen of the air by means
of a certain kind of bacteroid existing on the root of the plant.
Consequently, Chili saltpeter is used in large quantities for fer-
tilization, but as this supply is not expected to last later than
1940, 1 the discovery of some other means of supplying the
demand became imperative.
At present there are three different methods in operation
of combining atmospheric nitrogen. The first method con-
sists in heating calcium carbide in pure dry nitrogen to about
1000 C., whereby nitrogen is absorbed, forming calcium cyana-
mide, according to the reversible reaction :
CaC 2 + NCaCN + C.
The second method consists in oxidizing nitrogen to nitric
oxide in the electric arc and absorbing the oxide in water or in
an alkaline solution, and the third and most recent method is
the direct synthesis of ammonia from its elements.
1 Edstrom, Trans. Am. Electrochem. Soc. 6, 17, (1904).
266 APPLIED ELECTROCHEMISTRY
2. ABSORPTION BY CALCIUM CARBIDE
According to Moissan, pure carbide is unaffected by nitro-
gen at 1200 C. 1 The discovery that nitrogen is absorbed by
commercial calcium carbide and barium carbide was patented
in 1895 by Adolph Frank and N. Caro. 2 In the case of barium
carbide 30 per cent forms cyanide in place of cyanamide, 3 while
in the case of calcium only a trace of cyanide is formed.
Since 1895 this reaction has been the subject of a number of
investigations. With regard to the temperature required, it
has been shown that finely powdered carbide must be heated
to from 1000 to 1100 C. to bring about complete transforma-
tion to cyanide. At 800 to 900 some nitrogen is absorbed,
but the reaction ceases before all the carbide is used up. 4 By
the addition of other calcium salts, such as calcium chloride, or,
to a less extent, calcium fluoride, complete nitrification can be
produced at 700 to 800 C. 5 That the commercial carbide
can be completely nitrified at 1100 is due to the presence
of calcium oxide. 6 Commercial calcium carbide containing 75
to 80 per cent carbide can be made to take up 85 to 90 per
cent of the theoretical amount of nitrogen, forming a black
mass of calcium cyanamide, lime, and carbon containing 20 to
23.5 per cent of nitrogen. 3 Pure calcium cyanamide contains
35 per cent nitrogen. The reaction by which it is made is
accompanied by a large evolution of heat, which of course
is advantageous in its manufacture. According to Caro, this
heat is sufficient to cause the reaction to proceed of itself when
once started. 7
The system consisting of calcium carbide, calcium cyanamide,
carbon, .and nitrogen, is monovariant, that is, for every tem-
perature there is a corresponding pressure of the nitrogen at
which equilibrium exists. This equilibrium has been meas-
1 C. R. 118, 501, (1894). 2 F ra nk, Z. f. angew. Ch. 19, 835, (1906).
8 Erlwein, Z. f. angew. Ch. p. 533, (1903).
4 Foerster and Jacoby, Z. f. Elektroch. 15, 820, (1909).
5 Bredig, Z. f. Elektroch. 13, 69, (1907).
6 Foerster and Jacoby, Z. f. Elektroch. 13, 101, (1907).
* N. Caro, Z. f. angew. Ch. 22, 1178, (1909).
THE FIXATION OF ATMOSPHERIC NITROGEN
ured between 1050 C. and 1450 C., and the results are given
in the plot in Figure 11 5. 8 If the initial pressure of nitrogen
lies in the region above the line, absorption of nitrogen takes
place, while if below, any calcium cyanamide present would
FIG. 115. Plot showing pressures and temperatures at which equilibrium of the
reaction CaC 2 +N 2 ^:CaCN2 + C exists. Pressures are in centimeters of mer-
cury ; temperatures in centigrade degrees.
decompose until the nitrogen produced brings the pressure up
to that corresponding to equilibrium, or until all of the cyan-
amide is used up.
The velocity of absorption of nitrogen is proportional to its
pressure, 9 assuming other conditions constant. At a constant
8 Thompson and Lombard, Proc. Am. Acad. 46, 247, (1910) ; Met. and Chem.
Eng. 8, 617, (1910). During proof reading the experiments of Le Blanc and
Eschmann, with results different from those above, appeared ; see Z. f. Elek-
troch. 17, 20, (1911). They find that the pressure depends on the nitrogen con-
tent of the solid phase as well as on the temperature.
Bredig, Fraenkel, and Wilke, Z. f. Elektroch. 13, 605, (1907).
268 APPLIED ELECTROCHEMISTRY
temperature, with a constant surface of carbide exposed, and
a given amount of nitrogen in a given volume, this law is
expressed by the differential equation :
where p is the pressure, t the temperature, and k is a constant.
Integrated this becomes
0.43 1 Pi
where p 2 and p l are the pressures at the beginning and end
respectively of the time interval t.
Calcium cyanamide acts in some cases as the calcium salt of
cyanamide : Ca = N C s N, and in others as the calcium salt
of the diimide
With superheated steam the nitrogen is changed to ammonia
according to the reaction 2
CaCN 2 + 3 H 2 = CaCO 3 + 2 NH 3
with a yield 99 per cent. 10 Dicyandiamid, a compound con-
taining 66 per cent nitrogen, can be made by treating calcium
cyanamide with water. It has the appearance of ammonium
chloride, and is probably formed by the following reaction :
2 CaCN 2 + 4 H 2 = 2 Ca(OH) 2 + (CNNH 2 ) 2 . n
Calcium cyanide can be made from technical calcium cyana-
mide by melting with a suitable flux, such as sodium chloride,
according to the following reversible reaction :
This use of calcium cyanamide is second in importance only to
its direct application as a fertilizer. 2
According to Frank 2 one horse power year can produce
enough carbide to absorb 772 kilograms of nitrogen, though
the value actually realized amounts to only 300 to 330 kilo-
10 Erlwein, Z. f. Elektroch. 12, 551, (1906).
11 Z. f. angew. Ch. p. 520, (1903).
THE FIXATION OF ATMOSPHERIC NITROGEN 269
grams. According to a later statement by Caro, 7 3 horse power
years is more than sufficient to absorb one metric ton of nitro-
gen, including the manufacture of the carbide and all the other
power required in the factory for the grinding and moving
apparatus, the Linde machines for liquefying air, and so forth.
Thus a factory with 12,000 horse power produces yearly 20,000
metric tons of calcium cyanamide containing 20 per cent nitro-
gen, corresponding to 4000 metric tons of nitrogen. It is in-
teresting to compare these data with the power required to
produce the corresponding amount of calcium carbide. An
average yield of carbide has been shown above to be 5.5 kilos
of 80 per cent carbide per kilowatt day, corresponding to 1500
kilos per horse power year. 376 kilograms of nitrogen would
have to be absorbed by this amount of carbide in order that the
product should contain 20 per cent nitrogen. This is a little
above the value 300 to 330 actually obtained as given by Frank.
If the statement of Caro is correct, and carbide is produced with
the efficiency assumed above, it means that 90 per cent of the
power in a cyanamide factory is used for producing the carbide
Nitrogen is obtained by the Linde process or by removing
the oxygen with hot copper. It must be free from oxygen, for
this would produce carbon monoxide, which decomposes both
carbide and cyanamide. 7 Caro states that moisture must be also
absent, though Bredig, Fraenkel, and Wilke's 9 experiments
showed that when the nitrogen was saturated with water vapor
at 22, a little more nitrogen was absorbed than when dry.
Besides lime and carbon, there are impurities in technical
cyanamide, consisting of nitrogen compounds, such as urea,
guanidine, and calcium carbamate. In fresh samples these
impurities are small in quantity, but increase on standing or
by the presence of water vapor. All of these substances are
easily assimilated by plants. 7
The manufacture of calcium cyanamide was begun on a large
scale in 1905 at Piano d'Orta, Italy, 10 and in 1908 there were
11 factories in Europe making this substance. 12 Norway and
i2Min. Ind. 17, 105, (1908).
270 APPLIED ELECTROCHEMISTRY
Sweden are unusually favorable localities for the nitrogen
industry on account of the large amount of cheap water power.
Recent estimates on power in these countries are as follows : 13
4,000,000 h. p.
400,000 h. p
5 000 000 h. p.
500 000 h p
The figures under " developed " refer to plants in operation or
under construction. There is a 20,000 horse power plant for
the production of cyanamide and calcium carbide at Odda,
Norway, having a capacity of 32,000 short tons of carbide and
12,500 tons of cyanamide per year. The nitrogen, which must
not contain over 0.4 per cent oxygen, is obtained by the Linde
process. The furnaces in which the carbide is heated with
nitrogen are charged with about 700 pounds and produce 2000
pounds of cyanamide containing 20 per cent nitrogen per week.
In 1909 this industry was introduced on this side of the
Atlantic by the American Cyanamide Company, which owns
the exclusive rights for manufacturing nitrolime in this country.
A factory is now in operation at Niagara Falls, Ontario. 14 The
product is to contain 12 to 15 per cent nitrogen, 10 per cent
carbon, and 25 per cent calcium sulphate. Free lime is to be
eliminated as is demanded by American trade.
3. THE OXIDATION OF NITROGEN
Priestley l was the first to observe that electric sparks in air
produced an acid, though he mistook it for carbonic acid.
Later Cavendish 2 repeated the experiments and showed the
true nature of the acid produced, which is now known to be a
mixture of nitrous and nitric acids. From the time of Caven-
13 Electrochem. and Met. Ind. 7, 212 and 360, (1909).
14 Met. and Chem. Eng. 8, 227, (1910).
1 Experiments and Observations on Different Kinds of Air, 4, 286. Preface
dated 1779. Also Ostwald, Elektrocheinie, p. 11.
a Phil. Trans. 75, 372-384, (1797). Also Alembic Club Reprints, No. 3, p. 39.
THE FIXATION OF ATMOSPHERIC NITROGEN
dish until within the last twenty years nothing of importance
was done toward explaining this phenomenon. Since 1890,
however, it has received considerable attention, so that now,
principally due to the work of Nernst and Haber, the conditions
under which the reaction N 2 + O 2 ^ 2 NO takes place are well
Nernst and his assistants have measured the thermal equilib-
rium concentrations of nitrogen, oxygen, and nitric oxide at
different temperatures with the results in Table 32. 3
Per cent by Volume of Nitric Oxide in the Equilibrium Mixture formed from Air
0.52 to 0.80
The values in the third column were computed by the Van't
Hoff equation, with Berthelot's value of 21,600 calories for
the heat of the reaction. These experiments show that at the
temperatures given the velocity of decomposition is so low that
the gas can be cooled without decomposition of the nitric oxide
The free energy of the reaction is given by the equation 4
= Q -ET log-
+ 2.45 T,
in which Q = 21,600 calories. By means of this equation
the per cent of nitric oxide corresponding to the equilibrium
at any temperature can be computed by placing the right-hand
Z. f. anorg. Ch. 49, 213, (1906).
* Haber, Thermodynamics of Technical Gas Reactions, p. 105, (1908).
side equal to zero, which is the equilibrium condition. The
experiments of Finckh were carried out by exploding air mixed
with detonating gas ; the others by drawing air through plati-
num or iridium tubes heated electrically. The good agreement
between the calculated and observed values shows that at least
in these experiments the nitric oxide formed is due only to the
high temperature, as the concentration is that required by
This reaction is bimolecular between 650 C. and 1750 C., 5
that is to say, it should be written N 2 + O 2 = 2 NO. Le Blanc
and Niiranen, however, have found that above 3000 C. the
reaction is monomolecular. 6 Tables 33 and 34 give the veloci-
ties of the reaction in both directions at different temperatures. 6
Time in Minutes necessary to decompose Pure Nitric Oxide at Atmospheric Pres-
sure, Half into Nitrogen and Oxygen
TIME IN MINUTES
TIME IN MINUTES
7.35 10 3
1.21 10- 3
5.80 10 2
8.40 10- 5
4.43 10 1
5.76 10- 6
3.92 10- 7
2.47 10- 1
3.35 10~ 8
1.47 lO- 2
2.25 10- 9
Time required to produce from Air One Half the Possible Amount of Nitric Oxide
TIME IN MINUTES
TIME IN MINUTES
1.81 10 8
1.77 10~ 4
5.90 10 1
8.75 10- 6
5.75 10- 7
8.43 10- 2
3.10 10- 8
5 Jellinek, Z. f. anorg. Ch. 49, 229, (1906).
6 Z. f. Elektroch. 13, 303, (1907).
THE FIXATION OF ATMOSPHERIC NITROGEN
From these results it would appear that the best yield of
nitric oxide would be obtained by heating the gas to the
highest temperature from which it could be chilled so suddenly
that decomposition would not take place. It has been shown,
however, that nitric oxide can be produced by the silent dis-
charge of electricity where there is very little elevation of
temperature. 7 This fact suggested to Haber and Koenig 8 the
possibility of obtaining better yields by using a comparatively
cool arc, which could be realized by inclosing it in a tube
surrounded by water. Below 3000 C. any oxide produced by
the impact of electrons would not be decomposed rapidly by
the heat even if the concentration due to the electrical effect
were greater than that due to the thermal. In fact they found
that by using a cooled arc and by reducing the pressure to the
most favorable value of 100 millimeters, concentrations of
nitric oxide were obtained which could be explained thermally
only on the assumption that the thermal equilibrium correspond-
ing to over 4000 absolute had been obtained and that the gas
had been chilled suddenly enough to preserve it. Such a high
Concentrations of Nitric Oxide obtained at 100 mm. Pressure by an Arc inclosed in
a Cooled Tube
INITIAL GAS MIXTURE IN
PER CENT BY VOL.
PUTED TEMP. ABS.
IN PER CENT
_) O 2 ft N^2
7 Warburg and Leithauser, Ann. d. Phys. (4) 20, 743, (1906), and 23, 209,
8 Z. f. Elektroch. 13, 725, (1907).
274 APPLIED ELECTROCHEMISTRY
temperature in their arc seemed impossible ; consequently the
oxide must have been produced directly by the impact of ions.
Table 35 gives the concentrations of nitric oxide obtained with
the temperature corresponding, on the improbable assumption
that this concentration corresponds to a thermal and not to an
electrical equilibrium. The temperatures were computed both
by Haber's formula given above and by the Van't Hoff formula
as used by Nernst.
In later experiments as high as 17.8 per cent nitric oxide was
obtained. 9 It was further found that the same concentration
is obtained under similar conditions from either nitric oxide
or from air and oxygen, showing that we have in this case
an electrical equilibrium. If the temperature is too high, the
electrical equilibrium is obliterated by the thermal. On the
other hand, the electrical energy necessary to produce ioniza-
tion increases considerably when the temperature falls below
white heat. There will therefore be a most favorable region
of temperature within which the nitric oxide produced by the
impact of ions will not be decomposed and when too much
electrical energy is not required for ionization. 8 It would,
therefore, seem that the best way to try to obtain better re-
sults is to employ a cool arc rather than by attempting to heat to
a higher temperature and chill more suddenly.
The energy efficiency was not determined in these experi-
ments. In later ones, 10 with a cooled arc, the efficiency, when
the concentration of the nitric acid obtained was 3.4 per cent,
was 57 grams of nitric acid per kilowatt hour, or 500 kilo-
grams per kilowatt year of 365 x 24 hours. With a cooled
arc and a direct current, Holweg and Koenig n obtained
nitric acid at a concentration of 2.5 per cent and an efficiency
corresponding to 80 grams of nitric acid per kilowatt hour,
the most favorable energy efficiency ever reached. Increas-
ing the pressure above atmospheric does not increase this
Z. f. Elektroch. 14, 689, (1908). 10 Z. f. Elektrock. 16, 795, (1910).
" Z. f. Elektroch. 16, 809, (1910).
12 Haber and Holweg, Z. f. Elektroch. 16, 810, (1910). *
THE FIXATION OF ATMOSPHERIC NITROGEN
On cooling down, the colorless nitric oxide changes to the
brown dioxide of nitrogen, since the reversible reaction
NO + \ r 2 ^ N0 2
is displaced from left to right on cooling.
Table 36 shows how the dissociation of nitrogen dioxide is
affected by the temperature : 13
PRESSURE IN CENTIMETERS
PER CENT OF NO 2 DECOMPOSED
It will be interesting to compute from a purely thermal
standpoint the energy necessary to produce nitric acid and to
compare this result with those actually found by different ex-
perimenters. Assuming the temperature of the high tension
arc to be 4200 C., the calculation is as follows. 14 From the
equation given above at this temperature
and if the original mixture is air, the final composition is :
NO O 2 N 2
10 per cent 16 per cent 74 per cent
Ten moles of nitric oxide with air and water yield 630 grams of
nitric acid. Therefore, in order to get this amount of acid,
100 moles must be heated to 4200 C., besides which 10 x 21,600
calories must be supplied for the reaction. Assuming the spe-
18 Nernst, Theoretische Chemie, p. 455, 6th ed. See also Bodenstein and Kata-
yama, Z. f. Elektroch. 15, 244, (1909).
14 Haber, Thermodynamics of Technical Gas Reactions, p. 268.
276 APPLIED ELECTROCHEMISTRY
cific heat of the permanent gases to be 6.8 -f 0.0006 calories
per mole, the total energy will be :
100 (6.8 + 0.0006 x 4200) 4200 + 216,000 = 4,130,000 calories.
This corresponds to 4.71 kilowatt hours for 630 grams of nitric
acid, or 134 grams per kilowatt hour. If the arc were 1000
lower, the result would be 93.5 grams per kilowatt hour.
The results obtained with a cooled arc are not due to ther-
mal equilibrium, and of course have no relation to this calcula-
tion. Unless special precautions were taken to use a cooled
arc, the results may be assumed to be due to thermal and not
to electrical causes. This is the case in the following examples.
Lord Rayleigh 15 obtained an absorption of 21 liters an hour
with 0.8 kilowatt, using a mixture of 9 parts of air and 11 of
oxygen. This corresponds to 46 grams of pure nitric acid per
kilowatt hour, assuming the gas was measured at 20 C. and at
atmospheric pressure. McDougall and Howies 16 with an ar-
rangement similar to that of Lord Rayleigh obtained 33.5 grams
of nitric acid per kilowatt hour. McDougall and Howies were
the first to make a small experimental plant for the production
of nitric acid from the air. 17 It seems not to have got beyond
the experimental stage, however.
The first 18 attempt to carry out the oxidation of nitrogen on
a commercial scale was that of the Atmospheric Products Com-
pany at Niagara Falls, using the patents of Bradley and Love-
joy. Their first apparatus 19 was similar to that of McDougall
and Howies and consisted in a number of small compartments
in which an arc was formed between electrodes in the form of a
hook at the points nearest together, as shown in Figure 116. The
arc then ran along the electrodes, thereby becoming longer,
until it went out, whereupon the arc was formed again. This
i 5 Journ. Chem. Soc. 71, 181, (1897).
, 16 Memoirs and Proceedings of the Manchester Literary and Phil. Soc. (IV)
44, 1900, No. 13.
17 Huber, Zur Stickstoff Frage, p. 41, Bern, (1908).
18 Donath and Frenzel, Die Technische Ausinetzung des Atmospharischen
Stickstoffes, p. 126, (1907).
U. S. Pat. 709,867, (1902).
THE FIXATION OF ATMOSPHERIC NITROGEN
arrangement was supplanted by a single apparatus, shown in
Figures 117 and 118, in which 6900 arcs were formed per
second. 20 This consisted in an iron cylinder 5 feet high, 4 feet
in diameter, in the center of which was a rotating shaft carry-
ing a series of radial arms, the ends of which were tipped with
FIG. 116. First apparatus of
Bradley aud Lovejoy
platinum. Six rows of 23 inlet wires projected through the
cylinder and terminated in a platinum hook. As the radial
arms rotated, their platinum tips passed the hooks on the inlet
wires, coming within one millimeter of touching at the nearest
point. An arc was formed which was drawn out from 4 to 6
inches before going out. The arms were so arranged that the
20 J. W. Richards, Electroch. Ind. 1, 20, (1902) ; U. S. Pat. 709,868, (1902).
arcs between them and the inlet wires were formed successively
rather than simultaneously. The central shaft made 500 rota-
tions per minute. Each inlet wire had in series with it an in-
duction coil 12 inches long and 5 inches in diameter, wound
with very fine wire and immersed in oil. The self-induction of
the coil caused the spark to be drawn out to a greater length
than would be possible without induction. A direct current
FIG. 117. Vertical section of final
apparatus of Bradley and Lovejoy
generator was especially designed for this plant, giving 8000
volts and 0.75 ampere. Air passed in at the rate of 11.3 cubic
meters per second and came out of the cylinder containing 2.5
per cent nitric oxide. 21 The yield is said to have been one
pound of acid per 7 horse power hours, or 87 grams per kilo-
watt hour. The process was not successful, however, and the
company was forced to give up the experiments in 1904.
21 Haber, Z. f. Elektroch. 9, 381, (1903).
THE FIXATION OF ATMOSPHERIC NITROGEN
Though the yield compared favorably with the calculations
given above, the . apparatus was very complicated and subject
to considerable wear. The iron drum corroded rapidly in spite
of the inside coating of asphalt paint. 18
The first successful process for oxidizing nitrogen on a com-
mercial scale is that of Birkeland and Eyde. A factory for
carrying it out was started at Notodden, Norway, in May, 1905. ^
The high voltage flame is formed between two electrodes con-
sisting of water-cooled copper tubes 1.5 centimeters in diameter
FIG. 118. Horizontal section of final apparatus of Bradley and Lovejoy
with 0.8 centimeter between the ends. An alternating current
of 50 cycles per second is supplied to the electrodes at 5000
volts. In order to spread the flame over a large area an
electromagnet is placed at right angles to the electrodes so that
the terminals lie between the poles of the magnet. The
voltage is sufficiently high to cause the flame to form of itself
between the electrodes at their nearest points, whereupon the
magnetic field causes the ends of the flame to travel along the
electrodes until the current is reversed. A new flame is then
started on the other side of the electrodes. When the furnace
22 Birkeland, Trans. Faraday Soc. 2, 98, (1906).
is running properly a flame is formed at each reversal of the
current every ^ of a second, though if the distance between
FIG. 119. Electric disc in the furnace of Birkeland and Eyde
the electrodes is too short or the magnetic field too strong,
several hundred flames may be started during one period. The
magnetic field is
J V 4000 to 5000 lines
per square centi-
meter at the center.
The result of this
combination is an
electric disk flame,
as shown in Figure
119. This is in-
closed in a narrow
iron furnace lined
with fire brick, form-
ing a chamber from
5 to 15 centimeters
wide, shown in
Figure 120. Air
120. - Vertical section of furnace of Birkeland I* 8808 in tlir U S h
and Eyde the walls and leaves
THE FIXATION OF ATMOSPHERIC NITROGEN 281
the furnace at a temperature between 600 and 700 C., con-
taining one per cent of nitric oxide. From the furnace the
gases pass through a steam boiler in which they are cooled
to 200 C., and then through a cooling apparatus in which
their temperature is reduced to 50 C. They then enter
oxidation chambers with acid proof lining, where the reaction
NO + $ O 2 = NO 2 is completed.
The next step is to absorb the nitrogen dioxide. This is
done in two sets of five stone towers whose inside dimensions
are 2 x 2 x 10 meters. The first four towers are filled with
broken quartz over which water trickles. The fifth tower is
filled with brick, and the absorbing liquid is milk of lime, giving
a mixture of calcium nitrate and nitrite. Nitric acid is
formed in the first four towers with concentrations as follows :
FIRST SECOND THIRD FOURTH
50 % HXO 3 25 % HNO 3 15% HNO 3 5% HNO 3
The liquid from the fourth tower is raised by compressed air
to the top of the third, that from the third to the top of the
second, and so on until fifty per cent nitric acid is formed.
Some of this acid is used to decompose the nitrate-nitrite
mixture from the fifth tower. The nitric oxide thereby
evolved is sent into the absorbing system again. About 97
per cent of the entire quantity of nitrous gases passed through
the absorbing system is absorbed. 23 The resulting solution of
calcium nitrate and the rest of the stored-up acid is treated in
another set of tanks with lime, producing neutral calcium
nitrate. This is evaporated in iron by the steam from the
boilers above mentioned till a boiling point of 145 C. is reached,
corresponding to 75 or 80 per cent nitrate and containing 13.5
per cent of nitrogen. This is poured into iron drums of 200
liters capacity, where it solidifies. Another method is to
crystallize from a boiling point of 120 C. This yields calcium
nitrate with four molecules of water.
In 1906 at the Notodden Saltpeter Manufactory there were
three 500-kilowatt furnaces in constant activity. The volume
28 Eyde, Electrochem. and Met. Ind. 7, 304, (1909).
282 APPLIED ELECTROCHEMISTRY
of air treated was 75000 liters per minute. The yield was
about 500 kilograms of pure nitric acid per kilowatt year, or
57 grams per kilowatt hour.
In place of the smaller furnaces those now used absorb 1600
kilowatts, of which 35 are now in operation at Notodden, 8 in
series. The disk flame has a diameter of 2 meters and a
thickness of 10 centimeters. 24
During the year 1908 the profits of the Notodden factory were
25 per cent of the total receipts, amounting to 500,000 krone,
or $ 135,000. M The company using the Birkeland-Eyde process
has combined with the Badische Anilin und Sodafabrik, which
has developed another furnace, described below, so that the re-
sults of a factory under construction at Notodden in 1909 will
decide which furnace will be the one for the final large plant. 25
Up to February, 1909, 16,000,000 had been invested at Notodden
and Svalgfos and on the rivers Rjukan and Vamma. By the
end of 1910 these plants will be completed and the investment
will amount to fl^OOO^OO. 25
The furnace of the Badische Anilin und Sodafabrik of
Ludwigshafen, Germany, was invented in 1905 by Schonherr
and Hessberger. 26 An alternating current arc is very easily
extinguished, especially if air is blown across it. The principle
underlying this furnace is that an alternating current arc loses
its unstable character and becomes as quiet as a candle if a cur-
rent of air is passed around it in a helical path. With this
method of air circulation the arc may be included in a metallic
tube without risk of its coming in contact with the sides of the
tube. A cross section of the apparatus is shown in Figure 121.
It consists of a number of concentric vertical iron tubes. The
electrode at the bottom is an iron rod adjustable within a water-
cooled copper cylinder. The iron is slowly eaten away, and is
fed in at about the rate of one electrode in three months. The
electrode Z is for starting the arc by bringing it in contact with
24 Birkeland, Electrochem. and Met. Ind. 7, 305, (1909).
25 Eyde, Z. f. Elektroch, 15, 146, (1909).
2^ Electrochem. and Met. Ind. 7, 245, (1909) ; Trans. Am. Electrochem. Soc.
16, 131, (1909).
FIXATION OF ATMOSPHERIC NITROGEN 283
E. There is of course an induction coil
in series with the arc to make it steady
\ and prevent the current from being too
large on starting. When Z is drawn
back the arc is formed between E and
* the walls of the tube. The air then
| drives it up along the tube until it
| reaches the other water-cooled end, JT,
within which the arc terminates. 6r r
2 6r 2 , and 6r 3 are peep holes for observing
! , the ends of the arc. In the 600 horse
1 .- power furnaces at Kristianssand, Nor-
bj> way, the arc is 5 meters long, and 7
8 | meters in the 1000 horse power fur-
H ' naces. The circulation of the air is
g evident from the figure.
The plant at Kristianssand, the fur-
3 nace room of which is shown in Figure
122, has been in operation since the
autumn of 1907. Three-phase currents
4 are used, and the furnaces are connected
in star. The power factor varies between
H 0.93 and 0.96. It is estimated that 3 per
cent of the power is used in the formation
of nitric oxide, 40 per cent is recovered
in the form of hot water, 17 per cent is
lost by radiation, 30 per cent is used in
the steam boiler, and 10 per cent is
removed by water cooling after the
erases have passed the steam boiler.
The nitric oxide is absorbed by milk of
lime. The final product is calcium
nitrite containing 18 per cent nitrogen.
The yield per kilowatt hour is not given.
A third process for the fixation of at-
mospheric nitrogen, invented by H. and
G. Pauling, is carried out near Inns-
bruck, Tirol, by the " Salpetersaure-Industrie-Gesellschaft." 27
The arcs are produced between curved electrodes, as shown in
Figure 123. The arc is lighted where the electrodes are near-
est together, is blown upwards by the hot air rising between
FIG. 122. Furnace room at Kristianssaud
the electrodes, and is broken every half period of the alternating
current. Another arc is then formed, and so on. In Figure 123
c represents two thin adjustable blades for starting the arc.
Air is blown in through the tube e. The electrodes are iron
pipes, water-cooled and separated by about 4 centimeters at
, 27 Electrochem. and Met. Ind. 7, 430, (1909).
THE FIXATION OF ATMOSPHERIC NITROGEN
their nearest point. Their life is about 200 hours. With a
400 kilowatt furnace of 4000 volts the length of the flame is
about one meter. Cooling is produced by passing cold air into
the upper part of the flame from the side. The concentration
of the nitric oxide is about 1.5 per cent. The furnaces used
have two arcs in series.
Six hundred cubic
meters of air per hour
pass through the fur-
nace, excluding the
cooling air. The
yield is 60 grams of
nitric acid per kilo-
watt hour. At pres-
* FIG. 123. Electrodes in lurnace of
ent there are 24 fur- H. and G. Pauling
naces in operation at
Innsbruck, having a capacity of 15,000 horse power. The
products are nitric acid and sodium nitrite. Two other plants
for carrying out this process, each of 10,000 horse power, are
in course of erection, one in southern France and the other in
A number of other furnaces for the oxidation of nitrogen
have been invented, but their descriptions are omitted here
because they are not in operation on a commercial scale.
4. THE SYNTHESIS OF AMMONIA
The third method of fixing nitrogen, that has just recently
been taken up by the Badische Anilin und Sodafabrik, 1 is to
make it combine directly with hydrogen to form ammonia, ac-
cording to the reversible reaction :
This reaction takes place from left to right with the evolution
of about 12,000 calories, 2 so that the quantity of ammonia gas in
the equilibrium mixture decreases as the temperature rises.
1 Haber, Z. f. Elektroch. 16, 242, (1910).
2 Landolt and Bernstein's Tables, 3d ed. p. 427.
The velocity of the reaction, on the other hand, of course in-
creases with the temperature, but does not reach a value that
adjusts the equilibrium rapidly below a temperature of 750 C. 3
The composition of the equilibrium mixtures for different tem-
peratures and two different pressures, when the free hydrogen
and nitrogen are present in the same proportion as in ammonia,
is given in Table 37. 4
VOL. PER CENT
VOL. PER CENT
0.144 to 0.152
0.0048 to 0.0051
It is evident from this table that unless some catalytic agent
can be found that would give the reaction high velocity at a
temperature considerably below 750, very little ammonia could
be obtained at atmospheric pressure. Since, however, there is
a decrease in volume when ammonia is formed from an equiva-
lent amount of nitrogen and hydrogen, there must be an in-
crease in the relative amount of ammonia in an equilibrium
mixture when the pressure is increased. It is evident from
the table that the volume per cent of ammonia in such a mixture
is directly proportional to the pressure, as long as the relative
amounts of free hydrogen and nitrogen are kept constant.
Jost 5 has obtained somewhat lower values for the amount
of ammonia in the equilibrium mixture. Table 38 gives his
results obtained at a total pressure of one atmosphere, and those
of Haber taken from the table above for comparison.
Haber's results at one atmosphere are in good agreement
with the values calculated from his results at 30 atmospheres,
and therefore are more reliable than Jost's.
8 Haber, Thermodynamics of Technical Gas Reactions, p. 202, (1908).
* Haber and Le Rossignol, Z. f. Elektroch. 14, 193, (1908).
5 Z. f. Elektroch. 14, 373, (1908).
THE FIXATION OF ATMOSPHERIC NITROGEN
VOLUME PER CENT NH 8
0.0048 to 0.0051
Haber lias subsequently developed this process further and
showed in a lecture 1 a small apparatus working at 185 atmos-
pheres that produced hourly 90 grams of liquid ammonia. In
the earlier experiments finely divided iron on asbestos was used
as a catalyzer, but in these later experiments, uranium was
substituted for iron. This method is said to require compara-
tively little power, and will therefore not be confined to places
where cheap water power is available. No numerical values of
the efficiency of this method, however, are given.
Having described the three general methods of fixing atmos-
pheric nitrogen now in operation, it will be interesting to com-
pare the actual amounts of nitrogen fixed for a given amount
of power by the three methods. This is possible only for the
absorption by carbide and the direct oxidation.
Since 12,000 horse power or 8850 kilowatts can fix 4,000,000
kilograms of nitrogen l per year as calcium cyanamide, one kilo-
watt hour corresponds to 51.6 grams of nitrogen. The yield
by the Birkeland-Eyde process is about 57.1 grams of pure
nitric acid per kilowatt hour, 2 corresponding to 12.7 grams of
nitrogen. The cyanamide process therefore fixes about four
times as much nitrogen as the direct oxidation for the same ex-
penditure of power.
i Frank, Z. f. angew. Ch. 19, 835, (1906).
2 Birkeland, Trans. Faraday Soc. 2, 98, (1906); Haber, Z. f. Elektroch. 10,
THE PRODUCTION OF OZONE
1. GENERAL DISCUSSION
IN 1785 Van Marum observed that oxygen through which
an electric spark had passed had a peculiar odor, and that it at
once tarnished a bright surface of mercury. 1 Nothing was
done to throw light on this phenomenon until 1840, when it
was investigated by Schonbein. He had observed for a num-
ber of years previously that during the electrolysis of aqueous
solutions an odor is produced in the gas evolved at the anode
similar to that resulting from the discharge of electricity from
points. 2 He described a number of the properties of this sub-
stance, and suggested the name ozone, from 6'&>i>, meaning
smelling. For many years the chemical nature of this oxidiz-
ing principle was unknown, but it was found eventually, after
a great number of investigations, to be simply condensed
oxygen with the formula O 3 .
The formation of ozone from oxygen is an endothermic
reaction. The heat absorbed in the production of one mole
of ozone, as determined by different investigators, is given
in the following table : 3
Berthelot, indirect, 1876 29,800 calories
Mulder and v. d. Meulen, indirect, 1883 . . . 33,700 calories
v. d. Meulen, indirect, 1882 32,800 calories
v. d. Meulen, direct, 1883 36,500 calories
Jahn, direct, 1908 . 34,100 calories
1 Roscoe and Schorlemmer, Treatise on Chemistry, 1, 256, (1905).
2 Pogg. Ann. 50, 616, (1840).
8 Stephan Jahn, Z. f. anorg. Ch. 48, 260, (1905).
THE PRODUCTION OF OZONE 289
Since heat is absorbed in the production of ozone, thermo-
dynamics requires that the equilibrium existing in a mixture of
oxygen and ozone be displaced in the direction of a greater
ozone concentration by an increase in the temperature of the
mixture. In order to prove this experimentally, it is necessary
to heat the oxygen to a temperature high enough to produce a
measurable quantity of ozone, and then, by cooling suddenly, to
prevent the decomposition of the ozone formed. This has been
done by blowing air or oxygen against a hot pencil, such as is
used in a Nernst lamp, 4 and also by dipping a hot Nernst
pencil, or hot platinum, in liquid air. 5
The free energy decrease which accompanies the decomposi-
tion of ozone into oxygen has been determined from potential
measurements. 6 At C. the potential of the cell O 3 | electro-
lyte H 2 equals 1.90 volts, and that of the cell O 2 | electrolyte H 2
equals 1.25 volts. The reactions which take place in these two
cells, with the corresponding free energy changes, are therefore
given by the following equations :
2 O 3 + 2 H 2 = 2 O 2 + 2 H 2 O + 4 F x 1.90 joules,
O 2 + 2 H 2 = 2 H 2 O + 4 F x 1.25 joules,
where F is the electrochemical equivalent. The difference
between these two equations gives :
2 O 3 = 3 O 2 + 4 F x 0.65, or O 3 = f O 2 + 30,000 calories.
From this result the following equilibrium concentrations at
high temperatures may be calculated :
Temperature on absolute scale . . 1000 1400 1800 2200
Pres. ozone in atmospheres, in equi-
librium with oxygen at one
atmosphere 0.000029 0.0032 0.038 0.18
The above results are only approximate, for the very divergent
values inclosed in parentheses are within the experimental
4 Fischer and Marx, B. B. 40, 443, (1907).
5 Fischer and Braemer, B. B. 39, 996, (1906).
6 Stephan Jahn, Z. f. anorg. Ch. 60, 332, (1908).
290 APPLIED ELECTROCHEMISTRY
It will be seen from these results that ozone, in the concen-
trations ordinarily prepared, amounting to several per cent by
volume, is in a state of unstable equilibrium, and it conse-
quently decomposes slowly on standing. This reaction is
lii molecular ; 7 that is,
'J' dn = -kn* dt,
where n is the number of moles per cubic centimeter, k is a
constant, and t is the time. The velocity of this reaction is
given in Table 39. ft is the number of grams of ozone in one
liter that would decompose per minute if its initial concentra-
tion were one gram per liter.
At 16 one per cent of pure ozone would decompose in 1.7
hours, and 50 per cent in 167 hours. These values apply to
ozone in contact with concentrated sulphuric acid, over which
the pressure of water vapor is 0.0021 millimeter of mercury.
If the pressure of water vapor is 0.154 millimeter, the velocity
of decomposition at lOO^is found to be 22 per cent greater.
The decomposition of ozone takes place in steps, the reaction
whose velocity is measured being
O + 3 = 2 2 . 8
Ozone may be produced by the action of ultra-violet light,
and of the silent discharge of electricity on oxygen ; by heat-
ing and suddenly chilling oxygen, and by electrolysis. While
the silent electric discharge is the only method used commer-
cially for the manufacture of ozone, it will be interesting to
7 Warburg, Ann. d. Phys. 9, 1286, (1902), and 13, 1080, (1904).
8 Jahn, Z. f. anorg. Ch. 48, 260, (1005).
THE PRODUCTION OF OZONE 291
compare the yield per kilowatt hour attained by the silent dis-
charge with some of the other methods. By blowing air
against a hot Nernst pencil, the yield was found to be one
gram 4 per kilowatt hour ; and by dipping hot bodies in liquid
air, about 3.5 grams. 5 The concentration of the ozone in bot'^i
cases was less than three per cent. By electrolyzing solutions
of sulphuric acid of specific gravity between 1.075 and 1.1
with a water-cooled platinum anode, as high as 17 per cent by
weight of the oxygen given off at the anode has been obtained
in the form of ozone. 9 Assuming three volts sufficient to
electrolyze the solution, the yield in oxygen per kilowatt hour
would be 10 grams, and if 17 per cent of this were ozone, the
yield would be only 1.7 grams per kilowatt hour. When com-
pared with 70 grams per kilowatt hour, the yield obtained with
the silent discharge, these methods are seen to be inefficient
from an economical standpoint, though if a high concentration
is desired, this can be best obtained by electrolysis.
There are two distinct forms of silent discharge of electricity,
which differ in their appearance, in the amount of ozone which
they produce, and in the current which is required to produce
them. 10 If a point one centimeter distant from a plate con-
nected to earth is charged negatively to 7000 volts in air, a
bluish light surrounding the point can be seen with the naked
eye. If the potential is raised, a reddish broad brush appears,
separated from the bluish light by a dark space, while the oppo-
site plate remains dark. These different parts of the discharge
correspond to what is observed in a vacuum tube in which the
air is at a pressure of a few millimeters of mercury. The
bluish light corresponds to the negative glow, the dark space
to the Faraday dark space, and the reddish light to the positive
column of light.
With a positively charged point and a low potential differ-
ence, a reddish envelope of light is first observed, from which
a brush is developed on increasing the potential. The ability
9 Fischer and Massenez, Z. f. anorg. Ch. 52, 202, (1907).
10 Askenasy, Technische Elektrochemie, p. 240, (1910); and Warburg, Ber. d,
deutsch. phys. Ges., (1904), 209.
to form this brush is important for the ozone formation, and is
lost by points after use. In place of it a spark discharge is
produced ; but the brush discharge can be
produced even on old points by placing a
spark gap 0.1 millimeter long before the
If the discharge takes place between paral-
lel conducting plates, either one or both being
covered with a dielectric, the case is more
complicated. 11 This type of ozonizer was
devised by W. von Siemens and is usually
called by his name. 12 Siemens's original ozon-
izer consisted of concentric tubes, as shown
in Figures 124 and 125. Two such tubes,
with the sides a and d covered with a conduc-
tor, such as tin foil, may be looked upon as a
series of condensers connected in series, with
an ohmic resistance in parallel with one of
them. In this case there would be three con-
densers : ab, be, and cd ; while if the inner
tube is bare metal there would be only two :
be and ab. When the space be is filled with a
perfect insulator or with a perfect conductor,
the current has its small-
est or its largest value, re-
spectively. In both cases
the apparatus is a perfect
condenser and absorbs no
energy, since cos <f> = 0,
FIG. 124. Longi- &J ' . V. '
tudinai section of where $ is the angle of
Siemens's original p nase difference between FIG. 125 Transverse sec-
the voltage and the cur- *" M .'.o,ir
rent. For an average conductivity in 6<?, such as a gas can
have, cos < assumes its largest value. In actual practice all
11 Askenasy, p. 242 ; Warburg and Leithauser, Ann. d. Phys. 28, 1 and
12 Fogg. Ann. 102, 120, (1857).
THE PRODUCTION OF OZONE 293
possible values of cos <f> between and 1 may occur. With
increasing current strength cos $ decreases, probably because
the resistance of the gas decreases with increasing current. If
the frequency of the alternating current increases, cos <f> in-
creases and approaches 1. High frequencies, between 200 and
500 per second, should therefore be used. Ozonizers with one
tube bare metal are better than those with both tubes glass,
for cos (j) is larger, and a larger current passes, for a given vol-
tage, than in a glass apparatus of the same dimensions.
If an alternating electromotive force is applied between a
point electrode and a plate connected to earth, the positive
brush appears. By means of a rotating mirror the positive
and negative light can be seen alternately on the point, and its
appearance is not much changed when the plate is covered with an
insulator. 11 If a Siemens apparatus has a large current passing,
a uniform luminosity appears in the space between the elec-
trodes, but if the current density is sufficiently lowered, brushes
are formed at single points on the electrodes. From the ap-
pearance of these discharges, there is no doubt that the same
process takes place in the Siemens apparatus as in one with
point and plate electrodes, except that in the Siemens ozonizer
the effects on positive and on negative points are superimposed,
as in the case of a direct current between two metallic points.
The production of ozone by the silent discharge of electricity
may be considered from the following different points of view :
(1) the maximum concentration that can be obtained, (2) the
maximum number of grams that can be produced per coulomb
of electricity, and (3) the maximum number of grams per unit
of power. The latter consideration is, of course, of the most
technical importance. As stated above, ozonizers with point
electrodes give different results, depending on whether the
points are positive or negative to the plate. The Siemens ozon-
izer is a third case to be considered. The amount of ozone
produced per coulomb is therefore a variable quantity, and fol-
lows no known law, such as we have in Faraday's law in the
case of electrolysis. In the absence of such a law, it will be
necessary to show what the yield is under different conditions
and how this is affected by changing the conditions. In ordei
to give a systematic survey of this subject, the maximum con-
centration will first be discussed for the three cases enumerated
above, and the yields per unit of electricity
and per unit of power, including the factors
that affect them, will then be taken up in the
following order, (1) for points negative,
(2) for points positive, and (3) for Siemens
The Maximum Concentration
The silent discharge of electricity has a
deozonizing effect on ozone, as well as an
ozonizing effect on oxygen. The ozonizing
effect of the discharge is proportional to the
concentration of the oxygen, and the deozo-
nizing effect to that of the ozone. In other
words, this reaction follows the mass action
law. If the discharge passed for an infinite
time, a limiting concentration of ozone would
be reached, at which the amount decomposed
per second would equal the amount pro-
duced. These two different effects have
been studied separately by E. Warburg. 1
The experiments were carried out in the
apparatus shown in Figure 126. The ozon-
izer was connected with an auxiliary ves-
sel H by a capillary tube filled with sulphuric
acid to a proper distance above B. and
H each had a volume of a little over one
cubic centimeter. The point electrode e l
was a platinum wire 0.05 millimeter in diam-
eter; the earth electrode 2 was a platinum
wire 0.5 millimeter in diameter bent in the
form of a U to increase the surface. After filling the appara-
FIG. 126. Apparatus
for determining the
ble concentration of
i Ann. d. Phys. 9, 781, (1900).
THE PRODUCTION OF OZONE
tus with oxygen and sealing off at ^, 0, and 5, the rate at which
ozone was produced, and the concentration, could be observed
by the change in the height of the sulphuric acid in the ma-
nometer. Table 40 gives the results obtained with e l connected
to the negative pole of an electrostatic machine and e z through
a galvanometer and to earth. is a constant proportional to
the rate of formation of ozone at a given temperature, and a is
a constant proportional to its decomposition.
PEE CENT OZONE BY
/3 = A CONSTANT PRO-
PORTIONAL TO KATE
o = A CONSTANT PRO-
PORTIONAL TO THE RATE
This table shows that the maximum concentration decreases
as the temperature rises, and that this is due to the increasing
decomposing effect of the discharge, and not
to a smaller ozonizing effect. This is evident
from the values of a and /3. The spontaneous
decomposition of the ozone was negligible.
The ozonizer was then replaced by the one
shown in Figure 127 with a volume of 7.5
cubic centimeters. The point electrode e
consisted of a platinum wire 0.05 millimeter FIG. 127. Ozonizer
thick, and the earth electrode e 2 was a half
cylindrical platinum plate. In this ozonizer
the positive, as well as the negative, point discharge could be
obtained. In both cases faint, luminous points were visible in
the dark on the thin wire, while the earth electrode remained
dark. With a current of 33 microamperes the results in Table
41 were obtained.
Point Electrode Negative
TION PEE CENT OZONE
/3= CONST. PROPORTIONAL TO
BATE OP FORMATION
a = CONST. PROPORTIONAL
TO KATE OF DECOM-
Point Electrode Positive
From these results it is evident (1) that the maximum
concentration with the point negative is about three times as
great as with the point positive ; (2) that this is due to the
greater ozonizing effect of the discharge when the point is
negative, since the deozonizing effect is approximately the same
in both cases ; and (3) the temperature effect is the same for
the positive as for the negative point discharge.
For the Siemens type of apparatus the limiting concentration
of ozone produced from 96 per cent oxygen diminishes slightly
with increasing current, as shown by the following table : 2
AMPEKKS x 10 8
GRAMS PER CUBIC
PER CENT BY
2 Warburg and Leithauser, Ann. der Phys. 28, 31, (1909).
THE PRODUCTION OF OZONE
FIG. 128. Experimental ozonizer
Fig. 129. Experimental ozonizer
The limiting concentration is evidently a quantity that
varies with the apparatus used. The highest value obtained
is 211 grams per cubic meter, or 10.1 per cent by volume. 3
Yield per Coulomb for Negative Point Electrode
In order to produce the maximum amount of ozone per
coulomb, the deozonizing effect of the electric discharge must
be excluded. This may be ac-
complished by passing the oxy-
gen through the ozonizer so
rapidly that the concentration
of the ozone produced remains
very low compared with the
maximum concentration attain-
able. In a number of the ex-
periments referred to below,
the concentration of ozone did
not exceed one per cent of the
maximum. A number of dif-
ferent forms of apparatus with
a point electrode were used by
Warburg in determining these
yields. In the apparatus shown
in Figure 128, E, the earth
electrode, is a platinum plate ;
in Figure 129 E is a platinum
cylinder ; and in Figure 130,
consisting of a liter bottle, E is
concentrated sulphuric acid.
Figure 131 shows an ozonizer
with a number of point elec-
FIG. 130. Experimental ozoiiizer
With the point negative, for
a given current strength the yield per coulomb is independent
Warburg and Leithauser, Ann. der Phys. 28, 25, (1909).
THE PRODUCTION OF OZONE
of the voltage, as shown by the results of Table 43, 1 obtained
with oxygen 93 per cent pure by volume. In the following
tables the current given is for one point only, in case the appa-
ratus contained more than one point.
AMPERES x 10
GRAMS OZONE PER COULOMB
FIG. 131. Experimental ozonizer
The yield is also independent of the form of the anode, and
decreases slowly with increasing current, as is shown by the
following results obtained with different forms of anode : l
Warburg, Ann. der Phys. 13, 472, (1904).
APPARATUS IN FIG. 128
APPARATUS IN FIG. 129
Amperes x 10 6
Grams Ozone per
Amperes x 10 6
Grams Ozone per
These results are for the case where negative light appears
only on the point. If it appears at other parts of the electrode,
the yield may increase with the current. The yield depends
further on whether the points have been previously used, being
greater for previously used points : 2
Oxygen, 96 per cent pure, by volume
TIME DURING WHICH
OZONIZER WAS USED
AMPERES x 10 6
GRAMS OZONE PER
This increase in the yield is accompanied by a change in the
character of the light on the electrode. When the final state
of the electrode has been reached the yield decreases for increas-
ing current to a certain point, as shown by the results in Table
46 of experiments with 98.5 per cent oxygen : 3
2 Warburg, Ann. d. Phys. 17, 6, (1905),
* Warburg, Ann. d. Phys. 17, 6, (1905).
THE PRODUCTION OF OZONE
GRAMS OZONE PER
GRAMS OZONE PER
AMPEBES x 106
If the current is increased to a still higher value, the yield
reaches a minimum and then increases with the current. This
is shown by the results in Table 47, obtained with new points
and with oxygen 96 per cent pure by volume : 4
AMPERES x 10 6
GRAMS OZONE PER
In this case also a marked change in the appearance of the
light accompanies the increase in the yield after passing the
minimum. After a certain amount of practice, it is even pos-
sible to predict from the appearance of the light what the yield
will be. 6
In changing the temperature and pressure of the gas, not only
the substance which is to be acted upon is altered, but also
the agent which brings about the reaction ; for the light changes
its character when the physical state of the gas through which
the current is passed is altered. This fact complicates the
study of this subject. The results in Table 48 with oxygen
98.5 per cent pure by volume show how the yield increases
with the pressure : 6
4 Ann. d. Phys. 17, 10, (1905). 6 Ann. d. Phys. 17, 7, (1905).
e Ann. d. Phys. 17, 12, (1905).
PRESSURE IN MM.
GRAMS OZONE PER
Points previously sub-
jected to long use. Current
= 37.4 x 10~ 6 ampere
Fresh points. Current
= 17.5 x 10~ 6 ampere
Between 780 and 460 millimeters pressure, the yield A p for any
pressure p is given by the equation 7
A p = A 7QO [1 - (760 -p) 0.00089].
The temperature of the gas in all of these experiments lay
between 17 and 23. Table 49 shows the effect on the yield
of changing the temperature :
Oxygen 98.5 per cent pure by Volume. Current 37.4 X 10~ 6 Ampere
MM. OP MERCURY
GRAMS OZONE PER
This decrease in the yield is largely due to the decrease in the
density of the oxygen when the temperature is raised. If the
pressure is increased enough to keep the density constant,
the yield is very little affected. This is shown in Table 50,
obtained with points not previously used :
7 Ann. d. Phys. 28, 21, (1909).
THE PRODUCTION OF OZONE
PRESSURE IN MM.
AMPERES x 10 6
GRAMS OZONE PER
It is therefore evident that if the density is constant, the yield
is changed only a few per cent between 10 and 80 degrees.
The relation between the yield per coulomb and the concen-
tration of the ozone produced from 98 per cent oxygen is linear. 8
If the concentration is allowed to reach 12.9 grams per cubic
meter, the yield falls to 75 per cent of its value for a concentra-
tion of 1.3 to 1.6 grams per cubic meter. The formula
^ = 0.166- 0.00215 c
gives the yield per coulomb for different values of the concen-
tration c between 1.6 and 12.9 grams per cubic meter, and for
a current of 0.0175 x 10~ 3 ampere. The yield per kilowatt
hour is given by the equation :
B = 71.0 - 1.58 c + 0.00090 c 2 .
These results were obtained with spheres, in place of points, 1.5
to 2 millimeters in diameter, melted on a wire 1 millimeter in
diameter. The yield for this kind of electrode is much higher
than for points, and when used as the positive pole, spheres do
not show the aging effect that is observed with points.
The presence of water vapor in oxygen reduces the yield
nearly proportionally to the pressure of the water vapor. 9
The reduction in the yield for seven millimeters pressure is
s Warburg and Leithauser, Ann. d. Phys. 20, 734, (1906).
9 Ann. d. Phys. 20, 751, (1906).
about 94 per cent of its value for dry oxygen. There is also
a great tendency for the formation of sparks when the gas is
When oxygen is mixed with only 7 per cent of nitrogen, the
silent discharge produces no oxide of nitrogen, 10 but when air
is used oxides of nitrogen are produced. The spark discharge
produces only oxides, and these prevent the formation of
ozone. 11 For air, the yield per coulomb is independent of the
voltage for a constant current, as in the case of oxygen, but it
is much smaller than for oxygen. This is shown in Table 51. M
Air. Temperature 20. Six Points. Current for One Point = 21.9 X 10-6 ampere
POINT AND PLATE IN
GRAMS OZONE PER
For air, the yield first decreases with increasing current and
reaches a minimum, after which it increases more rapidly than
for oxygen, as shown in Table 52.
AMPERES x 10 6
POINT AND PLATE IN
GRAMS OZONE PER
10 Warburg, Ann. d. Phys. 13, 470, (1904).
11 Warburg and Leithauser, Ann. d. Phys. 20, 743, (1906).
12 Warburg, Ann. d. Phys. 17, 25, (1905).
THE PRODUCTION OF OZONE 305
The change that takes place in the luminosity when the yield
begins to increase is similar to that in the case of oxygen.
The effect of the concentration of the ozone produced on the
yield in air is approximately the same as in oxygen. 13 A, the
yield in grams per coulomb, and B, the yield in grams per kilo-
watt hour, are given by the following equations, for values of
the concentration c between 2.19 and 9.62 grams per cubic
A = 0.0780 - 0.00220 c,
B = 42.6 - 1.60 c + 0.0036 c 2 .
The effect of moisture is greater for air than for oxygen, 7
millimeters pressure of water vapor reducing the yield to 69. 7
per cent of its value for dry air. 14
The effect of temperature on the yield for negative points
in air has not been determined.
Yield per Coulomb for Positive Point Electrode
The effect of increasing the current on a positive point
electrode is quite different from the effect on a negative point.
With positive points the yield is smallest for small currents,
but increases as soon as the positive brush appears, and, with
points not previously used, it finally reaches values exceeding
the highest ones obtainable with negative points. This is
shown in Table 53. l The yield is very much affected by the
character of the positive brush, which depends on a number of
circumstances difficult to control.
The effects of temperature and pressure on the yield with
positive points in oxygen have not been investigated.
The relation between the yield in grams per coulomb, A, and
the concentration of ozone, <?, produced, is given by the equa-
-4 = 0.166- 0.00853 c,
13 Warburg and Leithauser, Ann. d. Phys. 20, 734, (1906).
" Ann. d. Phys. 20, 734, (1906).
i Warburg, Ann. d. Phys. 17, 19, (1905).
which holds for values of c between 1.18 and 8.49 grams per
cubic meter. 2 The corresponding equation for grams per
kilowatt hour is
=67.0- 3.44 c.
These results are for spheres in place of points, and for a
current on one sphere of 0.033 x 10~ 3 ampere.
93 per cent Oxygen by Volume
WIRE OF + POLE
98.5 per cent Oxygen
The reduction in the yield by water vapor is much greater
for positive points in oxygen than for negative. When the
vapor pressure of the water is seven millimeters, the yield is
only 64 per cent of its value for dry oxygen. 3
Positive points in air act similarly to positive points in
oxygen, except that the positive brush is more capricious in
air. 4 The yield is much smaller than for negative points as
long as no positive brush appears, and while the positive glow
covers the point in a thin layer; but with the appearance of
a Warburg and Leithauser, Ann. d. Phys. 20, 739, (1906).
3 Ann. d. Phys. 20, 753, (1906).
* Warburg, Ann. d. Phys. 17, 26, (1905).
THE PRODUCTION OF OZONE
the positive brush the yield increases and reaches values much
higher than any obtained with negative points in air. This
will be seen from the results of Table 54.
Atmospheric Air. Positive Points of wire 0.25 mm. in Diameter
POINT AND PLATE
AMPERES x 10 6
Per Kilowatt Hour
25.4"! Voltage near
26.1 [ sparking
16.8 J point
The yield in grams per coulomb, A, and in grams per
kilowatt hour, J9, in air are given by the equations:
.4 = 0.114- 0.008670,
B = 60 - 6 e
for values of c between 0.58 and 3.94 grams per cubic
The effect of water vapor on the yield with positive points in
air is the greatest of any so far considered. In this case, for a
pressure of water vapor of 7 millimeters, the yield falls to
49.1 per cent of its value for dry air.
It is evident, from the fact that positive points near the
sparking potential give a better yield than negative points,
both for oxygen and for air, that if an alternating current is
used the yield will not be as good as with a direct current with
positive points, for with an alternating current the points will
be negative half of the time. This has been tested by direct
comparison for oxygen and air. The results are given in
Table 55. 6
6 Warburg, Ann. d. Phys. 17. 29, (1905),
98.5 per cent Oxygen. Temperature 19
AMPERES x 10
PLATE IN MM.
The Yield per Kilowatt Hour for Positive and for
It is evident from what has preceded that the yield per unit
of energy depends on a large number of factors. For negative
points, it is best to use the smallest possible current and a short
distance between the points and the plate, and the points should
not be fresh. For positive points, heavy, new wires one milli-
meter thick are best, and the potential should be as high as
possible without producing sparks. The distance between
point and plate should not be too great, for though the yield
per coulomb increases, the yield per kilowatt hour decreases, as
seen in Table 54.
Much better yields both for positive and for negative points
are obtained by substituting small spheres 1.5 to 2 millimeters
in diameter for the points, as is seen in the results on the effect
of concentration on the yield of ozone. It can be calculated
from the equations given above, that for air, concentrations up
to 4 grams per cubic meter are produced most economically
THE PRODUCTION OF OZONE 309
when the points are positive and the current high, while con-
centrations between 4 and 9 grams per cubic meter are most
economically produced with negative points and low currents. 1
About 30 grains per kilowatt hour can be obtained in the latter
case for a concentration of 8 to 9 grams per cubic meter.
Theory of Ozone Formation by the Silent Discharge
That the formation of ozone is not electrolytic in its nature 1
can be shown from the yields given above, which vary between
0.003 and 0.1 gram per coulomb. Since one equivalent of
hydrogen reduces 24 grams of ozone, 24 may be taken as the
latter's equivalent weight. The number of coulombs required
to produce 24 grams of ozone therefore lies between 8000 and
240, numbers not at all comparable with the electrochemical
equivalent, 96,540 coulombs. On the other hand, the energy
required is considerably greater than the heat of the reaction.
On the basis of the highest yield of 70 grams per kilowatt hour
(see the equation for yield with negative points in oxygen), the
energy required for one mole of ozone is 589,000 calories, 20
times as much as the heat of the reaction. Warburg's theory
is that ozone is formed by those electrons that have a velocity as
high as that required for the production of luminosity. Ozone
may be formed directly by the impact of such electrons with
oxygen molecules or by the intermediate production of short
ether waves. 2
The Siemens Ozonizer l
The effect of pressure is the same in a Siemens ozonizer as
for a point and plate, both being represented by the formula
given above :
A = Aeo[l -(760-^)0.00089].
1 Warburg and Leithauser, Ann. d. Phys. 20, 742, (1906).
1 Warburg, Ann. d. Phys. 13, 474, (1904).
2 Warburg, Ann. d. Phys. 17, 7, (1905).
1 Warburg and Leithauser, Ann. d. Phys. 28, 17, (1909). The following dis-
cussion is taken from this article, except where other references are given.
In air the pressure of oxygen is 160 millimeters, and in 96 per
cent oxygen, 730 millimeters. Substituting these values in the
This relation is verified by the following results, in which the
gas was passed through the ozonizer at such a rate that the
concentration remained low. The effective current was meas-
GRAMS OZONE PER COULOMB
50 alternations per
second. Apparatus : 2
concentric glass tubes
Central tube is bare
The quantity of ozone produced per coulomb for a given
apparatus increases with the potential as in the case of positive
points, and the effect of water vapor is to lower the yield. 2
A factor not considered in Warburg's work, but one which
has a great effect on the yield, is the transparency of the glass
of the ozonizer for ultra-violet light. 3 An ozonizer of quartz,
for example, which is transparent to ultra-violet rays, gives
only half as much ozone, other conditions being equal, as a
glass ozonizer of the same dimensions.
The relation between the yield and the concentration of the
ozone leaving the ozonizer is similar to that for points, and is
given in Table 57.
The formation of ozone is proportional to the mean current,
idt, and not to the effective current,
2 A. W. Gray, Phys. Rev. 19, 362, (1904).
F. Russ, Z. f. Elektroch. 12, 409, (1906).
THE PRODUCTION OF OZONE
given by measuring instruments ; consequently, if the effective
current is measured, the yield will also depend on the wave
form of the current.
Oxygen 96 per cent pure. Maximum Concentration of Ozone equals 168 Grams
per cubic meter
CONC. OZONE IN GKAMS
PER CUBIC METER
GRAMS OZONE PER
CONC. OZONE IN GRAMS
PEE CUBIC METER
GRAMS OZONE PER
The effect of temperature is similar to that in the apparatus
with point and plate electrodes : the yield for zero concentra-
tion changes very little, while the deozonizing effect of the
current on the ozone already formed increases with the temper-
The yield per kilowatt hour is greater where one electrode is
not covered with an insulator, because of the greater current
for a given voltage and the greater value of cos <f>. The thick-
ness of the dielectric has no effect. 4 The following table gives
the yield obtained by Warburg and Leithauser in grams ozone
per kilowatt hour. 5
GRAMS PER KILOWATT-
PLATES IN MM.
AMPERES PER SQUARE
Cone. = 10
4 See also Ewell, Phys. Rev. 22, 243, (1906).
6 Ann. d. Phys. 28, 36, (1909).
It will be noticed that the yield for a Siemens ozonizer is
considerably higher than for those having a point and a plate
electrode, for which the highest value was 36 grams per kilo-
watt at a concentration of 4 grams per cubic meter.
2. THE TECHNICAL PRODUCTION OF OZONE
Ozone is produced commercially for the purification of water,
for bleaching, and for use as an oxidizing agent in organic
chemistry. 1 In water pu-
rification, the action of
ozone is to oxidize the
organic matter and to
Siemens and Halske
make the ozone apparatus
shown in Figure 132. 2
The discharge chamber is
between two concentric
metal cylinders, between
FIG. 132. The Siemens and Halske ozonizer
which 8000 volts alternating are applied. The cylinders are
FIG. 133. The Tindal ozonizer
immersed in water for cooling, and the outer one is connected
to earth. One of the surfaces from which the discharge takes
1 J. W. Swan, Z. f. Elektroch. 7, 950, (1901).
2 Z. f. Elektroch. 10, 13, (1904); Electrochem. Ind. 2, 67, (1904).
THE PRODUCTION OF OZONE
place is covered with a glass dielectric. Air enters at the top,
is partly changed to ozone in passing between the walls of the
concentric cylinders, and leaves the apparatus from below.
The concentration of the ozone is about 2 grams per cubic
meter, which is high enough for all ordinary purposes. The
yield varies between 18 and 37 grams per kilowatt hour. 3
The Tindal ozonizer is
shown in Figure 133.
It is in the form of a
box, the inner walls of
which are water-cooled
electrodes and are con-
nected to earth. The
other electrodes are metal
plates inside the box and
insulated from it. Be-
tween 40,000 and 50,000
volts are applied to the
rnier 2 apparatus is shown in Figure 134. It consists of a num-
ber of cylindrical, parallel, hollow electrodes of about a square
meter area, covered with glass and mounted in a box. Water cir-
for cooling, be-
volts are ap-
apparatus 4 is
FIG. 134. The Abraham-Marmier ozonizer
The Otto ozonizer
FIG. 135. Longitudinal-vertical FIG. 136. Transverse
section vertical section , . ,,,.
shown in r ig-
ures 135 and 136. It consists of a chamber, K, the metal wall,
EV of which forms one electrode. The sheet steel rings, $,
Askenasy, Elektrochemie, 1, 246, (1910).
* Z. f. Elektroch. 7, 790, (1901).
sharpened at M, and mounted on an axle on which they rotate,
are the other electrode, E%. There is no solid dielectric. Air
passes in the box at B arid comes .out at A. While in the box
it is ozonized and thoroughly mixed by the rotating electrode.
If an arc were to form between the electrodes, it would be ex-
tinguished as the grooves RR in the
rotating electrode pass the insulat-
ing base of the box, aa. About 25,000
volts are applied to the electrodes,
the distance between which may be
from 10 to 100 millimeters.
Small ozonizers are now made for
sterilizing water where it is drawn
for use, as shown in Figure 137. 5
The transformer and ozonizer are in
a metal case, 0. P and S are respec-
tively the primary and the secondary
of the transformer. The primary is
supplied with 100 to 250 volts, which
is transformed to 15,000 volts in the
secondary. The ozonizer consists of
six or more glass plates, 6r, supported
on a grooved bracket at the bottom,
and by grooved slips at the sides and
top. Three pairs of plates, each plate
covered on one side with tin foil, are
shown in the sketch. The discharge
takes place between two opposite
FIG. 137. Small ozonizer con- sheets of tin foil one millimeter apart,
without an intervening dielectric.
The air enters the space between the plates at the top and
sides, and is sucked down through the opening at the bottom
of the ozonizer by the action of the water at B. The water
carries the ozone to .A, where mixture and sterilization take
place. The current in the transformer is of course turned on
only when water is drawn.
5 Electrochem. and Met. Ind. 6, 304, (1908>
TABLE OF ATOMIC WEIGHTS
O = 16.00
. . Al
. . He
. . H
. ". A
. . In
. . As
. . I
. . Ba
. . Ir
Bismuth. . . .
. . Bi
. . Fe
. . B
. . Kr
Bromine . .
. . Br
Lanthanum . .
. . La
. . Pb
. . Cs
. . Li
. . Ca
. . Lu
. . C
Magnesium . .
. . Ce
Manganese . .
. . Mn
M^ercury . . *
. . Cr
. . Mo
. . Co
Neodymium . .
. . Nd
. . Cb
. . Ne
. . Cu
Nickel. . . .
. . Ni
Dysprosium . .
. . N
. . Er
. . Os
. . O
. . Fl
. . Pd
Gadolinium . .
. . Gd
Phosphorus . .
Platinum * .
. . P
. . Pt
Germanium . .
. . Ge
. . Gl
Potassium . .
. . K
. . Pr
. . Au
. . Rd
1 International Committee on Atomic Weights, J. Am. Chem. Soc. 32, 3, (1910).
TABLE OF ATOMIC WEIGHTS Continued
. . . . Rh
. . . . Tl
. . . . Rb
. . . . Th
. . . . Sm
Tin . . .
. . . . Sn
. . . . Sc
. . . . Ti
. . . . Se
. . . . W
Silver . .
. . . . Na,
. . . . Xe
. . . . Sr
. . . . Yb
. . . . S
. . . . Y
. . . . Ta
. . . . Te
. . . . Zr
. . . . Tb
TABLE OF ELECTROCHEMICAL EQUIVALENTS OF THE MORE
IMPORTANT ELEMENTS 1
DEPOSITED BY 1
AMPERE IN 1 SECOND
BY 1 AMPERE IN
. . . Al
. . . Sb
. . . Ba
. . . Bi
. . . Br
. . . Cd
. . . Ca
. . . Ce
. . . Cl
. . . Cr
. . . Cu
1 Based on the atomic weights of 1910 and on the value 96,540 for the electro-
TABLE OF ELECTROCHEMICAL EQUIVALENTS Continued
DEPOSITED BY 1
AMPERE IN 1 SECOND
BY 1 AMPERE IN
Copper Cu 2
Fluorine Fl 1
Gold Au 1
" " 3
Hydrogen H 1
Iodine I 1
Iron Fe 2
Lead Pb 2
Lithium Li 1
Magnesium . . . . . Mg 2
Manganese Mn 2
" " 3
Mercury Hg 1
Nickel Ni 2
Oxygen O 2
Potassium K 1
Silver Ag 1
Sodium Na 1
Tin Sn 4
Titanium Ti 4
Zinc . . Zn 2
NUMERICAL RELATION BETWEEN VARIOUS UNITS
ENGLISH AND METRIC MEASURES
NOTE. Values taken from "Tables of Weights and Measures," U. S. Coast
and Geodetic Survey, 1890.
1 meter = 39.37 inches (legalized ratio for the U. S.)
1 meter = 1.093611 yard
1 meter = 3.280833 feet
1 kilometer = 0.621370 mile
1 inch = 25.40005 millimeters
1 foot = 0.304801 meter
1 yard = 0.914402 meter
1 mile = 1.609347 kilometer
1 kilogram = 2.204622 pounds av.
1 grain = 15.43235639 grains
1 pound =0.4535924277 kilograms
1 ounce av. = 28.34853 grams
1 ounce troy = 31.10348 grams
1 metric ton = 1000 kilograms
1 liter = 1.05668 quarts
1 liter = 0.26417 U. S. gallon
1 liter = 33.814 U. S. fluid ounces
1 quart, U. S. = 0.94636 liter
1 gallon, U. S. = 3.78544 liters
1 fluid ounce = 0.029573 liter
MECHANICAL EQUIVALENT OF HEAT
1 kilogram-calorie (1 kilogram water raised 1 C. at 15 C.) = 427.3
kilogrammeters (at sea level, latitude 45, g = 980.6 c.g.s.)
1 British thermal unit (1 pound of water raised 1 F. at 59 F.) = 778.8
foot pounds at sea level, latitude 45
1 gram-calorie (1 gm. of water raised 1 C. at 15 C.)= 4.190 x 10 7 ergs
1 joule = 10 7 ergs
= 0.2387 gram-calorie
[Winkelmann, Handbuch der Physik, 1, 79, (1908)]
1 kilowatt = 1000 watts
1 horse power (HP) = 550 foot pounds per second
= 746 watts
= 0.746 kilowatt
1 kilowatt = 1.34 horse power
The metric horse power, called in German Pferdekraft or Pferde-
= 75 kilogrammeters per second
= 736 watts
Therefore 1 English horse power = 1.014 metric horse power.
LEGAL ELECTRICAL UNITS 1
The legal electrical units in the United States are defined as
(1) The unit of resistance is the international ohm, represented
by the resistance offered to a steady current by a column of mercury
at C. whose mass is 0.4521 gram, of a constant cross section, and
whose length is 106.3 centimeters.
(2) The unit of current is the international ampere and is the
equivalent of the unvarying current, which, when passed through
a solution of silver nitrate in water, in accordance with standard
specifications, deposits silver at the rate of 0.001118 gram per
The specifications for the practical application of this definition
are the following:
In employing the silver voltameter to measure currents of about
1 ampere, the following arrangements shall be adopted :
The cathode on which the silver is to be deposited shall take the
form of a platinum bowl not less than 10 centimeters in diameter
and from 4 to 5 centimeters in depth.
The anode shall be a disk or plate of pure silver some 30 square
centimeters in area and 2 or 3 millimeters in thickness.
This shall be supported horizontally in the liquid near the top of
the solution by a silver rod riveted through its center. To prevent
the disintegrated silver which is formed on the anode from falling
upon the cathode, the anode shall be wrapped around with pure filter
paper, secured at the back by suitable folding.
The liquid shall consist of a neutral solution of pure silver nitrate,
containing about 15 parts by weight of the nitrate to 85 parts of
The resistance of the voltameter changes somewhat as the current
passes. To prevent these changes having too great an effect on the
current, some resistance besides that of the voltameter should be
inserted in the circuit. The total metallic resistance of the circuit
should not be less than 10 ohms.
Method of Making a Measurement. The platinum bowl is to be
washed consecutively with nitric acid, distilled water, and absolute
1 Bulletin of U. S. Coast and Geodetic Survey, Dec. 27, 1893.
alcohol ; it is then to be dried at 160 C., and left to cool in a desic-
cator. When thoroughly cool it is to be weighed carefully.
It is to be nearly filled with the solution and connected to the rest
of the circuit by being placed on a clean insulated copper support to
which a binding screw is attached.
The anode is then to be immersed in the solution so as to be well
covered by it and supported in that position ; the connections to the
rest of the circuit are then to be made.
Contact is to be made at the key, noting the time. The current is
to be allowed to pass for not less than half an hour, and the time of
breaking contact observed.
The solution is now to be removed from the bowl and the deposit
washed with distilled water and left to soak for at least six hours.
It is then to be rinsed successively with distilled water and absolute
alcohol and dried in a hot-air bath at a temperature of about 160 C.
After cooling in a desiccator it is to be weighed again. The gain in
mass gives the silver deposited.
To find the time average of the current in amperes, this mass,
expressed in grams, must be divided by the number of seconds
during which the current has passed and by 0.001118.
In determining the constant of an instrument by this method the
current should be kept as nearly uniform as possible and the readings of
the instrument observed at frequent intervals of time. These obser-
vations give a curve from which the reading corresponding to the mean
current (time average of the current) can be found. The current, as
calculated from the voltameter results, corresponds to this reading.
The current used in this experiment must be obtained from a bat-
tery and not from a dynamo, especially when the instrument to be
calibrated is an electrodynamometer.
(3) The unit of electromotive force is the international volt,
which is the electromotive force that, steadily applied to a conductor
whose resistance is one international ohm, will produce a current of
an international ampere, and is practically equivalent to ^ of the
electromotive force of a Clark cell, at 15 C., when prepared accord-
ing to the standard specifications. 1
(4) The unit of quantity is the international coulomb, which is
the quantity of electricity transferred by a current of one interna-
tional ampere in one second.
1 See Bulletin of U. S. Coast and Geodetic Survey, Dec. 27, 1893.
(5) The unit of work is the joule, equal to 10 6 (see under Mech.
Equiv. of Heat) ergs, and is practically equivalent to the energy
expended in one second by an international ampere in an inter-
(6) The unit of power is the watt, and is practically equivalent
to the work done at the rate of one joule per second.
ABRAHAM and Marmier, 313.
Acheson, 210, 217, 219, 220, 221.
Addicks, 47, 48, 53, 54.
Adolph, 104, 105.
Betts, 64, 236.
Birkeland, 279, 282, 287.
Bodenstein and Katayama, 275.
Borchers, 57, 75.
Bradley, 230, 276.
Bredig, 11, 266, 267.
Bunsen, 6, 143, 228, 236.
Burgess, 36, 146.
Castner, 131, 233.
Colson, 209, 217, 218.
Cowles, 185, 209, 229.
Davy, E., 202.
Davy, H., 228, 233, 236.
Despretz, 208, 220.
Donath and Frenzel, 276.
Easter brooks, 51.
Edison, 173, 182.
Elbs, 7, 77, 171.
Engelhardt, 117, 118, 122, 141.
Erlwein, 64, 266, 268.
Eyde, 281, 282.
Finckh, 271, 272.
Fischer, A., 21, 25, 27, 29.
Fischer, F., 289, 291.
FitzGerald, 192, 200, 209, 211, 219, 220,
Foerster, 6, 24, 37, 45, 50, 55, 62, 67, 72,
78, 79, 81, 82, 85, 88, 91-95, 97, 98,
101-103, 109, 110, 112, 115, 116, 178,
181, 183, 266.
Frank, 266, 268, 287.
Fromm, 45, 46.
Gall and Montlaur, 123.
Garuti and Pompili, 140.
Gibbs, Walcott, 21, 22.
Gibbs, W. T., 123.
Gladstone, 157, 158.
Goodwin, H. M., 14, 23.
Goodwin, J. H., 237.
Giinther, 45, 67.
Gyr, 115, 116.
Haas, 120, 122.
Haber, 36, 38, 55, 74, 206, 225, 271, 273,
278, 285, 287.
Hargreaves and Bird, 126.
Hasse, 46, 67.
Heimrod, 2, 3.
Hering, 187, 192, 198, 261.
Heroult, 230, 247, 249, 256.
Hoepfner, 44, 47.
Holland, 173, 177.
Jacoby, H., 266.
Jacoby, M. H., 39.
Jahn, S., 288, 290.
Joly, J., 11.
Jorre, 82, 101; 103.
Kellner, 118, 121.
Kennelly, 173, 184, 204.
Kershaw, 47, 123, 125, 243.
Kiliani, 46, 49.
Kjellin, 259, 262.
Koenig, 273, 274.
Kohlrausch, F., 8, 15.
Kohlrausch, W., 158.
Langbein, 30, 35.
Le Blanc, 1, 22, 23, 25, 26, 69, 75, 76, 107,
109, 159, 161, 267, 272.
Le Chatelier, 191.
Leithauser, 273, 292-311.
Le Rossignol, 286.
Lewes, 202, 206, 207.
Lewis, 15, 74.
Liebenow, 161, 163.
Lorenz, 94, 109, 233.
Lyon, 251, 252.
Magnus, 52, 54.
Marchese, 43, 44.
Moissan, 202, 209, 216, 220, 266.
Miiller, E., 74, 81, 85, 89, 91-94, 97, 108-
110, 112, 117.
Muller, F. C. G., 10.
Mylius, 45, 46.
Nernst, 1, 71, 74, 148, 271.
Nicholson and Carlisle, 6.
Oettel, 4, 86, 92, 122.
Ostwald, 13, 150.
Richards, H. C., 195.
Richards, J. W., 123, 132, 204, 222, 277.
Richards, T. W., 1, 15, 22.
Rochling and Rodenhauser, 262.
Schoop, 141, 181.
Schuckert, 119, 122.
Schiitzenberger, 209, 217, 218.
Seward and von Kugelgen, 238.
Siemens Brothers, 141.
Siemens and Halske, 44, 312.
Stassano, 243, 254.
Thompson, 51, 202, 203, 232, 267.
Tribe, 157, 158.
Tucker, 203, 217, 220.
Ulke, 51, 54, 55.
Walker, 117, 121.
Warburg, 273, 290-311.
Whiting, J., 133.
Whiting, S. E., 173, 184.
Wohler, F., 202, 226, 228.
Wohler, P., 237.
Wohlwill, 50, 57, 58, 61, 112.
Alkali hydrate and chlorine ; diaphragm
process, 101-104; bell process, 104;
mercury cathode process, 106 ; mer-
cury diaphragm process, 107 ; bell cell,
131 ; Castner cell, 135 ; Hargreaves-Bird
cell, 127 ; McDonald cell, 126 ; Town-
send cell, 129; Whiting cell, 133-136.
Aluminum, first isolated, 228 ; reduction
of oxide by carbon, 229 ; Hall's process,
229-230; Bradley's process, 230;
Heroult's process, 230 ; furnace for
electrolytic production, 231 ; yield per
horse power day, 231 ; temperature of
bath, 231 ; table of production, 232 ;
electrolytic production as laboratory
Alundum, 227 ; table of production, 228.
Bell alkali chlorine cell, 131.
Brass plating, 37.
Bright dipping bath, 31.
Bromate, electrolytic production of, 115.
Bromoform, electrolytic production of,
Calcium, first isolated, 236 ; electrolytic
production by Rathenau, 237 ; by
Seward and von Kiigelgen, 238 ; by P.
Calcium carbide, discovery, 202 ; heat of
formation, 202 ; equilibrium with
carbon monoxide, 202 ; chemical
properties, 203 ; Willson's original
furnace for manufacture of, 204 ;
first furnace at Niagara Falls, 205 ;
Horry furnace, 206 ; yield per kilowatt
day, 207 ; raw materials for, 207 ;
table of production, 206.
Calcium cyanamide, discovery of produc-
tion from carbide, 266 ; pressure of
nitrogen in, 267 ; chemical behavior,
268; manufacture, 269.
Carbon, different forms distinguished,
Carbon bisulphide, electrothermic pro-
Carbon electrodes, thermal and elec-
trical conductivities of, 198-199 ;
porosity, 95-96 ; as anodes in alkali
chloride electrolysis, 95-97, 105.
Carborundum, first produced, 208 ; dis-
covery by Acheson, 210 ; named, 210 ;
furnace at Niagara Falls for production
of, 212 ; reaction of formation, 212 ;
raw materials for, 214 ; yield per kilo-
watt hour, 214 ; table of production,
215 ; uses, 215 ; analysis of, 210, 216 ;
temperature of formation and of de-
composition, 217 ; chemical properties,
Carborundum fire sand, 211.
Chlorate, production by electrolytic dis-
charge of hypochlorite, 85 ; current effi-
ciency when so formed, 90 ; electro-
lytic production in acid solution, 92 ;
in alkaline solution, 84, 93 ; current
and energy yields, 98 ; Gall and Mont-
laur cell for production of, 123 ; Gibbs
cell, 123; Lederlin and Corbin cell,
Chlorine, chemical action on hydrate,
80-84 ; electrolytic production, see
Chloroform, electrolytic production of,
Complex salts in electroanalysis, 25, 28.
Conductivity measurement as method of
chemical analysis, 15-16.
Conductivity, thermal ; method of de-
termining for carbon electrodes, 197 ;
table of values for refractories, 191.
Copper, refining, object of, 47 ; electro-
lytic method, 48 ; composition of
anodes, 48, 49 ; composition of cathodes,
49 ; composition of slime, 50 ; com-
position of fresh electrolyte, 51 ; of
foul electrolyte, 52 ; behavior of im-
purities in anodes, 49 ; circulation of
electrolyte, 52 ; size of tanks, 52-54 ;
multiple and series systems of connec-
tions, 53 ; effect of temperature on
power required, 54 ; voltage per tank,
54 ; polarization, 54 ; cost, 54.
Copper, winning of, 43-45.
Copper plating, 35.
Coulometers, silver, 2-4 ; copper, 4-6
water, 6-11; silver titration, 11-12.
Diaphragms, construction of, 75.
Edison storage battery, history and con-
struction, 173-177 ; table of different
sizes, 177 ; theory of, 178-184 ; nickel
electrode, composition of, 178 ; po-
tential of, 179 ; efficiency of charging
181 ; iron electrode, potential of, 182
effect of mercury contained, 182 ;
chemical changes in battery, 183 ; elec-
tromotive force of, 184 ; capacity, 184 ;
Electric furnace, classification, 186 ;
design, 192, 199, 200; heat loss
through walls, 187 ; through elec-
Electrochemical analysis, by potential
measurement, 13-15 ; by conductiv-
ity measurement, 15-16 ; by titration,
with a galvanometer as indicator, 17-
20; by electrolytic deposition, 20-
29 ; change in potential at cathode
Electrochemical equivalent, 1.
Electrode voltage, 196.
Electrolytic bleaching solution, see Hy-
Electromotive series, 22.
Electroplating, 30-34 ; by contact, 34 ;
by dipping, 34.
Faraday's laws, 1.
Fluoride, electrolysis of, 113.
Foil, metallic, electrolytic production of,
Galvanometer as indicator in titrations,
Gas analysis as a means of determining
yield of hypochlorite, 86-87.
Gold plating, 38.
Gold refining, 61-64; cyanide process
for extracting from ore, 63.
Graphite, first made artificially, 220;
theory of formation, 221 ; furnace for,
222 ; table of production, 224 ; thermal
and electrical conductivities of, 198-
199 ; electrodes, see Carbon.
Hydrogen, electrolytic production of,
137-141; Schmidt cell, 137; Garuti
and Pompili cell, 140 ; Schoop cell, 141 ;
Siemens Brothers and Obach cell, 141.
Hydrogen electrode, in electroanalysis
Hypochlorite, production by action of
chlorine on hydrate, 80-84; by elec-
trolysis of alkali chloride solution on
smooth platinum electrodes, 84-94;
effect of temperature, 88; effect of
current density, 89 ; prevention of re-
duction by chromate, 89; effect of
alkalinity on electrolytic production,
93 ; effect of temperature on production
in alkaline solution, 94 ; decomposition
point of, 109 ; production with platin-
ized anode, 94 ; with carbon anode,
95 ; effect of concentration of chloride
solution on yield, 89, 96 ; maximum
concentration attainable, 98 ; current
and energy yields, 98 ; Hermite cell for
electrolytic production of, 117; Kell-
ner cell, 118, 121 ; Haas and Oettel
cell, 120, 122; Schuckert cell, 119,
Hypoiodite, 115; electrolytic discharge
lodate, 115, 116.
lodoform, electrolytic production of, 77.
Iron, metallurgy of, 239-242; electro-
thermic reduction from ores, 242 ;
Stassano's preliminary experiments on,
244; Keller furnace for, 246; He-
roult's experiments on, 247-249 ; fur-
nace of Gronwall, Lindblad, and Stal-
shane, 249 ; furnace at H6roult, Cali-
Lead refining, 64-67.
Mercury cathode in electroanalysis, 22.
Multiple system of connections in metal
Nickel plating, 34.
Nickel refining, 55-57; Orford process,
Nitrogen, fixation of ; by carbide, 266 ;
pressure of, in calcium cyanamide, 267;
yield of calcium cyanamide per unit of
power, 269, 287 ; by oxidation by elec-
tric discharge, discovered, 270 ; ther-
mal equilibrium in, 271 ; electrical
equilibrium, 274; velocity of oxida-
tion, 272 ; yield per unit of power, 276,
287 ; apparatus of Bradley and Love-
joy for, 276, 277; of Birkeland and
Eyde, 279-282 ; of Schonherr and Hess-
berger, 282-283 ; of H. and G. Pauling,
283-285 ; by direct union with hydro-
gen, 285 ; equilibrium, 286, 287.
Overvoltage, in electroanalysis, 24 ; in
lead storage battery, 170 ; in reduction,
71 ; in oxidation, 73.
Oxidation, electrolytic, 73 ; catalytic
effect of anode on, 74 ; of chromium
sulphate, 74 ; of attackable anodes,
Oxygen, electrolytic production of, see
Ozone, discovery, 288 ; heat of formation,
288 ; free energy of, 289 ; velocity of
formation by silent electric discharge,
290 ; yields by different methods of
production, 291 ; maximum concen-
tration by silent discharge, 294-296 ;
yield per coulomb, for negative points,
298-305 ; effect of temperature, 302 ;
of pressure, 303 ; of concentration of
ozone produced, 303 ; of water vapor,
303; of current strength; yield per
coulomb for positive points, 305-308 ;
effect of current strength, 305 ; of
temperature, 305 ; of concentration of
ozone produced, 305 ; of water vapor,
306 ; yield with alternating current,
307 ; yield per kilowatt hour for posi-
tive and for negative points, 308 ;
theory of formation, 309 ; effect of
transparency of glass ofozonizer, 310;
ozonizer, of Siemens, 292, 309; of Sie-
mens and Halske, 312 ; of Tindal, 313 ;
of Abraham and Marmier, 313 ; of
Parabolic mirrors, electrolytic produc-
tion of, 41.
Perchlorate, chemical formation, 84,
electrolytic formation, 99 ; technical
cells for, 126.
Pinch effect, 261.
Potassium, electrolytic production of, see
Potential, at liquid-liquid junctions, elim-
ination of, 15.
Potential measurement as method oi
Primary battery, denned, 142 ; Volta's
Smee's, Grove's, Bunsen's, chromic
acid cell, Leclanche's, 143 ; La-
lande's, 144 ; Daniell's, 145 ; dry cells,
146 ; Jacques's cell, 151 ; Jablochkoff 's
cell, 150 ; ideal carbon cell, 147 ; free
energy of, 148.
Quicking bath, 38.
deduction, electrolytic; denned, 68;
reducing power of cathode measured
by its potential, 69 ; pressure of hy-
drogen corresponding to different po-
tentials, 71 ; catalytic effect of cathode
on, 72 ; of chromic sulphate, 72 ; of
Secondary battery, defined, 142.
Series system of connection in metal
Silicon, electrothermic production, 219.
Silver plating, 38.
Silver refining, 57 ; Dietzel process, 57 ;
Moebius process, 59.
Sodium, production by electrolysis of
fused hydrate, 233; Castner cell for,
233 ; Ashcroft process, 234 ; uses of,
236; world's production, 235.
Steel, electrothermic refining of, 252 ;
Stassano's furnace, 254 ; Keller's,
254; Heroult's, 256; Girod's, 257;
Kjellin's, 259; Rochling and Roden-
Storage battery lead, history and con-
struction, 152-157 ; chloride cell, 154 ;
Gould cell, 156 ; theory of, 157-172 ;
chemical changes in, 157 ; change in
density of acid on charge and discharge,
158 ; electromotive force, 160 ; tem-
perature coefficient, 161 ; Le Blanc's
theory of, 161 ; Liebenow's theory,
163 ; charge and discharge curves,
165-167; capacity, 168; current effi-
ciency, 169 ; self-discharge, 169 ;
Tubes, electrolytic production of, 40.
Voltameter, see Coulometer.
White lead, electrolytic production of,
Wire, electrolytic production of, 40.
Zinc, electrolytic winning of, 45 ; spongy,
45, 46; refining, 67.
Zinc plating, 33.
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