These values are taken from 'Electrochemical Equivalents' by Hering and Getman (New York 1917).

G. A. ROUSH, Assistant Secretary, American Electrochemical Society.

ELECTROCHEMICAL INDUSTRIES. Electrochemistry may be defined as that branch of chemistry relating to the carrying out of chemical reactions by the means of or with the assistance of electricity. The word electrochemical as here used includes the processes of electrometallurgy, the production and treatment of metals by means of electricity, there being no generic term covering both subjects.

The production or furtherance of chemical action by means of electrical energy may be secured in three ways: (1) By electrolysisthe action of an electric current upon a chemical compound in solution or in a fused condition; (2) by electrothermal action—the production of chemical changes by electrically generated heat; (3) by the discharge of electricity through

gases.

The largest employment of electrolysis is in the production and refinement of metals, particularly aluminum and copper; but it is also used extensively in the preparation of a large number of chemical compounds of widely varying character.

In most cases a substance obtained by electrolysis may be prepared also by a strictly chemical process. The choice of methods then becomes simply one of cost. An example in point is the manufacture of metallic sodium: originally discovered by the electrolysis of caustic soda, it was for many years made commercially by the reduction of sodium carbonate with carbon, or of caustic soda by a mixture of iron and carbon; more recently the electrolytic process has replaced the chemical methods, because it is cheaper. In other cases certain products of electrochemical action have not yet. been made by any other process.

A great saving of heat is found in most electrothermal processes, due to the fact that the electrically generated heat is applied inside the container, where it is effectively employed, no heat being wasted in heating the contents through the walls of the container, as in combustion processes. But even when produced by the cheapest water power, electric heat costs several times more than heat produced by the combustion of coal, so that where large quantities of heat are needed at only moderate temperatures, the combustion processes are usually cheaper.

We shall here consider the chief electrochemical industries that have thus far attained commercial importance.

Copper. The process of refining copper electrolytically consists in the transfer of copper from the anode to the cathode, by the selective action of the electric current, and in leaving the impurities behind dissolved in the electrolyte, or in the form of slime or sediment. The material at present subjected to profitable electrolyte refining is crude copper containing from 96 to 98 per cent pure copper, and varying amounts of silver, gold, platinum, palladium, nickel, iron, arsenic, antimory, sulphur, etc. This crude copper is obtained from various copper ores by smelting and is cast in copper molds into anode plates, which are about three feet square and one to two inches thick, weighing 250 to 500 pounds. The cathode plates are of electrolytically refined copper, practically the same in length and width as the anodes, but only 1/32 to 1/16 inch thick. The electrolyte, or bath, in which the plates are suspended, is a solution of copper sulphate just short of saturation, with enough sulphuric acid to prevent the separation of hydrated cupric oxide, but not enough to cause hydrogen instead of copper to be separated at the cathode; the proportions are about 3-4 per cent of conner as sulphate and 10-13 per cent of free sulphuric acid. When silver is present in the anode a little salt or hydrochloric acid is added to the electrolyte. The bath is kept at a temperature of about 40-60° C. (100-140° F.). The containing tanks are of wood, usually lined with sheet lead or carefully coated with a pitch compound, and of such dimensions that a distance of from 1.5 to 2 inches exists between the faces of the plates. In some cases the plates are arranged in series and in others in parallel or multiple. In the series system the anodes,

which are much smaller than in the multiple system, are suspended in the electrolyte from one-half to three-fourths of an inch apart, and only the end ones in the series are connected with the poles of the generator. With this arrangement the copper dissolved from the inner face of the first anode is deposited on the nearer face of the second plate; the farther face of the second plate is dissolved and deposited on the nearer face of the third plate and so on throughout the series. When the anodes are nearly exhausted the pure copper deposits are removed from the tank and the undissolved remnants of anode stripped from the back of the cathodes.

The series arrangement has the advantage of requiring electrical connections to be made at the first and last plates only, whereas the parallel system requires a connection at every plate; but in the series system the leakage of current due to the short-circuiting action of the sediment and sides of the tank is from 10 to 20 per cent, so that the parallel system is more generally used. The connections between the various plates and the circuit in the parallel systems are made by copper rods, which are run at two different levels along the edges of the tanks, one bar for each set of plates. In some instances these rods are of the inverted V shape, so that the edges will cut through any corrosion which may happen to form at the points of contact. The vats are arranged, with respect to each other, so that each is accessible from all sides and free circulation of the electrolyte is possible. This circulation is sometimes obtained by blowing a stream of air through the electrolyte, but more frequently by arranging the vats in steps, and piping so that the electrolyte may pass from the top of one vat to the bottom of the next, by the action of gravity. This maintains a uniform density of electrolyte, which is necessary for the proper formation of the deposit. The electromotive force required is from 0.2 to 0.4 volt per tank, with a current density of 15 to 20 amperes per square foot of cathode plate surface. The individual vats are connected in series so that the total voltage may be approximately the same as that which the generator furnishes, being usually 110 volts. One ampere of current deposits on the cathode only about one ounce of refined copper in 24 hours, and the current density must be kept below 40 amperes per square foot to avoid mushrooming and consequent short-circuiting. In practice from 400 to 500 ampere-hours are required per pound of copper deposited, the theoretical amount according to Faraday's law being only 386.2 ampere-hours. The loss varies from 4 to 20 per cent according to the system employed.

The main product of refining is commercial cathodes, which are sometimes shipped to consumers, but more frequently cast into wire-bars, ingots, cakes or slabs of standard dimensions and weight. They usually assay from 99.86 to 99.94 per cent pure copper. The yield in commercial cathodes is from 97 to 99 per cent of the anodes treated, excluding the anode scrap which varies in weight from 7 to 15 per cent of the original anode in parallel plants, but this scrap is not a loss as it is collected and recast into anode plates. Besides electrolytic copper most plants secure gold, silver, platinum

and palladium from the slimes, and sometimes selenium, tellurium and other rarer metals. Nickel salts are usually recovered from the solutions.

There are in the United States 10 electrolytic copper refineries with a total capacity of 2,780,000,000 pounds per year; one refinery in Canada with a capacity of 14,000,000 pounds per year. The actual production in 1917 was about 2,300,000,000 pounds, representing approximately 74 per cent of the entire world's production of copper for the year. Or, deducting from the total production the amount that does not require refining, about 275,000,000 pounds from Michigan, the United States production amounts to over 81 per cent of the total production of refined copper. The other 19 per cent is produced in a number of plants of comparatively small capacity in England, Wales and Continental Europe.

Aluminum.-Practically the whole output of this metal for the entire world is now produced electrolytically. The only process used on a large scale is that invented independently in 1886 by Charles M. Hall in the United States and by Paul L. T. Héroult in France. This process consists in electrolyzing alumina dissolved in a fused bath of cryolite. The alumina is obtained from the mineral bauxite which occurs abundantly in Arkansas, Georgia, Alabama and Tennessee. The natural material, being a hydrated alumina containing silica, iron and titanium, must be treated in order to drive off the water and eliminate the impurities. This is accomplished by a chemical process. In practice it requires about two pounds of alumina for each pound of aluminum produced. The flux or bath in which the alumina is dissolved consists of cryolite, a natural double fluoride of aluminum and sodium (AlF6NaF) found in Greenland. This is melted in a large carbonlined, sheet-iron tank which constitutes the negative electrode, a group of suspended carbon rods forming the positive electrode. A current of several thousand amperes at six to seven volts is used. Only a portion of this voltage is required to decompose the alumina, the balance amounting to about four to five volts represents the heat required to keep the bath melted. The passage of the current causes the aluminum to deposit on the bottom of the tank as a fused metal, whence it is drawn off periodically. The oxygen set free combines with the carbon of the positive electrodes and passes off as carbonic oxide. The reaction is AlO,+3C= 2A1+3CO. About one pound of carbon is consumed for one pound of aluminum produced. An excess of alumina is kept floating on the bath so that it is saturated at all times. cording to Faraday's law the weight of aluminum deposited by 1,000 amperes is 0.743 pound per hour. The actual yield of metal by the Hall process is about 85 per cent of this theoretical amount. The metal when drawn from the tanks is cast into rough ingots which are afterward remelted and converted into commercial shapes, such as sheets, rods, wires, etc. The United States in 1917 produced about 180,000,000 pounds of aluminum, which was about two-thirds the total production of the world. Before the European War the share of the United States in the total production was under 50 per cent.

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which are much smaller than in the multiple system, are suspended in the electrolyte from one-half to three-fourths of an inch apart, and only the end ones in the series are connected with the poles of the generator. With this arrangement the copper dissolved from the inner face of the first anode is deposited on the nearer face of the second plate; the farther face of the second plate is dissolved and deposited on the nearer face of the third plateand so on throughout the series. When the anodes are nearly exhausted the pure copper deposits are removed from the tank and the undissolved remnants of anode stripped from the back of the cathodes.

The series arrangement has the advantage of requiring electrical connections to be made at the first and last plates only, whereas the parallel system requires a connection at every plate; but in the series system the leakage of current due to the short-circuiting action of the sediment and sides of the tank is from 10 to 20 per cent, so that the parallel system is more generally used. The connections between the various plates and the circuit in the parallel systems are made by copper rods, which are run at two different levels along the edges of the tanks, one bar for each set of plates. In some instances these rods are of the inverted V shape, so that the edges will cut through any corrosion which may happen to form at the points of contact. The vats are arranged, with respect to each other, so that each is accessible from all sides and free circulation of the electrolyte is possible. This circulation is sometimes obtained by blowing a stream of air through the electrolyte, but more frequently by arranging the vats in steps, and piping so that the electrolyte may pass from the top of one vat to the bottom of the next, by the action of gravity. This maintains a uniform density of electrolyte, which is necessary for the proper formation of the deposit. The electromotive force required is from 0.2 to 0.4 volt per tank, with a current density of 15 to 20 amperes per square foot of cathode plate surface. The individual vats are connected in series so that the total voltage may be approximately the same as that which the generator furnishes, being usually 110 volts. One ampere of current deposits on the cathode only about one ounce of refined copper in 24 hours, and the current density must be kept below 40 amperes per square foot to avoid mushrooming and consequent short-circuiting. In practice from 400 to 500 ampere-hours are required per pound of copper deposited, the theoretical amount according to Faraday's law being only 386.2 ampere-hours. The loss varies from 4 to 20 per cent according to the system employed.

The main product of refining is commercial cathodes, which are sometimes shipped to consumers, but more frequently cast into wire-bars, ingots, cakes or slabs of standard dimensions and weight. They usually assay from 99.86 to 99.94 per cent pure copper. The yield in commercial cathodes is from 97 to 99 per cent of the anodes treated, excluding the anode scrap which varies in weight from 7 to 15 per cent of the original anode in parallel plants, but this scrap is not a loss as it is collected and recast into anode plates. Besides electrolytic copper most plants secure gold, silver, platinum

and palladium from the slimes, and sometimes selenium, tellurium and other rarer metals. Nickel salts are usually recovered from the solutions.

There are in the United States 10 electrolytic copper refineries with a total capacity of 2,780,000,000 pounds per year; one refinery in Canada with a capacity of 14,000,000 pounds per year. The actual production in 1917 was about 2,300,000,000 pounds, representing approximately 74 per cent of the entire world's production of copper for the year. Or, deducting from the total production the amount that does not require refining, about 275,000,000 pounds from Michigan, the United States production amounts to over 81 per cent of the total production of refined copper. The other 19 per cent is produced in a number of plants of comparatively small capacity in England, Wales and Continental Europe.

Aluminum.- Practically the whole output of this metal for the entire world is now produced electrolytically. The only process used on a large scale is that invented independently in 1886 by Charles M. Hall in the United States and by Paul L. T. Héroult in France. This process consists in electrolyzing alumina dissolved in a fused bath of cryolite. The alumina is obtained from the mineral bauxite which occurs abundantly in Arkansas, Georgia, Alabama and Tennessee. The natural material, being a hydrated alumina containing silica, iron and titanium, must be treated in order to drive off the water and eliminate the impurities. This is accomplished by a chemical process. In practice it requires about two pounds of alumina for each pound of aluminum produced. The flux or bath in which the alumina is dissolved consists of cryolite, a natural double fluoride of aluminum and sodium (AlF6NaF) found in Greenland. This is melted in a large carbonlined, sheet-iron tank which constitutes the negative electrode, a group of suspended carbon rods forming the positive electrode. A current of several thousand amperes at six to seven volts is used. Only a portion of this voltage is required to decompose the alumina, the balance amounting to about four to five volts represents the heat required to keep the bath melted. The passage of the current causes the aluminum to deposit on the bottom of the tank as a fused metal, whence it is drawn off periodically. The oxygen set free combines with the carbon of the positive electrodes and passes off as carbonic oxide. The reaction is Al2O3+3C= 2A1+3CO. About one pound of carbon is consumed for one pound of aluminum produced. An excess of alumina is kept floating on the bath so that it is saturated at all times. cording to Faraday's law the weight of aluminum deposited by 1,000 amperes is 0.743 pound per hour. The actual yield of metal by the Hall process is about 85 per cent of this theoretical amount. The metal when drawn from the tanks is cast into rough ingots which are afterward remelted and converted into commercial shapes, such as sheets, rods, wires, etc. The United States in 1917 produced about 180,000,000 pounds of aluminum, which was about two-thirds the total production of the world. Before the European War the share of the United States in the total production was under 50 per cent.

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