ELECTROCHEMICAL INDUSTRI,ES. Electrochemistry may be defined as that branch of chetnistry relating to the carrying out of chemical reactions by the means of or with the assistance of electricity. The word electro chemical as here used includes the processes of electrornetallurgy, the production and treat ment of metals by means of electricity, there being no genenc term covering both subjects.
The production or furtherance of chemical action by means of electrical energy may be secured in three ways: (1) By electrolysis — the 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 electncity through gases.
The largest employment of electrolysis is in the production and refinement of metals, par ticularly aluminum and copper; but it is also used extensively in the preparation of a large number of chemical compounds of widely vary ing character.
In most cases a substance obtained by elec trolysis may be prepared also by a strictly chem ical process. The c,hoice of methods then be comes simply one of cost. An example in point is the manufacture of metallic sodium: onginally discovered by the electrolysis of caustic soda, it was for many years made com mercially by the reduction of sodium carbonate with carbon, or of caustic soda by a mixture of iron and carbon; more recently the electro lytic 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 com bustion 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 quan tities of heat are needed at only moderate tem peratures, the combustion processes are usually cheaper.
We shall here consider the chief electro chemical industries that have thus far attained commercial importance.
Copper.—The process of refining copper electrolytically consists in the transfer of cop per 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 sedi ment. The material at present subjected to profitable electrolyte refining is cru e copper containing f rom 96 to 98 per cent pure copper, and varying amounts of silver, gold, platinum, palladium, nickel, iron, arsenic, antimory, sul phur, 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 sus pended, 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 in stead of copper to be separated at the cathode; the proportions are about 3-4 per cent of copper 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 kern at a temperature of about 40-60° C. (100-160° F.). The contain ing 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 ar ranged 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 ar rangement 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 depos ited 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.