ELECTRIC TURBINE

See Tursivn GINES. branch of the science in which chemical changes are brought about by electric a l Means. Strictly speaking, this includes only those proce es involving electrol ysis—t.e. the decomposition of a compound by the pa age of an electric current, and the liberation of the composing elements at the two poles. Electrothermal proce es, however, depending on high temperatures which are obtained by electrical means, are frequently included in the electro-chemical field. Among such proce es may be mentioned. the manufacture of artificial graphite, carborundum and calcium carbide, and many metallurgical proce es, all of which are carried out in electric furnaces of various types. Strictly electrochemical proce es depend upon the fact that when a direct current pa es. through a solution of a compound, or through the compound itself in a fused. condition, the compound is split up into. its composing elements, the metallic radicle being liberated at the kathode (or negative pole) and the acid radicle at the anode (or positive pole). Before such decomposition can occur it is nece ary that the voltage should reach what is known as the ‘decomposition voltage’ this figure varying with different compounds. Moreover, the amount of metal deposited at the kathode is proPortional to the current and also varies with different metals. The number of grams of metal deposited per second by a current of one ampere is known as the ‘electro-chemical equivalent’ of the metal. The value for silver is 0.00111827 and the corresponding value for any other metal may be found by multiplying the above figure by the chemical. equivalent of the metal and dividing by 107°88. In other words, the electrochemical equivalents are proportional to: the chemical equivalents. include metallic plating, the refining of” various metals and the manufacture of sodium, pota ium, chlorine and caustic soda. Copper is refined by the electrolysis of a solution of copper sulphate, and a similar solution is used for copper plating. In the case of silver a solution of the nitrate is used, while gold is refined and plated from a chloride solution. Zine is deposited from zinc sulphate solutions, and galvanizing of iron is. carried out electrolytically from solutions of the sulphate, chloride or cyanide. Other metals, either recovered or refined. by electrolysis, include lead, cadmium, antimony, nickel, bismuth and tin. The. manufacture of chlorine and caustic soda is a typical electro-chemical pro-. ce . A solution of brine is used as the electrolyte, and a current of high amperage and low voltage is through it, splitting it up mto which is evolved at the anode and which is deposited at the kathode. sodium combines readily with water, metal is not recovered as such, but diately forms the hydroxide soda). In order to prevent reaction between the chlorine and ‘soda, which would result in the formation of hypochlorites, the anodes are rated from the kathodes by a diaphragm, which permits the ‘of the electric current and of the trolyte, but prevents the pa age of products of electrolysis. The anodes usually made of graphite or other of hard carbon, and the kathodes sheet steel or iron. The diaphragms made of asbestos or a mixture of and cement. In the manufacture sodium, an electrolyte of fused hydroxide or sodium chloride’is in place of the solution.