The Acker process, which was formerly used at Niagara Falls, but which has been discontin ued, obtained caustic soda and chlorine using molten lead in place of mercury as a cathode, fused salt instead of brine as the electrolyte, and operated at a temperature of 850° C. F.). The containing tank was a cast-iron vessel 5 feet long, 2 feet wide and 1 foot deep, the sides above the molten lead being covered with magnesia so that the current must pass from the graphite anodes to the lead which acted as the cathode. At one end of the tank was a small compartment separated from the re mainder of the vessel by a partition dipping into the lead to such a depth that nothing but this fused lead can pass from one compart ment to the other. In the smaller compartment the lead was subjected to a stream of steam, which decomposed the lead-sodium alloy with the formation of NaOH and hydrogen and at the same time kept the alloy in circulation. At intervals the caustic, which was in a fused of state, was drawn o and allowed to solidify, thus avoiding the evaporation of water which is necessary in the Castner-Kellner process. The current employed per vessel in the Acker process was 2100 amperes at from 6 to 7 volts, of which energy 54 per cent is used in chemical action, and the remainder in maintain ing the temperature. The output of each was 550 pounds of caustic soda and 450 pounds of chlorine in 24 hours.
processes making caustic soda from salt at the same time produce chlorine gas at the anode. In some cases this is absorbed in lime for the manufacture of bleaching powder, and in other cases it is compressed and liquefied. The liquid chlorine is shipped in pressure tanks for chemical purposes and for water purifica tion. One of the most striking uses to which it has been put is as one of the poison gases used at the front in trench warfare. Hundreds of tons of gas have been used in a single attack.
electrochemical in dustry that is widely distributed throughout the country is the manufacture of hypochlorite for bleaching purposes. For some time the use of hypochlorite as a bleach was confined to large installations where an enormous quantity of bleaching liquor was demanded every day, e.g., in the manufacture of paper pulp. Now hypo.
chlorite plants are installed in small units, pro ducing only a few gallons of bleach a day for use in laundries. The types of cell used in hypochlorite manufacture vary widely, but are all alike in that they must have unattackable electrodes of some kind, usually either graphite or platinum. Many of the different types of cells have a number of electrodes in series, acting as bipolar electrodes. The electrolyte used is a 15 to 16 per cent solution of common salt, NaCl.
The efficiency of the operation in practice usually amounts to only about 20 to 25 per cent, but the simplicity and ease of working of the process commend it in spite of its low energy efficiency. The minimum requirement is 127 kilowatt hours for the production of 1 kilogram of active chlorine, while actual practice requires 6 to 7 kilowatt hours.
Potassium Chlorate is produced electro chemically in considerable quantities, both here and abroad. The Gibbs process, used at Niagara Falls, consists in the electrolysis of potassium chloride solution, using a copper or iron cathode and a platinum anode. The current density is high, being 500 amperes per square foot of anode. Each cell uses about four volts, of which 1.4 is required to convert chloride to chlorate, and the remainder produces the heat that maintains the electrolyte at from 50° to 70° C. (125° to 160° F.), which is necessary for the proper reaction. The whole commercial supply is thus produced. Perchlorates are made by elec trolyzing chlorates at low temperatures in the same type of cell.
Hydrogen and One of the most widely distributed of the electrochemical indus tries, but one that is usually installed in fairly small units, is the electrolysis of water for the production of hydrogen or oxygen, or both. When only one of the gases is required it is often more economical to produce it by some other method, but if both gases are needed, it is better to use an electrochemical method, and often the conditions are such that the single gas can be produced advantageously by the electro chemical method.
Apparatus for the commercial electrolysis of water uses as electrolyte a solution either of sulphuric acid (11.804), or one of the alkalies (NaOH or KOH). With the alkalies the cells are usually constructed of iron, and with the acid, they must be lined with lead, whatever the body of the cell may be. With the alkaline solu tions, a concentration of 10 to 25 per cent is used, and with acid, 20 to 30 per cent. The voltage needed to force a current through such a cell is composed of three factors — the voltage of decomposition of the water, the voltage nec essary to overcome the resistance of the cell, and the voltage necessary to overcome the re sistance of the gas layers on the electrodes, sometimes known as uovervoltage? The sul phuric acid solution has a much better con ductivity than the alkaline solutions, but the resistance of the gas films is greater on lead than on iron, so that on the whole, cells using alkaline solutions have a lower working voltage than those using acid. The current efficiency in either case can be made to approach 100 per cent.