SODIUM HYDROXIDE. SODIUM HYDRATE. OR C.uts rIC NaOH, This is of importance next to dium carbonate only. on account of its use in enormous quantities in refining fats and vegetable oils. and in the manufacture of soap. In appear ance it is a white solid, strongly caustic and high ly deliquescent. It is readily soluble in water, with evolution of heat, and by cooling a concen trated solution to 8° C.. a deposit of crystalline sodium hydrate (2NaOH + 71111) is obtained.
Sodium hydroxide is one of the strongest alka lies known. On a large scale it is manufactured by the action of milk of lime (calcium hydrate) upon a boiling solution of sodium carbonate. whereby calcium carbonate is precipitated, and sodium hydrate remains in the solution. The re action is (OH) After the removal of the solid calcium carbonate the solution is evaporated, and finally yields the solid sodium hydrate. One of the chief sources of supply is the tank liquor. produced in the manufacture of sodium carbonate by the Leblanc process (see above). The tank liquor, contain ing essentially sodium carbonate and sodium hy drate, is heated to boiling and an excess of lime is stirred into the mixture. The sodium sulphide present in the tank liquor is oxidized to sodium sulphate by the combined action of air injected into the mixture and of sodium nitrate. which is added for the purpose. The solid calcium carbo nate is separated by filtration. The action of so dium nitrate is shown by the following equation: The oxygen set free reacts upon the sodium sul phides present, and converts them into the sul phate.
In recent years sodium hydrate has been manu factured to a considerable extent by the electrol ysis of brine, also by the direct electrolysis of fused common salt. The two most recent electro lytic processes are the Aussig 'bell process' and the Acker process. The former has been under development at Aussig. The broad features of the method are illustrated in Fig. 2. In this dia gram, a represents the anode, b the solution of common brine which forms the electrolyte, a the hell, and e the cathodes; e is the pipe through which fresh brine is supplied and g serves to carry away the chlorine gas. The caustic alkali solution overflows through the pipe f. A cur rent efficiency of from 85 to 90 per cent. is claimed and the strength of the alkali solution varies between 100 and 150 grains of caustic soda per liter.
In the Acker fusion process, which is employed at Niagara Falls, N. V., the electrolyte consists of fused salt and the cathode of molten lead; a diagrammatic sketch of the cell is shown in Fig. 3. K represents the connections between the bus bar and the anodes G, F the cell walls, 11 the upper level of the fused salt electrolyte, which overlies the molten lead cathode 1. A steam jet at the side of the cell circulates the molten lead cathode, and the decomposition of the lead-so dium alloy produced is accomplished in a sepa rate vessel.