addition of sodium acetate; it is then precipitated as a basic sulphate containing zinc.”[355]
[355] Various other processes are given in ‘Watts’ Dictionary.’
Indium may be obtained in the metallic state from the reduction of its oxide by means of hydrogen; charcoal or carbonaceous fluxes are not good reducing agents, as their employment necessitates a very high temperature, and loss from volatilisation occurs. Sodium is found to be the best reducing agent when large quantities of the metal are required.
Böttger’s method is to precipitate the indium by zinc, to press the spongy metal so obtained in hot water, then to submit it to pressure in a screw press between filtering paper, and finally to melt it with cyanide of potassium.
Prop. Indium is a soft, white, durable metal, somewhat resembling cadmium, wholly destitute of crystalline structure. Its specific gravity, which is 7·421 at 16·8° C., is not altered by rolling or hammering. When heated in the air to 176° C., it melts without becoming oxidised; at a temperature above this, however, it becomes covered with a coating of suboxide, becoming gradually changed into the yellow sesquioxide. Indium is less volatile than either cadmium or zinc. It dissolves slowly in dilute sulphuric and hydrochloric acids, hydrogen being given off. In strong hydrochloric acid it dissolves rapidly. Nitric acid oxidises it, evolving at the same time nitric oxide; whilst sulphuric acid converts it into anhydrous sulphate.
When examined by means of the spectroscope, the flame of indium reveals two brilliant bands—a violet and a blue one.
Indium is completely precipitated from a solution of its acetate, as well as from neutral solutions of its salts in general, by sulphuretted hydrogen. Ammonia, neutral sodium carbonate, and acid sodium carbonate, throw down white precipitates insoluble in excess of the precipitant; caustic potash and soda produce a white precipitate of indium hydrate, soluble in excess. Barium carbonate precipitates it completely. Potassium ferrocyanide gives a white precipitate.
Estim. “The most convenient method of estimating indium is by precipitating it as hydrate with ammonia, dissolving the washed precipitate in hot dilute nitric acid, evaporating, igniting, and weighing the oxide thus obtained. Precipitation with sulphuretted hydrogen does not give exact results on account of the solubility of the indium sulphide.”[356]
[356] Watts.
Indium forms compounds with bromine, chlorine, iodine, oxygen, and with several of the organic and inorganic acids.