This metal occurs in very small proportions in some zinc - blendes. It is best prepared from metallic zinc from Freiberg, Saxony, which contains about 1/10 per cent., in the following manner: - The zinc is almost completely dissolved in hydro chloric acid, and, after standing 2 or 3 days, the indium is precipitated on the zinc remaining undissolved. The indium powder is washed off the zinc, and a few drops of dilute sulphuric acid are added to dissolve any basic zinc chloride formed; the spongy metal is well washed with hot water and treated with nitric acid; the unfiltered acid solution is boiled with excess of sulphuric acid till all the nitric acid is driven off; the solution is filtered, the residue is well washed, and large excess of ammonia is added to the filtrate; the cadmium, copper, and zinc mostly remain in solution, while all the indium, iron, and lead are deposited; this latter residue is well washed, dissolved in a little hydrochloric acid, treated with excess of hydric - sodic sulphite, and boiled till sulphur'us acid fumes cease; the precipitate formed is indium sulphite, which is purified by solution, and boiling in sulphurous acid; the pure salt decomposes when strongly heated, leaving a residue of indium oxide, which can be reduced to metal either by ignition in a current of hydrogen or by fusion with sodium.

The latter plan is the better for dealing with any quantity, and is thus carried out: - The finely - divided oxide is packed in alternate layers with thin slices of sodium in a porcelain crucible, and covered with a thick coat of anhydrous sodium chloride; the porcelain crucible and its contents are put into a covered Hessian crucible, and gently heated till the reaction is complete, when the temperature is increased to moderate redness; the brittle alloy obtained is boiled several times in water, washed with alcohol and ether, and re - fused under potassium cyanide; the last traces of sodium are removed from the regulus by throwing it, in small pieces, into fused soda carbonate, when the indium is obtained pure. It is a malleable metal, softer than lead, of a white colour, and noncrystalline; it dissolves rapidly in nitric acid and slowly in hydrochloric and dilute sulphuric; it has a sp. gr. of 7.42, melts at 349° F. (176° C), and retain its lustre even in boiling water.