For the preparation of chemically pure tin two methods are employed.
Thus, for instance, chemically pure iron in the ingot has the specific gravity 7.844; when it is rolled out into thin sheet, the value falls to 7.6; when drawn into thin wire, to 7.75.
Hampe prepared chemically pure bismuth by fusing the metal with sodium carbonate and sulphur, dissolving the bismuth sulphide so formed in nitric acid, precipitating the bismuth as the basic nitrate, redissolving this salt in nitric acid, and then precipitating with ammonia.
Stas, in his stoichiometric researches, prepared chemically pure bromine from potassium bromide, by converting it into the bromate which was purified by repeated crystallization.
To obtain the metal chemically pure a specially prepared pure oxide or salt of zinc is distilled.