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Tests for the Precious Metals

For Gold.

To a diluted colorless solution of chloride of gold, add a few drops of a solution of any salt of tin; or stir the solution of gold with a slip of metallic tin; in either case, the production of a beautiful purple or port wine color will be the immediate result. If the mixture is allowed to settle, it becomes colorless; a purple powder (which is an oxide of gold combined with a little tin) being precipitated. This powder is employed in the painting of china, and is called the purple precipitate of Cassius. For Silver. into a glassful of water, and add to it a grain of common salt. Mutual decomposition of the salts will take place, and chloride of silver (in the form of a white powder) will be precipitated. This precipitate is soluble in ammonia, and blackens on exposure to light.

For Copper.

Add a few drops of a solution of nitrate of copper to a test glass of water; the mixture will be colorless; pour into it a little liquid ammonia.

The mixture will then assume a fine deep blue color.

Another. Ferrocyanide of potassium gives a dense brown precipitate with the salts of copper.

Let fall a drop of a solution of nitrate of silver | This is very delicate.