Prep. By dissolving platinum in aqua regia, with heat. A mixture of half a fluid ounce of nitric acid with three fluid ounces of hydrochloric acid, and two fluid ounces of distilled water, are poured upon a quarter of an ounce of platinum foil in a small flask, and digested, more of the acid mixed in the same proportion being added until the metal is dissolved. The solution is transferred to a porcelain capsule, a fluid drachm of hydrochloric acid added, and the whole evaporated on a water-bath until acid vapours cease to be given off. The residue is dissolved in five ounces of distilled water and preserved in a stoppered bottle.

Prop., Comp. & Use. The solution is of a dark reddish-yellow colour, is used as a test for potassium, forming with the chloride of that metal a sparingly soluble double salt, which distinguishes potash from soda salts. The composition of bichloride of platinum (Pt Cl2). It also precipitates ammonia salts, and many of the alkaloids, as nicotine, etc.