Prep. From pearl-ashes (made from the ashes of wood) by solution in a small amount of water and crystallization, in which process most of the other salts contained in the wood are left undissolved. By heating the crystallized bicarbonate to redness, a very pure dry carbonate of potash is obtained.
Prop. & Comp. Carbonate of potash forms small white and rather opaque crystalline grains, having a strong alkaline taste; it deliquesces in the air, and is almost entirely soluble in water (quite so, if pure); insoluble in spirit, effervescing with dilute hydrochloric acid, and forming a solution with which bichloride of platinum gives a yellow precipitate; when supersaturated with nitric acid and evaporated to dryness, the residue is almost entirely soluble in water, only a little silica remaining undissolved, and the solution is precipitated only faintly by chloride of barium or nitrate of silver. Composition (KO, Co2 + 2 HO). The salt loses about 21 per cent. of its weight when exposed to a red heat. 87 grains require for neutralization at least 98 measures of the volumetric solution of oxalic acid, equivalent to about 46 grains of potash. It should be kept in a well-stoppered bottle.
Therapeutics. Almost the same as of potash, but is much less caustic, and hence more of the alkali can be introduced into the system; after absorption its effects are the same. Sometimes employed externally.
Dose. 10 gr. to 20 gr.
Adulteration. Sulphates and chlorides are very apt to be present; detected by the tests above given.