Prep. Carbonate of potash, one pound; slaked lime, twelve ounces; distilled water, a gallon. Dissolve the carbonate in the water, and having heated the solution to the boiling point in a clean iron vessel, gradually mix it with the slaked lime, and continue the ebullition for ten minutes with constant stirring. Then set by, that the carbonate of lime may subside. Lastly, when the supernatant liquor has become perfectly clear, transfer it by means of a syphon to a well-stoppered green-glass vessel. In this process the lime, on account of its affinity for carbonic acid, abstracts it from the carbonate of potash, and thus carbonate of lime, which is insoluble, is precipitated, and potash remains in solution. [In the U. S. P. bicarbonate of potassa is employed instead of the carbonate, and the solution boiled till the excess of carbonate acid is given out. It is then decomposed by lime as in the text. The resulting preparation is stronger than that of the Br. Ph. having a sp. gr. of 1.065, and containing five and eight tenths per cent of hydrate of potassa.]

Prop. & Comp. Liquor potassae is a colourless liquid, with intensely acrid and caustic taste; sp. gr., 1.058. One fluid ounce requires for neutralization 48.25 measures of the volumetric solution of oxalic acid, equivalent to 22.68 grains of potash (KO). It does not effervesce when added to an excess of hydrochloric acid, nor give a precipitate with lime or oxalate of ammonia, showing the absence of carbonic acid and lime; and after being heated with nitric acid in excess, and evaporated to dryness, the residue forms with water a nearly clear solution, which is only slightly precipitated by chloride of barium and nitrate of silver, and is rendered very slightly turbid by ammonia, showing that mere traces of sulphates, chlorides, metallic impurities, or alumina are present; it forms with bichloride of platinum, the yellow double salt (K Cl, Pt Cl2). It injures glass containing lead by partially dissolving it; hence it is ordered to be kept in green-glass bottles.

Therapeutics. Liquor potassae, in large doses and undiluted, is a violent caustic poison; but taken into the stomach in a diluted form it acts at first as a direct antacid, neutralizing any free acid in the stomach; it also produces a powerful sedative effect upon the mucous membrane. After absorption into the blood, it possesses the power of increasing the change of tissues in the body, acting as an alterative, especially on the glandular system and on the secreting and excreting organs: it, doubtless, renders the blood more alkaline, and the fibrin less plastic; but from the small amount which can be taken on account of its causticity, never produces alkalinity in the urine previously strongly acid. It is used as an antacid in dyspepsia, but in the inflammatory forms of this affection its value depends more upon its sedative powers: it is also used in skin affections, and is especially useful when they depend upon a morbid condition of the stomach, as seen in erythema and other cutaneous diseases. As a blood alterant, liquor potassae has been employed in inflammation of serous membranes, attended with fibrinous depositions, as pleuritis, pericarditis, and periostitis, also in scrofula, syphilis, and chronic rheumatism. Recently, however, iodide of potassium has replaced this medicine in a great measure as an alterative. Externally, when freely diluted, liquor potassae may be employed as a wash in some chronic skin diseases.

Dose. 10 min. to 1 fl. drm., freely diluted.

Adulteration. Carbonate and sulphate of potash, chloride of potassium, and lime, all of which can be detected by the tests given above.