Alkalies.

Alkalies. The word alkali is of Arabic origin, kali being the name of the plant from the ashes of which an alkaline substance was first procured. The name now denotes a class of substances having similar properties. The alkalies proper are four in number—potash, soda, lithia, and ammonia. The first three are oxides of metals; the last is a compound of nitrogen, hydrogen, and oxygen, and, being in the form of a gas, is called the volatile alkali. Potash, being largely present in the ashes of plants, is called the vegetable alkali; and soda, predominating in the mineral kingdom, is designated the mineral alkali. The alkaline earths, as they are called—lime, magnesia, baryta, and strontia—are distinguished from the former by their carbonates not being soluble in water. The distinguishing property of alkalies is that of turning vegetable blues green, and vegetable yellows reddish brown. Blues reddened by an acid are restored by an alkali. The alkalies have great affinity for acids, and combine with them, forming salts, in which the peculiar qualities of both alkali and acid are generally destroyed; hence they are said to neutralise one another. In a pure state, alkalies are extremely caustic, and act as corrosive poisons. Combined with carbonic acid, especially as bicarbonates, they are used to correct acidity in the stomach; but the injudicious and continued use of them is attended with great evil. The alkalies and some of their salts (e.g. citrates, tartrates) are also used to increase the secretion of urine, and (ammonia excepted) to diminish its acidity. Ammonia in small doses is a powerful stimulant. An account of the several alkalies will be found under the heads of POTASH, SODA, LITHIA, and AMMONIA; and of the alkaline earths, under LIME, MAGNESIA, BARYTA, and STRONTIA.