Potassium decomposes hydrofluoric acid, and forms fluoride of potassium (KF). It crystallises in cubes.
Silica-fluoride of potassium (KF, falls as a transparent gela tinous precipitate on adding hydrotluo.silicic acid to a salt of potash. Its formation is sometimes used as a test for potash.
Carbonate of potash (KO, This salt is imported in large quan tities from Russia and America. It is procured from plants, which for this purpose are burned in dry pits three or four feet deep, the ashes dissolved in water, evaporated until the phosphates, sulphates, chlo rides, &c., crystallise out, and the mother liquor then boiled to dry ness. Such is the crude potash or pearlash of commerce ; it varies very much in quality, but its value is always determined by the process of ALKALISIETITY. After recrystaUiation till pure, it is sent into the market as salts of tartar, or purified pearlas7ies.
Chemically pure carbonate of potash may be obtained by heating the bicarbonate to a little below redness, or by deflagrating a mixture of equal parts of nitrate and bitartrate of potash : either product is digested in water, filtered, and evaporated to the crystallising point.
Carbonate of potash crystallises in deliquescent, oblique, rhombic octohedra, containing two equivalents of water of cryatalhisation (KO CO,+2Aq.). It has an acrid, soapy taste, is strongly alkaline to test paper, is soluble in rather more than its own weight of cold water, and in rather less than half its weight of hot water. The strength of its solution may be ascertained by its specific gravity according to Tunner man's table :— Carbonate of potash is insoluble in alcohol. It fuses at a red heat, and slowly volatilises at a still higher temperature.
Carbonate of potash is largely used in the manufacture of soap and of glass, and is a convenient salt for the preparation of other potash compounds.
Bicarbonate of potash (KO, is formed when moist car bonate of potaah is exposed to the influence of a current of carbonic acid. It forms permanent right-rhombic prisms. Its solution is neutral to test-paper, and by long exposure to air or a boiling tempe rature is gradually reduced to the state of solution of sesepticarbonate.
Borates of potash. There are several of these. The biborate crystallises in six-aided prisms, and resembles borax. [Bonier° Am.] Phosphates of potash. The different varieties of phosphoric acid [Pnosrnoaus] form salts with potash, but the resulting compounds have no particular interest.
Sulphite of potash (KO, SO,) and bisulphite of potash (KO, HO, 2S0,) may readily be obtained, but the corresponding soda-salts [SODIUM] are nearly always used in their place.
Sulphate of potash (KO, SO,). Sal polyehrest. Bisulphate of potash is neutralised with carbonate, and evaporated ; the resulting sulphate of potash much resembles quartz in appearance. It requires 16 parts of cold water for solution, but is much more soluble in hot water. It is very hard, and forms double salts with many other protosulphates, and with those sesquisulphatea that are isomorphous with sesquisul phate of alumina. [Alums.] Bisulphate of potash (KO, HO, Sal enixum. A bye-product in the distillation of hydrochloric or nitric acids. It is much more soluble in water than the neutral sulphate, and crystallises in prisms or platens.
A sesguisulphate of potash (2(KO, SO,) + HO, S0,1 also exists.
Ilypochlorite of potash, chloride of potash, or chlorinated solution of potash (KO, CIO + K, Cl for 2(KO, Cl) = KC1 +KO, C10). Obtained on passing chlorine into solution of potash. It is a disinfectant ; but the corresponding soda-salt is more generally used.
Chlorate of potash (KO, C10,), oxymuriate of potash, is formed on passing chlorine gas into a mixture of 69 parte of carbonate of potash with the slaked lime that is obtained from 168 parts of quick lime. The resulting mass is lixiviated with water, and evaporated till the chlorate crystallises out. The decomposition is thus expressed Chlorate of potash is soluble in 16 parts of cold water, but in less than twice its weight of boiling water. It has a cooling saline taste. When heated, it parts with the whole of its oxygen. [OxvoKs.] It is a powerful oxidising agent, and is used in certain operations connected with calico-printing and in the manufacture of lucifer matches.