POTASSIUM 761 down to a small bulk and left to cool, when the carbonate separates in small crystals. A purer salt may be obtained by igniting cream of tartar in a crucible, which produces a mix- ture of dipotassic carbonate and charcoal (black flux). The salt is obtained by digestion in wa- ter, filtration, and evaporation. It is very sol- uble in water, one part of the anhydrous salt dissolving in 1-05 part of water at 37*4 F. and in 0'49 part at 158. It contains in 100 parts 68-17 of dipotassic oxide, and 31-83 of carbonic acid; specific gravity 2-267. It crystallizes from an aqueous solution in oblique rhombic octahedral crystals, containing two equivalents of water (K 2 CO 3 + 2H 2 O), which are very deli- quescent. Its reaction with test paper is strong- ly alkaline, and it has an acrid alkaline taste. The anhydrous salt fuses at a red heat and is partially volatilized at a high temperature. When it is heated to redness with silica, the latter unites with the oxide, forming silicate of potassium ; and advantage is taken of this af- finity in the analysis of mineral substances con- taining much silica. Dipotassic carbonate is extensively used in the arts, as in the manufac- ture of soap and glass, and in preparing caustic potash and other chemical compounds for the purposes of pharmacy and chemistry. The monopotassic carbonate, commonly called bi- carbonate of potash, is obtained by passing car- bonic acid gas into a solution of the normal carbonate in five parts of water. The bicar- bonate, being much less soluble than the nor- mal salt, is precipitated, and being collected on a filter, pressed, and redissolved in warm wa- ter, crystallizes on cooling in large rhomboidal prisms belonging to the monoclinic system, which are soluble in four parts of cold and five sixths their weight of boiling water, and are nearly insoluble in alcohol. Bicarbonate of potash is much used in chemistry when a pure potassium salt is required, and is an important article of the pharmacopoeia. Its medicinal properties are similar to those of the carbon- ate, and being milder in its action it is general- ly preferred. It is used as an antacid in some forms of dyspepsia; in acute rheumatism, for which it is a standard remedy, and also in many cutaneous affections. It increases the alkalinity of the blood, and facilitates glandular secretion, for which reason it is beneficial in most forms of fever and inflammatory diseases. 9. Nitrate of potassium (nitre, saltpetre) is de- scribed in the article NITRATES. 10. The prin- cipal sulphates of potassium are a normal or neutral sulphate and an acid sulphate. Nor- mal or bipotassic sulphate, K 2 SO 4 (nitrum vitriolatum, tartarm mtriolatus, specificum purgans Paracelsi), occurs native in delicate needle-shaped crystals, or as a crust on many Vesuvian lavas, and in this form is often called glaserite, arcanite, aphthalose, and Vesuvian salt. It exists also in solution in sea and min- eral waters, and in vegetable and animal fluids. It is obtained as a by product in several manu- facturing processes, as in the manufacture of nitric acid from saltpetre, where the residue, consisting principally of acid sulphate, is neu- tralized with crude potassic carbonate. The hot solution on cooling yields crystals of nor- mal sulphate, either in four-sided oblique rhom- bic prisms, or in six-sided pyramids, belong- ing to the trimetric system. They are anhy- drous, require about 12 parts of water at 32 F. for solution, and are composed in 100 parts of dipotassic oxide 54-07, and sulphuric anhy- dride 45-93; specific gravity 2'66. They are insoluble in alcohol, and decrepitate strongly when heated. Sulphate of potash is a mild purgative, but is used in medicine principally as an ingredient of Dover's powder, or pulms ipecacuanha compositus. The acid, or mono- potassic sulphate, KHS0 4 , commonly called bisulphate of potash, is formed by mixing the neutral sulphate with half its weight of oil of vitriol, evaporating to dry ness in a platinum vessel, and dissolving the fused salt in hot wa- ter, from which it crystallizes on cooling, in flattened rhombic prisms, which dissolve in two parts of water at 60 F., and in less than one part of boiling water. It occasionally crys- tallizes in anhydrous needles having the for- mula K 2 SO 4 ,SO 3 . 11. Chlorate of potassium, or potassic chlorate, commonly called chlorate of potash, is analogous in composition to chloric acid (HC10 3 ), the difference being in the sub- stitution of an equivalent of potassium for one of hydrogen. When chlorine gas is passed into a hot solution of potash or carbonate of potash, the liquid yields on cooling crystals of chlorate of potassium, KClOa. The salt is made in this indirect way instead of adding chloric acid to potash, and precedes the formation of the acid, which is obtained by boiling the salt in a solution of hydrofluosilicic acid. It is a simple example of chemical substitution, a sub- ject the study of which has thrown much light upon the science of chemistry. Chlorate of potash is prepared in the large way by con- verting milk of lime into a mixture of calcic chlorate and chloride with an excess of chlo- rine, and adding potassic chloride, by which the calcic chlorate is decomposed (Ca2ClO 3 + 2KCl=2KC10 3 + CaCl 2 ). The potassic chlo- rate, being sparingly soluble, is easily separated from the very soluble calcic chloride by evapo- ration, and deposited in six-sided prisms, which being redissolved in boiling water again crys- tallize in six-sided plates belonging to the mono- clinic system. They dissolve in about 16 parts of water at 60 F., and in about 1-6 part of boiling water. When heated, the salt gives off the whole of its oxygen, chloride of potas- sium remaining; a perchlorate is formed in the early stages of the decomposition. Chlo- rate of potash is a powerful oxidizing agent, and detonates violently when mixed with cer- tain organic bodies and heated or struck with a hammer. If mingled with flowers of sulphur and triturated in a mortar, it produces a series of sharp detonations. It is used in the manu- facture of lucifer matches, in percussion caps,
