the action of chlorine gas, to saturation (the gas is absorbed with great rapidity, the temperature rises above 212° Fahr., and water is freely evolved); the heat, with free exposure, is then maintained at 212° for a few minutes (to remove some trace of ‘hypochlorite’), the residuum, consisting of chlorate of potassium and chloride of calcium, is treated with hot water, and the chlorate of potassium crystallised out of the resulting solution, as before. This process, which is an excellent one (the loss of potassium being for the most part avoided), has been modified and improved by various authorities, as will be seen below.
5. A solution of chloride of lime (18° to 20° Baumé) is heated in a leaden or cast-iron vessel, and sufficient of a salt of potassium added to raise the density of the liquid 3 or 4 hydrometer degrees; the solution is then quickly, but carefully, concentrated until the gravity rises to 30° or 31° Baumé, when it is set aside to crystallise. A good and economical process.
6. Chloride of potassium, 76 parts, and fresh calcium hydrate, 222 parts, are reduced to a thin paste with water, q. s., and a stream of chlorine gas passed through the mixture, to saturation; chloride of calcium and chlorate of potassium are formed; the last is then removed by solution in boiling water, and is crystallised as before. This process, which has received the approval and recommendation of Liebig, has long been practised in Germany, and was originally introduced to this country by Dr Wagenmann. The product is very large, and of excellent quality.
Prop. White, inodorous, four-or six-sided pearly scales, soluble in about 20 parts of cold and 21⁄2 parts of boiling water; in taste it resembles nitre, but is somewhat more austere; at about 450° Fahr. it undergoes the igneous fusion, and on increasing the heat almost to redness effervescence ensues, and fully 39% of pure oxygen gas is given off, whilst the salt becomes changed into chloride of potassium. When mixed with inflammable substances and triturated, heated, or subjected to a smart blow or strong pressure, or moistened with a strong acid, it explodes with great violence.
Pur., Tests, &c. The usual impurity of this salt is chloride of potassium, arising from careless or imperfect manipulation. When this is present, a solution of nitrate of silver gives a curdy white precipitate, soluble in ammonia; whereas a solution of the pure chlorate remains clear.
Uses. Chlorate of potassium is principally used in the manufacture of lucifer matches, fireworks, oxygen gas, &c., and as an oxidising agent in calico printing. It was formerly used to fill percussion caps, but was abandoned for fulminating mercury, on account of its disposition to rust the nipples of the guns. As a medicine it is stimulant and diuretic. It has been given in dropsy, syphilis, scurvy, cholera, typhus, and other depressing affections. It gives a fine artificial colour to the blood.
(Stevens.)—Dose, 5 to 15 gr., in solution, twice or thrice a day.
Concluding Remarks.—Formerly, chlorate of potassium was a salt which was made only on the small scale, and chiefly used in experimental chemistry; now it is in considerable demand, and forms an important article of chemical manufacture. The latter has hence, of late years, received considerable attention and improvement in the leading laboratories of Europe. The chlorate requires to be handled with great care. It should never be kept in admixture with any inflammable substance, more especially with sulphur, phosphorus, or the sulphides, as these compounds are exploded by the most trivial causes, and, not unfrequently, explode spontaneously.
Potassium, Chloride of. KCl. Syn. Chloride of potassa. Prep. The chloride of potassium of commerce is usually a secondary product in the manufacture of chlorate of potassium and other substances. The mother-liquor of the former is evaporated to dryness and heated to dull redness, the calcined mass is then dissolved in water, the solution purified by defecation and evaporated down for crystals.
It can also be well prepared by neutralising boiling solution of carbonate of potassium by dilute hydrochloric acid, evaporating down, and crystallising.