4184. Chlorate of Potassa

4184.    Chlorate of Potassa. Transmit chlorine gas through a moderately strong and warm solution of pure caustic potassa, or its carbonate, until the alkali be completely neutralized, then boil for a few minutes, gently evaporate until a pellicle forms on the surface, and set it aside, where it will cool very slowly. Crystals of the chlorate will form as the liquor cools, and must be collected, carefully washed with a little ice-cold water, and purified by re-solution and crystallization; the product is pure chlorate of potassa. The mother liquor, which contains much chloride potassium, by evaporation will yield more crystals, less pure than the former, or it may be saved for a future operation. This salt crystallizes in four and six-sided pearly scales; dissolves in 16 parts of water at 60°, and in 21/2 parts at 212°. At about 450° it undergoes the igneous fusion, and on increasing the heat almost to redness, effervescence ensues, and fully 39 per cent, of pure oxygen gas is given off and the residue becomes changed into chloride of potassium. When mixed with inflammable substances, and triturated, heated, or subjected to a smart blow, it explodes with great violence. It also fulminates when thrown into strong acids. (See No. 2124 (Caution in the Use of Chlorate of Potassa).) (Cooley.)

4185. Perchlorate of Potassa

4185.     Perchlorate of Potassa. To concentrated sulphuric acid, gently warmed in an open vessel, add, in small portions at a time, an equal weight of well-dried and finely powered chloride of potassa. The bisulphate of potassa formed, is washed off with a little cold water, and the remaining perchloride of potassa dissolved in boiling water and crystallized.

4186. Chromate of Potassa

4186.     Chromate of Potassa. The yellow chromate of potash of commerce is only prepared on the large scale from the crude chrome ore, and is the common source of nearly all the other compounds of chromium. The ore, freed as much as possible from its impurities, is ground to powder in a mill, and mixed with 1/2 or 1/8 of its weight of bruised nitre, and in this state exposed to a powerful heat for several hours, on tho hearth of a reverberatory furnace, during which time it is frequently stirred up with iron rods. The calcined matter is next raked out and lixiviated with hot water. A beautiful yellow-colored solution results, which is evaporated briskly over a naked fire, when the chromate of potash falls down under the form of a granular yellow salt, which is removed from time to time with a ladle, and thrown into a wooden vessel, furnished with a bottom full of holes, called the draining box, where it is left to drain and dry. In this state it forms the commercial chromate of potash. By a second solution and crystallization, it may be obtained in larger and more regular crystals. (Cooley.)

4187. Bichromate of Potassa

4187.     Bichromate of Potassa. The red chromate of potash is obtained from a concentrated solution of the yellow chromate, by adding sulphuric (or, still better, acetic) acid in quantity equal to half that required for the neutralization of the salt. (See No. 83.) The liquid is then concentrated by evaporation, and slowly cooled, so that crystals may form.