water, and the resulting solution, after defecation or filtration, is concentrated by evaporation, so that crystals may form as the liquid cools; these are redissolved in hot water, and the solution allowed to cool very slowly, when large and beautiful yellow crystals of ferrocyanide of potassium are deposited.—Product. 1 ton of dried blood or woollen refuse, with 3 cwt. of pearlash, yields from 2 to 21⁄2 cwt. of commercial ferrocyanide. The mother-liquor contains sulphate of potassium.
Prop. It forms large and very beautiful yellow crystals, which are permanent in the air, and very tough and difficult to powder; it is soluble in 4 parts of cold and 2 parts of boiling water; has a mild saline taste; at a gentle heat loses water; at a higher temperature, in closed vessels, it is for the most part converted into cyanide of potassium, and, when exposed to the air, into cyanate of potassium. Precipitates solutions of antimonous, bismuth, mercurous, and zinc salts, white; cadmium salts, of a pale yellow; cuprous salts, white, turning red; ferrous salts, white, turning blue; lead salts, white; manganous salts, white, turned red; mercuric salts, white, turning bluish; nickelous salts, white, turning green; silver salts, white; stannous salts, white; cobalt salts, green; cupric salts, chocolate red; ferric salts, dark blue; palladous salts, green; stannic salts, yellow; uranic salts, reddish brown; and zinc salts, white.
Uses, &c. Ferrocyanide of potassium is chiefly used in dyeing and calico printing, in the manufacture of Prussian blue, in electro-plating, and, in chemistry, as a test, and a source of hydrocyanic acid. As a medicine it is said to be sedative and astringent, and in large doses purgative, but appears to possess little action.—Dose, 10 gr. to 1⁄2 dr., dissolved in water; in hooping-cough, chronic bronchitis, night-sweats, leucorrhœa, &c. D’Arcet swallowed a solution containing 1⁄2 oz. of this salt without experiencing any injurious effects.
Potassium, Hydrate of. KHO. Syn. Potassa hydrate, Hydrate of potassa, Potassa, Caustic p., Hydrated oxide of potassium; Potassa caustica (B. P.), Potassa (Ph. E.), P. caustica (Ph. D.), P. hydras (Ph. L.), P. fusa. Prep. 1. (Ph. L.) Liquor of potassa, 1 gall.; evaporate the water in a clean iron vessel over the fire until the ebullition being finished, the residuum of potassium hydrate liquefies; pour this into proper moulds.
2. (Ph. E. & D.) As the last, but pouring the fused hydrate upon a bright and clean iron plate (silver or iron dish—Ph. D.); as soon as it solidifies, break it quickly (into fragments), and put it into stoppered glass (green-glass—Ph. D.) bottles.
3. (Pure.) The hydrate, obtained as above, is dissolved in alcohol or rectified spirit, and, after repose for a few days in a closely stopped green-glass or silver vessel, the solution
is decanted, and cautiously evaporated in a deep silver basin, out of contact with the air.
4. (Pure.) M. Polacci states that he procures very pure hydrate of potash in a few minutes by the following process. He heats together in an iron vessel to a red heat a mixture consisting of 1 part of nitrate of potash well triturated with 2 or 3 parts of iron filings. The mass becomes red in a few minutes, and, after cooling, it is treated with water, left to settle, and then decanted. A more or less concentrated solution may thus be obtained, or it may be evaporated to produce the solid potash.
Prop., &c. When perfectly pure it is white, solid, very soluble in water and in alcohol; very deliquescent; intensely acrid and corrosive; and exhibiting the usual signs of alkalinity in the highest degree. That of the shops has usually a greyish or bluish colour.
Potassium, I′odate of. KIO3. Syn. Potassæ iodas. L. Prep. Neutralise a hot solution of hydrate of potassium with iodine, evaporate to dryness by a gentle heat, powder the residuum, and digest it in alcohol, to remove iodide of potassium, dissolve the insoluble portion in hot water, and crystallise.