Potassium, Borate of. K4B4O8. Syn. Potassæ boras, L. Prep. From dry carbonate of potassium and dry boracic acids, equal parts, reduced to powder, and heated to redness in a covered crucible; the sublimed mass, when cold, being dissolved in boiling water, and the filtered solution concentrated by evaporation, and then set aside to crystallise; or at once completely evaporated to dryness.—Dose, 1 to 6 gr.; in calculi, &c.
Potassium, Borotartrate of. Syn. Potassæ borotartras, Cremor tartari solubilis, L.; Crème de tartre soluble, Fr. Prep. (P. Cod.) Crystallised boracic acid, 1 part; bitartrate of potassium, 4 parts; water, 24 parts; dissolve, by the aid of heat, in a silver basin, and, constantly stirring, evaporate the resulting solution, either to dryness, and then powder it, or merely to a syrupy consistence, when it may be spread upon plates, and dried in scales, by the heat of a stove. It must afterwards be preserved from the air.
Prop., &c. A white, deliquescent powder, freely soluble in water. It has been used as a solvent for lithic calculi, and in gout, &c.—Dose, 15 to 30 gr. In doses of 2 to 3 dr. it is laxative, and is very popular as such on the Continent.
Potassium, Bromide of. KBr. Syn. Potassii bromidum (B. P.). Prep. Exactly as the iodide, which it resembles in its character, only being somewhat less soluble in water and more in alcohol. Employed in similar cases and given in similar doses to the iodide.
Potassium, Carbonate of. K2CO3. Syn. Carbonate of potassa, Subcarbonate of potassa, Salt of tartar; Potassæ carbonas (B. P., Ph. L., E., D.). Impure or crude carbonate of potassium is chiefly imported from America and Russia, and is obtained by lixiviating wood ashes, and evaporating the solution to dryness. The mass is then transferred into iron pots, and is kept in a state of fusion for several hours, until it becomes quiescent, when the heat is withdrawn, and the whole is left to cool. It is next broken up and packed in air-tight barrels, and in this state constitutes the ‘potashes’ or ‘potash’ of commerce. Another method is to transfer the black salts, or product of the first evaporation, from the kettles to a large oven or furnace, so constructed that the flame is made to play over the alkaline mass, which is kept constantly stirred by means of an iron rod. The ignition is continued until the impurities are burned out, and the mass changes from a blackish tint to a dirty or bluish white. The whole is next allowed to cool, and is then broken into fragments, and packed in casks as before. It now constitutes ‘pearlash.’
When pearlash is dissolved in cold distilled water, the solution depurated, filtered and crystallised,
or simply evaporated to dryness, it forms ‘refined ashes,’ or carbonate of potash sufficiently pure for most pharmaceutical and technical purposes. The granulated carbonate of potash, salt of tartar, or prepared kali, of the shops, is simply refined ashes which, during the evaporation, and more especially towards the conclusion of the desiccation, has been assiduously stirred, so that it may form small white granulations, instead of adhering together to form an amorphous solid mass. In this state it constitutes the ordinary or carbonate of potassa of the Pharmacopœias. Ordinary potash or pearlash may be refined as follows:—Raw potash, 10 parts, is dissolved in cold water, 6 parts, and the solution is allowed to remain for 24 hours, in a cool place; it is then filtered, and somewhat concentrated by evaporation, crystallisation being prevented by continually stirring the mass until the whole is nearly cold; it is next decanted into a strainer, and the mother-liquor allowed to drip off; the residuum is evaporated to dryness at a gentle heat, and redissolved in an equal quantity of cold distilled water; the new solution, after filtration, is again evaporated to dryness. The product is quite free from potassium sulphate, and is nearly free from both potassium chloride and silicates.
Potassium, Pure Carbonate of. Carbonate of potassa (Potassæ carbonas purum—Ph. E. & D., and Ph. L., 1836).—(Ph. L., 1836.) From bicarbonate of potassium, in crystals, heated to redness in a crucible.
(Ph. E.) As the last. Or, more cheaply, by dissolving bitartrate of potassium in thirty parts of boiling water, separating and washing the crystals which form on cooling, heating them in a loosely covered crucible to redness as long as fumes are discharged, breaking down the mass, and roasting it in an oven for two hours, with occasional stirring; lixiviating the product with (cold) distilled water, filtering the solution thus obtained, evaporating it to dryness, granulating the salt towards the close by brisk agitation; and, lastly, heating the granular salt thus obtained nearly to redness.
(Ph. D.) Bitartrate of potassium, 2 lbs., is exposed to a red heat in an iron crucible, as before; the powdered calcined mass is boiled for 20 minutes in water, 1 quart, the solution filtered, and the filtrate washed with water, 1 pint, to which ammonium sesquicarbonate, 1⁄2 oz., has been added; the mixed and filtered liquors are evaporated to dryness, and, a low red heat having been applied, the residuum is rapidly reduced to powder in a warm mortar, and at once enclosed in (dry and) well-stoppered bottles.