"Take of impure supertartrate of potassa, any quantity. Wrap it up in moist bibulous paper, or put it into a crucible; and, having placed it among live coals, let it be burnt to a black mass; which, after having reduced it to powder, expose in an open crucible to a moderate fire, until it become white, or at least ash-coloured, taking care that it be not melted. Then dissolve it in warm water; strain the solution through a linen cloth, and evaporate it in a clean iron vessel, stirring constantly towards the end of the process with an iron spoon, lest any of it should adhere to the bottom of the vessel. A very white salt will remain, which is to be left a little longer on the fire, till the bottom of the vessel become red-hot. Finally, when it is cold, let it be preserved in well-stopped glass vessels."

1 Nicholson's Journal, 4to. iii, 215.

Potassae Carbonas e Tartari Crystallis, Dub. Carbonate of Potassa from Crystals of Tartar.

"Take of crystals of tartar, any quantity. Heat it to redness in a silver crucible lightly covered, until fumes cease to be emitted. Let the residue be reduced to a coarse powder, and in the same crucible, left uncovered, roast it for two hours, stirring it frequently. Then boil it in twice its weight of water, during a quarter of an hour; and after due subsidence of the impurities, pour off the pure solution. Let this part of the process be three times repeated. Filter the mixed leys, and evaporate them in a silver vessel; then, while the residuary salt is drying, granulate it by brisk agitation, and expose it to an obscure red heat. Take it out of the vessel before it be quite cold, and let it be preserved in well-stopped vials."

Syn. Soucarbonate de Potasse (F.), Sotto-carbonato di Potassa (I.).

The product of all of these processes is a carbonate of potassa. The degree of heat to which the crude bitartrate is exposed decomposes its tartaric acid; and by the re-union of two of its components, oxygen and carbon, carbonic acid is formed, which combines with the potassa, while the remaining carbonaceous matter produced by the decomposition is burnt out by the subsequent roasting. The resulting saline mass, besides carbonate of potassa, contains also a small portion of carbonate of lime and some argil, which, however, are separated by the solution and filtration.

Qualities. - These are in every respect the same as those of the salt obtained from the potashes of commerce; it, however, contains fewer impurities. Its constituents, according to Berard, are 29.79 acid, and 70.21 alkali in water, in 100 parts.1 When well prepared, its constituents are, 1 eq. of carbonic acid=22.12+1 potassa=47.15 + 2 waters 18 = 87.27.

(K-C + H2).

Carbonate of potassa is often adulterated, or very carelessly prepared. If one part of it be dissolved in eight parts of distilled water, and saturated with pure nitric acid, the presence of silicious earth will be indicated by the solution becoming turbid; and, by weighing the precipitate, its quantity may be ascertained. A precipitate being formed on the addition of chloride of barium, indicates the presence of sulphates; a white precipitate turning bluish on exposure to the light, on adding nitrate of silver, proves the presence of hydrochlorates; calcareous earth is rendered evident by dropping into a solution a few drops of a solution of oxalic acid or oxalate of ammonia; and silica by heating the saturated hydrochlorate to redness, and lixiviating: the silica remains undissolved. It is incompatible with acids and acidulous salts, hydrochlorate of ammonia, acetate of ammonia, sulphates, the salts of calcium, lime-water, and metallic salts.

1 Annales de Chimie, lxxi. 55.

Medical properties and uses. - Carbonate of potassa is de-obstruent, diuretic, and antacid. In small doses, it is sometimes given in cases of glandular obstructions of the abdominal viscera, particularly hepatic obstructions, with seeming advantage; but it is not certain that the benefit does not arise from the effects of the remedy in correcting acidity of the primae viae. As an antacid it is useful in dyspepsia and gout. Its effects on the kidneys are considerable, when aided by plentiful dilution, and it passes through these organs without being decomposed. The dose as an antacid is from gr. x. to 3ss. The principal use, however, of this salt in medicine is for the formation of saline draughts, for which purpose it is given in combination with a solution of the citric acid, or with recent lemon juice, in the proportion of Эj. of the salt of f 3 iv. of the lemon juice, or of an acid solution, containing gr. xviii. of citric acid, in febrile affections. When given as an antacid, its taste and acrimony are most perfectly covered by milk.

Officinal preparations. - Aqua Supercarbonatis Potassae, E. Po-tassae Acetas, L. E. D. Potassae Carbonas, L. Potassae Tartras, L. E. D. Liquor Potassae, L. E. D. Liquor Potassae Carbonatis, L. D. Sulphas Potassae, E. Magnesia Carbonas, L. D. Potassae Sulphuretum, L. E. D. Mistura Ferri composita, L. Pilulae Ferri compositae, L. Liquor Potassae arsenitis, L. Sulphur anti-moniatum fuscum, D. Alcohol, L.