Syn. Soluble Tartar.

Preparation and Composition. Soluble tartar is made by saturating the excess of tartaric acid in bitartrate of potassa, by means of carbonate of potassa; the same plan of proceeding precisely being followed as in the preparation of the preceding salt. One equivalent of the bitartrate is thus converted into two of the tartrate, which consists of one equivalent of tartaric acid and one of potassa, without water of crystallization.

Properties

instead of being allowed to crystallize, as directed in the U. S. formula, the solution is generally evaporated to dryness; the salt being stirred towards the close of the process, in order to cause it to granulate. Hence, as found in commerce, tartrate of potassa is almost always in the form of a powder, more or less granular. When crystallized, it has the shape of irregular hexagonal prisms with dihedral summits. in either form, it is white, inodorous, of a saline, bitterish, and very disagreeable taste, very soluble in water, nearly insoluble in alcohol, and deliquescent on exposure to the air. When heated to redness it evolves the odour of caromel, and is converted into carbonate of potassa, which is left behind with charcoal.

Incompatibles. Tartrate of potassa is decomposed by most of the acids and acidulous salts, which reconvert it into the bitartrate by taking half of its base. its solution yields precipitates of insoluble tartrates with the soluble salts of lime, bayrta, and lead.

Medical Properties and Uses

This salt was known in pharmacy about two centuries since, and was formerly more used than at present, having been superseded by others more energetic and less unpleasant. it has the ordinary properties of the saline cathartics, and may be employed for the same purposes. Like Rochelle salt, it has the property, when taken in small and repeated doses, of rendering the urine alkaline. it has also the property of diminishing the griping effect of senna, and has been especially recommended as an addition to the infusion of that cathartic. The dose as an aperient is from one to four drachms, as a purge from half an ounce to an ounce.