Synonym. Potassae Bitartras.

Prep. From argol, the deposit which occurs on the inside of wine-casks, by purification with charcoal and clay. It is called cream of tartar, from the purest crystals being skimmed off the saturated solution while evaporating.

Prop. & Comp. Cream of tartar occurs as a very fine, gritty, white powder: or in fragments of cakes crystallized on one surface; or in small oblique rhombic prisms; acid, slightly soluble in water; but insoluble in spirit. Composition (HO, KO, C8 H4 O10). Heated in a crucible, it evolves inflammable gas and the odour of burned sugar, and leaves a black residue (carbonate of potash and carbon), which effervesces with dilute hydrochloric acid, and forms a solution which, when filtered gives a yellow precipitate with bichloride of platinum, and when neutralised by ammonia is rendered slightly turbid by oxalic acid: 188 grains, heated to redness till gas ceases to be evolved, leave an alkaline residue, which requires for exact saturation 100 measures of the volumetric solution of oxalic acid, equivalent to 47 grains of potash.

Off. Prep. Contained in Pulv. Jalapae Comp., and Confectio Sulphuris.

Therapeutics. In small doses, refrigerant and somewhat diuretic; in larger doses, a powerful hydragogue purgative, without producing much depression. Employed to form an acid drink in febrile and dropsical affections, and as a purgative in dropsies, depending upon renal or cardiac disease.

Dose. As a refrigerant or diuretic, 20 gr. to 60 gr.; and as a hydragogue purgative, 120 gr. to 300 gr.

Adulteration. Often contains a little tartrate of lime.