Tartar, the name commonly applied to crude acid potassium tartrate or "bitartrate of potash," HK(C4H406). During the process of fermentation wines deposit a crystalline crust of argol; this, after being roughly purified by recrystallization, is known as tartar, and when further purified and freed from colouring matters becomes "cream of tartar," also called technically "cream." With the iatrochemists tartar was a generic term which included both this tartarus vini and various substances obtained from it, and even salts, such as salt of sorrel (potassium oxalate), that resembled it. Thus sal fixum tartari was potassium carbonate, which on exposure to the air deliquesces to oleum tartan per deliquium; neutral potassium tartrate was called tartarus tartarisatus, because it was prepared by neutralizing ordinary tartar with the sal fixum; tartarus chalybeatus was a preparation with iron; and spiritus tartan, used by Paracelsus, was prepared by dry distillation of tartar. Paracelsus also used the term in a still wider sense to signify abnormal precipitates or sediments deposited from animal secretions; the same idea is apparent in the popular application of the word to the salivary calculus which forms on the teeth.
Cream of tartar is prepared by dissolving granulated argol in boiling water and allowing the solution to stand. The clear liquid is then drawn off and crystallized. The slightly coloured crystals thus obtained are redissolved in hot water, the colouring matters got rid of by means of pipeclay or egg-albumen, and the solution filtered and crystallized, the name "crean of tartar" being originally applied to the crust of minute crystals that form on its surface as it cools. The salt crystallizes in masses of small, hard, colourless, transparent, rhombic prisms. It is precipitated when an excess of a potassium salt is added to a solution of tartaric acid, but it dissolves in mineral acids, and in alkalis and alkaline carbonates. Solutions of boric acid or borax dissolve it freely, forming soluble cream of tartar, which is a white powder permanent in the air when made with the acid, but deliquescent when borax is employed. Its slight solubility in alcohol explains why it is deposited by wines as they mature. One part by weight of the salt dissolves in 15 parts of boiling water, but at lower temperatures the solubility is greatly diminished, and at o° C. about 416 parts of water are required. When heated it is decomposed with formation of potassium carbonate and carbon, inflammable gases having an odour of burnt bread being evolved. The salt is used for the manufacture of tartaric acid; it is also employed in the mordant bath for wooldyeing, with powdered chalk and alum for cleaning silver, and for the preparation of effervescing drinks and baking-powder. In medicine as potassii tartras acidus it is of some slight importance as a diuretic and purgative. The more soluble normal salt, K2(C4H406), is used for the same purposes; it is formed by dissolving powdered cream of tartar in a hot solution of potassium carbonate. If sodium carbonate is substituted the result is KNa(C 4 H 4 O 6), or Rochelle salt.
Tartar emetic (potassium antimonyl tartrate)K. (SbO) C4H406 ZH20. This substance has been known for a long period, being mentioned by Basil Valentine. It may be prepared by warming 3 parts of antimonious oxide with 4 parts of cream of tartar, in the presence of water, replacing the water as it evaporates; after digestion is complete, the solution is filtered hot. Powder of algaroth may be used in place of the antimony oxide. Tartar emetic crystallizes in small octahedra, which lose their water of crystallization gradually on exposure to air, and become opaque. It is soluble in 14.5 parts of cold water and 1.9 parts of hot, the solution showing an acid reaction to litmus. It possesses a nauseous metallic taste and produces vomiting when taken internally, whilst in large doses it is poisonous. It is used medicinally, and also as a mordant in dyeing and calico-printing.
