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 tartari 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 tartari, 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, trans-parent, 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 wool-dyeing, with powdered chalk and alum for cleaning silver, and for the preparation of effervescing drinks and baking-powder . In medicine as potassii tariras 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(C4H406), or Rochelle salt . Tartar emetic (potassium antimonyl tartrate) K . (SbO) C4H406•1H2O . 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 (q.v.) 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 .