Cream Of Tartar, a bitartrate of potassa purified from the crude tartar or argol, which collects in a crystalline deposit upon the bottom and sides of wine casks during the fermentation of the wine. Its chemical composition is: tartaric acid 2 equivalents, = 132; potassa 1, = 47.2; and water 1, = 9. As the saccharine matters which hold the tartar in solution are converted into alcohol, the salt is precipitated in a crude state, together with some tartrate of lime and the coloring matter of the wine. Red wines give a red color to the crude article. When the crude salt is dissolved in boiling water, and this is allowed to cool, crystals of the cream of tartar are deposited and form a crust on the bottom of the vessel, cold water holding in solution only 1/184 of its weight of the salt, and boiling water 1/18. The crust is redissolved in boiling water, and 4 or 5 per cent, of pipe clay is added. On evaporating the solution, the clay precipitates with the coloring matter, and the salt of tartar is deposited in white crystals. These are bleached by being spread upon cloths for some days and dried, and then constitute the cream of tartar of commerce. It is usually sold as a powder, and in this state is liable to have been mixed with various adulterants, as chalk, clay, gypsum, sand, flour, etc.
It is therefore better to purchase it in the crystalline form in which it is received from the French manufacturers. It is, however, never pure, always containing a small percentage of tartrate of lime. - Cream of tartar is used in medicine as a diuretic, refrigerant laxative, and cathartic. In the dose of 40 grs. or less, largely diluted with water, and repeated several times a day, it is a diuretic and moderate refrigerant. In the dose of about two drachms it is a laxative, and in the dose of half an ounce it acts as a cathartic, producing watery discharges. Combined with digitalis and squill, it is often advantageously prescribed in dropsical affections. It is used as a refrigerant drink in many febrile conditions. Its laxative action is useful in piles and prolapsus ani. As a purge (generally combined with jalap) it often does good service in inflammation, and especially in inflammatory dropsy. Its tendency is to render the urine alkaline, though it is less powerful in this direction than the more soluble salts of the alkalies combined with vegetable acids.
A refreshing beverage called imperial is prepared by dissolving half an ounce in three pints of boiling water, and adding four ounces of white sugar and half an ounce of fresh lemon peel. - Cream of tartar and tartrate of antimony compose the medicine tartar emetic. Rochelle salt is prepared by adding cream of tartar to carbonate of soda, by which a tartrate of potassa and soda is produced. When decomposed by heat, cream of tartar is converted into a pure carbonate of potassa. Mixed with half its weight of nitrate of potash and deflagrated, it forms the flux called black flux, used for crucible assays. White flux is prepared with two parts of nitre to one of cream of tartar. In making bread, cream of tartar is often usefully employed, mixed with half its weight of carbonate of soda. The excess of acid produces slow effervescence, and the escape of carbonic acid gas, distending the dough, causes it to rise.
See Cream of Tartar.