Tartaric acid , also dihydroxy-succinic acid, organic acid of formula C4H6O6, found in many plants and known to the early Greeks and Romans as tartar, the acid potassium salt derived as a deposit from fermented grape juice. The acid was first isolated in 1769 by the Swedish chemist Carl Wilhelm Scheele, who boiled tartar with chalk and decomposed the product with sulfuric acid. Fermentation of the juices of grapes, tamarinds, pineapples, and mulberries produces, on the inner surface of the container, a white crust of potassium acid tartrate known as argol, or lees. Argol, boiled with dilute hydrochloric acid, precipitates as calcium tartrate when calcium hydroxide is added. Upon addition of dilute sulfuric acid, dextrotartaric acid is liberated, which rotates the plane of polarized light to the right. Dextrotartaric acid has a m.p. of 170 (338oF) and is extremely soluble in water and alcohol and insoluble in ether.
Another variety, called levotartaric acid, is identical to dextrotartaric acid except that it rotates the plane of polarized light to the left. This acid was first prepared from its sodium ammonium salt by the French chemist Louis Pasteur. Tartaric acid synthesized in the laboratory is a mixture of equal amounts of the dextro and levo acids, and this mixture, called also racemic tartaric acid, does not affect the plane of polarized light. A fourth variety, mesotartaric acid, also without effect on the plane of polarized light, is said to be internally compensated.
Tartaric acid, in either the dextrorotary or racemic form, is used as a flavoring in foods and beverages. It is used also in photography, in tanning, and as potassium sodium tartrate , also known as Rochelle salt, as a mild laxative. Potassium hydrogen tartrate, also called cream of tartar, is a pure form of argol that is used in baking powders and in various treatments of metals. Antimony potassium tartrate, also called Tartar emetic, Antimony potassium tartarate, also known as Tartar emetic, is used as snail fever-resistant drugs in the pharmaceutical industry, and in treatments of metals.