TARTARIC acid, in chemistry, was procured by Scheele in a separate state in the year 1770. The process which he followed was by boiling a quantity of the substance called tartar, or cream of tartar, in water, and adding powdered chalk till; effervescence ceased, and the liquid no longer reddened vegetable blues. It was then allowed to cool, the liquor fil tered, and a white insoluble powder re• mained on the filter, which was carefully removed and well washed. This was put into a matrass, and a quantity of sulphu ric acid, equal in weight to the chalk em ployed, diluted with water, poured upon it. The mixture was allowed to digest for twelve hours on a sand bath, stirring it occasionally with a glass rod. The sul phuric acid combined with the lime, and formed a sulphate of lime, which fell to the bottom. The liquid contained the tartaric acid dissolved in it. This was decanted off, and a little acetate of lead dropped into it, as a test to detect the sulphuric acid, should any remain; and if this be the case, it must be digested again With more tartrate of lime, to car ry off what remains of the sulphuric acid. It is then to be evaporated, and about one-third of the weight of the tar tar employed is obtained of concrete tar taric acid. To purify this, the crystals may be dissolved in distilled water, and again evaporated and crystallized. It seems probable' that this acid exists in a state of purity in some vegetables. Vau quelin found a 64th part in the pulp of the tamarind. Tartaric (or tartarous) acid thus obtained, is in the form of very fine needle-shaped crystals ; but they have been differently described by dif ferent chemists. According to Bergman, they are in the form of small plates, at tached by one extremity, and diverging at the other. They have been foundby others
grouped together in the shape of needles, pyramids, regular six-sided prisms, and square and small rhomboidal plates. The specific gravity is 1.6. This acid has a very sharp, pungent taste ; diluted with water, it resembles the taste of lemon. juice ; and it reddens strongly blue vege-. table colours. When it is exposed to heat, on burning coals, it melts, blackens, emits fumes, froths up, and exhales a sharp pungent vapour. It then burns with a blue flame, and leaves behind a spongy mass of charcoal, in which some of lime have been detected. In the de composition of the tartaric acid by heat, one of the most remarkable products which particularly characterizes it, is art acid liquor of a reddish colour, which amounts to one-fourth of the weight of the former. This was formerly known by the name of pyrotartarous acid. It has a slightly acid taste, produces a dis agreeable sensation on the tongue, is strongly empyreumatic, and reddens the tincture of turnsole. But it has been found, by the experiments of Fourcroy and Vauquelin, to be the acetic acid im pregnated with an oil. Tartaric acid is very soluble in water. The specific gravity of a solution formed by Bergman, was found to be 1.2. This solution in wa ter is not liable to spontaneous decompo sit ion, unless it is diluted. While it is con centrated, it loses nothing of its acid na ture or its other properties. According to the analysis of Fourcroy and Vauque lin, 100 parts of this acid are composed of Oxygen 70 5 Carbon 19 0 Hydrogen . . . 10.5 100.0 Tartaric acid is not applied to any use, and but few of its combinations are em ployed in the practice of medicine.