The American Cyclopædia (1879)/Kinic Acid

KINIC ACID, also called cinchonic and quinic acid, a substance obtained in combination with lime in evaporating the infusion of Peruvian bark to a solid consistence, and treating the extract with alcohol. If an aqueous decoction of cinchona bark be mixed with milk of lime until it assumes a feebly alkaline reaction, the vegetable bases and the tannic acid are precipitated, and calcic quinate remains in the liquid; this salt may be crystallized from the mother liquor by evaporation, and decomposed by the cautious addition of oxalic or of sulphuric acid. The kinic acid may then be obtained in crystals from the solution in the form of transparent, colorless, rhomboidal plates. These have a sour taste, and readily dissolve in water or alcohol. Their composition is expressed by the formula H,C₇H₁₁O₆. By combining the acid with cinchonia or quinine it is restored to the saline condition in which it existed in the bark, and may thus be applied in medicine in concentrated form more nearly representing the peculiar character of the bark than in the ordinary combinations of the alkaloid with sulphuric or other mineral acid, although the therapeutic advantage of such a combination is by no means proved. Kinic acid by its presence serves to distinguish genuine barks. The method of testing is to boil ¼ oz. of bark with a little lime, and, after pouring off and concentrating the liquor, to commence distilling it in a retort with a mixture of half its weight of sulphuric acid and peroxide of manganese. If kinic acid is present, a volatile substance called kinone or chinone, of yellow color and peculiar odor, the vapor of which is very irritating to the eyes, comes over with the first portions, and is instantly recognized. The spurious barks having no kinic acid do not afford kinone. It has been ascertained that caffeic acid also yields kinone when treated in the manner above decribed. Kinic acid is said to have been found in the leaves of vaccinium myrtillus. It is onverted in the system into hippuric acid.