MALIC (ind'Ilk) ACID, An organic substance of which three modifications are theo retically capable of existence. When actually obtained, these three modifications are found to possess the same chemical properties and to differ from one another only in one of their optical properties: viz. the power of rotating the plane of polarized light.
(1) The modification of malic acid that is usually nut with is found widely distributed in the plant-wo•ld. The name malic is derived from the Latin malum, an apple, the acid having been first discovered by Scheele in unripe apples (1785) but the acid occurs also, either in the free state. or combined in the form of salts (mal ales), in gooseberries. currants—in fact. in most acidulous fruits. It may be readily prepared by boiling the expressed juice of unripe mountain ash berries with milk of lime, and dissolving the precipitated neutral calcium salt in hot nitric acid diluted with water; the acid calcium salt thus produced is decomposed with oxalic acid, the precipitated calcium oxalate removed by filtra tion, and the filtrated solution of manic acid evaporated to dryness. In this manner malic acid may he obtained in the form of colorless, deliquescent crystals that melt at 100° C. and are readily soluble in water and in alcohol. The solu tions have the power of turning the plane of polarized light to the left.
(2) The second modification of malic acid may be obtained by the reduction of ordinary tartaric acid. lts solutions have the power of turning the plane of polarized light to the right.
(3) The third modification of malic acid may be prepared by a variety of chemical methods: it has been obtained from mono-hromo-suceinie, fumaric, and malic acids, and from certain other substances. But whatever the way in avhich it is made, it is fi mid, on examination, to be noth ing but an intimate mixture of precisely equal parts of the first two modifications. It is optical ly inactive because its components turn the plane of polarized light in opposite directions and so neutralize each other's rotatory poser. Though cry similar in most of its properties to the ilevo-rotatory modification, it is found to be less soluble in water, to crystallize somewhat more readily, and to form crystals that are not de liquescent. The separation of its components may he effected by the crystallization of their •in•honine salts, which differ from each other considerably in their physical properties.
Chemically, malic acid is a hydroxy-derivative of suceinie acid, into which it is readily eon Vested by the action of hydriodie acid at a high temperature. The chemical relationship of malic and succinie-acids is shown by their constitution al formulas: CH (011) .0001I Millie acid Succinic acid According to the theory of stereo•chemistry ,(q.v.), the existence of three modifications of malic acid is due to the fact that the molecule of the acid contains a carbon atom to which four different atomic groups are linked: viz. II, OH, Co011, and CII,C001i.