MALIC ACID 2110) was discovered in 1785 by Scheele. It received its name from having been first obtained from the juice of apples, in which it exists in considerable quantity, and also, as has been since ascertained, in various other fruits, as cherries, raspberries, strawberries, in house-leek, and the berries of the sorbus or mountain ash. Mr. Donovan, who procured it from the last mentioned source, obtained it of so great purity that he supposed it to be a new and peculiar acid, which he called sorbic acid; but it has since been proved to be identical with the malie. A mucilaginous substance which ac5ompanies the acid obtained from apples prevents its properties from being perfectly and readily developed.
Various processes have been proposed for procuring this acid, and they are generally complicated : the following, proposed by Liebig, is perhaps as good as any : Add carbonate of lime, but not to perfect saturation, to the expressed juice of the mountain ash ; the solution is to be decomposed by nitrate of lead, which precipitates malate of lead ; this, after washing with cold water, is to be heated with boiling dilute sulphuric acid, and the resulting mass with sulphide of barium, by which there are formed sulphide of lead and sulphate of baryta, while the clear liquor contains malic acid, to which ammonia is then added to convert it into bimalate of ammonia, which readily crystallises ; this salt is to be precipitated by acetate of lead, and the resulting malate of load decomposed by hydrosulphuric acid ; the clear liquor, separated from the sulphide of lead, being evaporated by a gentle heat, yields crystals of malie acid, which are not however regular iu their form. Malic acid is colourless, inodorous, very sour to the taste, and acts strongly on vegetable blues ; in a moist air it is deliquescent ; it is very soluble both in water and alcohol. Nitric acid converts it into oxalic acid. Its saline compounds are called malates, some of which exist in nature, as for example, bimalate of lime in the juice of the houseleek.
When malic acid is subjected to a heat of about 350° Fahr., it is de composed into water and two isomeric pyro-acids, the maleic and the fumaric acids.
The malates are not an important class of salts. We shall mention the general properties of a few of them. They may be divided into two classes, namely :—the neutral malates which have the formula C,H,0„ 2M0, and the bimalates consisting of MO HO.
Malate of ammonia is a deliquescent salt, but the bimalate is crystal lisable, unalterable in the air, and insoluble in alcohol. Malate of
potash is a deliquescent mass ; the bimalate forms crystals which are unalterable in the air and insoluble in alcohol. Malate of soda is a deliquescent mass, the supermalate crystallises. Malate of lime is spa ringly soluble in water, requiring 147 parts of it cold, and 85 when boiling : the hot solution deposits crystalline rains on cooling. It is stated to be more soluble in some saline solutions than in pure water ; the bimalate occurs in houseleek and some varieties of sedum; it may be formed by adding acid to the neutral salt; by exposure to heat it dries as a transparent varnish, which distinguishes it from other salts of lime and vegetable acids. It is soluble in water, but insoluble in alcohol. Malate of magnesia yields crystals which are unalterable in the air and are soluble in twenty-eight parts of water ; with excess of acid, a gummy deliquescent saline mass is formed. Malate of baryta both neutral and acidulous, is soluble and gummy; an insoluble subsalt may also be formed. Malate of strontia is gummy and deliquescent, the acid salt is but slightly soluble, but more so in hot than in cold water; the hot volution deposits crystals on cooling. Of the metallic malates we shall state the properties of a few :—Zinc forms three different com pounds with this acid : the neutral malate crystallises in short four sided prisms ; it is soluble in 55 parts of cold water ; by boiling water it is decomposed into a supersalt which dissolves, and a subsalt which is precipitated ; bimalate of zinc crystallises in large regular octoheclrons ; the submalate is an insoluble white powder. Malate of peroxide of iron is a reddish brown-coloured deliquescent mass soluble both in water and alcohol. Malate of copper. whether neutral or acidulous, dries so as to form a green varnish which is unalterable in the air. The malate of silver is a gummy mass, but the bimalate is a crystal lisable salt, which readily separates as such from solution in water. Malate of lead is nearly insoluble in cold water, but dissolves in boiling water, and the solution on cooling deposits brilliant white crystalline scales of this salt.
Malic acid forms two amides, namely, Matamic acid isomeric with aspartic acid, and malamide isome ric with asparagin. [AssAnsorsr.] The following compounds are closely related to these amides ;