232 ACIDS. 



For the separation of malic acid, see § 214. 



§ 221. Fvmaric acid can also be sublimed, and, like oxalic and 

 succinic acids, yields a precipitate with acetate of lead that 

 gradually assumes a crystalline condition (§§81, 214). It 

 differs from malic acid in its slight solubility in water (according 

 to Lassaigne about 1 in 260 at 17°). It is much more easily 

 soluble in hot water, arid is also dissolved by ether and by cold 

 spirit. The solubility of the silver-salt is extremely slight ; 

 manganous fumarate is also sparingly soluble in water, but freely 

 in spirit. The acid potassium and acid ammonium salts are not 

 very soluble in water,. and scarcely at all in cold 80 per' cent, 

 spirit. Lime-water does not precipitate f umaric acid. 



MaJeic acid is isomeric with the preceding, and, like it, is op- 

 tically inactive arid yields a ciystalline lead-salt. It is freely 

 soluble in water, but cannot be sublimed without decomposition. 



Kinic acid may also be mentioned here. It is precipitated by 

 ammoniacal, but not by normal acetate of lead ; and when 

 saturated with mUk of lime, yields at first a calcium-s^lt soluble 

 in water. 



Many other vegetable acids can be separated from Mnic acid 

 by precipitation with normal acetate of lead ; the filtrate, after 

 removal of the excess of lead as sulphide, can be freed from 

 sulphuretted hydrogen, boiled with milk of lime, concentrated, 

 and allowed to stand, when a crystalline deposit of kinate of 

 calcium will gradually separate, or more rapidly if spirit is added. 

 The presence of kinic acid in the deposit may be demonstrated 

 hy heating with sulphuric acid and black oxide of manganese ; 

 the quinone thus ■ ptoduced is volatile, crystallizes in yellow 

 needles, and can be detected even in traces by its iodine-like 

 odour (§167, arbutin). 



Kinic acid and its silver-salt are easily soluble in water. ^ 



§ 222. Lactic Acid. — Although the occurrence of lactic acid in 

 living plants has not been placed beyond doubt, we must devote 

 a few lines to it here, as it is. frequently produced from carbo- 

 hydrates when vegetable infusions are allowed to stand, and is 

 therefore ofteri met with in plant-analysis. It can be detected by 



' For rvbichloric acid, which occasionally accojnpatiies kinic acid and, like 

 it, is only precipitated by alkaline acetate of lead solution, see Schwarz; 

 Sitzungsber. d. Akad. d. W. in Wien Math. nat. CI. 26, 1852. Kubichloric 

 acid is decomposed with simultaneous separation of green insoluble chlorrubin 

 when its aqueous solution is boiled with dilute hydrochloric acid. 



