478 



posed by Kuhlmann, Berzelius and others for the preparation of the 

 so-called xanthine, and in that of Rochleder for the preparation of 

 his ruberythric acid, all of which depend on the use of alkaline earths 

 or basic acetate of lead, products of decomposition of rubian must in 

 every case be formed. Besides the substances just mentioned, a 

 little acetic acid, and sometimes also rubiadine, and sugar in small 

 quantities are formed. Whether the first is an essential product of 

 decomposition or not, the author leaves undecided ; but the other two 

 he considers as decidedly secondary products, resulting from the 

 decomposition of rubidehydran or rubihydran. 



Rubianic acid is soluble in water and alcohol, but not in ether. 

 It crystallises in lemon-yellow silky needles. Its watery solution 

 has a distinctly but not strongly bitter taste. When heated it yields 

 a sublimate of alizarine. By the action of strong acids, as well as 

 of caustic alkalies and of erythrozym, it is decomposed into alizarine 

 and sugar. Its compounds with potash and ammonia crystallize in 

 small puce-coloured needles. The soda salt is deposited from the 

 watery solution as a mass of small red spherical grains, which are 

 very sparingly soluble in water. These compounds possess very 

 little stability. The baryta and lime salts are obtained by double 

 decomposition as red precipitates. The acid is completely precipi- 

 tated from its watery solution by basic acetate of lead, the precipi- 

 tate being red, and resembling that produced by the same salt in a 

 solution of rubian. 



The composition of rubianic acid is expressed by the formula 



^52 ^29 ^27. 



that of the potash salt by 



^52 H 28 ^26 + K O, 



that of the neutral baryta salt by 



C 52 H 28 0^ + BaO + HO. 



The conversion of the acid into alizarine and sugar is symbolized by 

 the following equation : 



C 52 H 29 27 +5HO=2C 14 H 6 4 +2C 12 H 12 12 . 

 In order to leave no doubt regarding the correctness of the formula, 

 the author determined the quantity of alizarine formed by the decom- 

 position of the acid. According to calculation, 100 parts of acid 

 should yield 43 '44 parts of dry alizarine. In two experiments the 

 author obtained 42-47 and 45' 17 per cent, of alizarine. 



