176 XANTHIN. 



and 1400 at 100. Insoluble in alcohol and in ether, it dissolves 

 readily in dilute acids and alkalis (characteristically in ammonia) 

 forming crystallisable compounds. 



Reactions. The discrimination of members of the xanthin 

 group is not easy, since from their close relationship they yield 

 many reactions in common. The following are characteristic of 

 xanthin. 



i. WeideVs reaction. 1 The substance is warmed with freshly 

 prepared chlorine-water and a trace of nitric acid as long as any 

 gas is evolved : it is then carefully evaporated to dryness and, if 

 xanthin is present, the residue turns pink or purplish-red on the 

 access of ammonia fumes. Carnin gives a similar colouration if 

 but little chlorine-water is used, while guanin and adenin do 

 not. 



ii. Hoppe-Seyler's reaction. When xanthin is introduced into 

 some caustic soda with which some chloride of lime has been 

 mixed, each particle of the substance surrounds itself with a dark 

 green ring which speedily turns brown and then disappears. 



FIG. 25. CRYSTALS OF XANTHIK SILVER-NITRATE, C 5 H 4 N 4 O 2 . AgNO 3 . 

 (Krukenberg after Kiihne.) 



iii. Strecker's test? When evaporated to dryness on porcelain 

 with nitric acid a yellow residue is obtained which turns reddish- 

 yellow on the addition of caustic soda or potash (not of ammonia), 

 and reddish-violet on subsequent warming. Distinctive from 

 uric acid. 



iv. Xanthin is more readily soluble in ammonia than is uric 

 acid. 



v. Xanthin yields in solution in dilute nitric acid a character- 

 istic crystalline compound with nitrate of silver, which differs 

 from the similar compound of hypoxanthin both in the forms 

 which it presents and in its greater solubility in nitric acid of sp. 

 gr. 1-1 at 100. It is therefore used as a means of separating 

 xanthin and hypoxanthin. 



1 Ann. d. Chem. u. Pharm. Bd. CLVIII. (1871), S. 365. This reaction was given 

 by its author for hvpoxanthin, but apparently in error. Cf. Kossel, Zt. f. phi/siol. 

 Chem. Bd. vi. (1882), S. 426. Salomon, Ber. d. d. chem. Gesetl. 1883, S. 198. 



- Ann. d. Chem. u. Pharm. Bd. cvm. (1858), S. 146. 



