CHAP. IX.] THE CONTRACTILE TISSUES. 331 



sp. gr. 1*1 than the former, remains in solution after the hypoxanthine 

 compound has crystallized out. On supersaturating with ammonia, 

 a gelatinous compound of xanthine and silver (C 5 H 2 Ag 2 N 4 2 + H 2 0) 

 separates. By dissolving in warm nitric acid, the compound 

 C 5 H 4 N 4 O 2 . AgN0 3 is again formed, and from the latter xanthine 

 can be prepared by following a process analogous to that which 

 has been described in the case of hypoxanthine. 



Properties Xanthine when freshly separated from its solutions 



of Xanthine. presents the appearance of white amorphous granules. 



Xanthine is almost completely insoluble in cold water, requiring 

 about 14000 parts of water at 16 G. to dissolve it, and 1400 parts of 

 boiling water. It is easily soluble in solution of ammonia, which 

 deposits it, on evaporation, in the form of indistinctly crystalline 

 plates (Kiihne) : from the ammoniacal solution it is completely pre- 

 cipitated by lead acetate. 



Solutions of other alkalies likewise dissolve xanthine, and from 

 these it is precipitated by acids. 



Reactions Ammoniacal solutions of xanthine when heated with 



>f xanthine. S n ver sa lt s reduce the silver to the metallic state. 



On heating xanthine in hot hydrochloric acid, and evaporating, 

 microscopic crystalline masses, composed of aggregations of hexagonal 

 plates, separate ; these consist of the hydrochlorate of xanthine, 

 C 5 H 4 N 4 O 2 . HC1 + H 2 O. In a similar manner the nitrate is formed 

 (C 5 H 4 N 4 2 . HN0 3 ), and this crystallizes in rhombic plates arranged 

 in clumps. The solution of the nitrate is precipitated by silver 

 nitrate in a flocculent form, and the precipitate may be dissolved 

 in hot nitric acid and allowed to crystallize on cooling ; it has the 

 composition (C S H 4 N 4 2 . AgNO 3 ) ; this body is much more soluble 

 in nitric acid than the corresponding hypoxanthine silver compound. 

 It separates irom its solution in nitric acid in the form of groups of 

 fine needles, which do not resemble the hypoxanthine compound. 



Xanthine (like hypoxanthine) is soluble in pure (colourless) warm 

 nitric acid without the disengagement of gas; on cautious evapo- 

 ration a colourless nitrate is left ; the residue is not rendered purple 

 by ammonia. By these reactions xanthine is distinguished from uric acid. 



Heated with fuming nitric acid containing nitrous acid, a citron- 

 coloured residue is left, which becomes orange or red on the addition 

 of caustic soda, and which when heated exhibits at its margin a 

 fine purple red colour. 



of xanthine According to Scherer 1 the fresh muscles of the 



found in mus- horse contain 0'0026 p. c. of xanthine. 



cle. 



Relations This body, as has been said in treating of hypoxan- 



of xanthine. thine, is closely related to that body and to uric acid. 



1 Scherer, Ann. d. Chem. u. Pharm. Vol. cvn. (1858) p. 314. 



