XANTHINE. 189 



advantage in their precipitation (KRUGER) 1 . This behavior of the 

 purine bases serves just as well as the behavior with the silver solution 

 for their precipitation and preparation. 



HN CO 



I I 

 Xanthine, C 5 H4N 4 2 , = OC C NH v (2, 6-dioxypurine) , is found 



I II >CH 



HN-C W 



in several cellular organs. It occurs in small quantities as a physio- 

 logical constituent of urine, and it occasionally has been found as a urinary 

 sediment, or calculus. It was first observed in such a stone by MARCET. 

 Xanthine is found in larger amounts in a few varieties of guano (Jarvis 

 guano) . 



Xanthine can be prepared, according to E. FISCHER, by boiling uric 

 acid with 25 per cent hydrochloric acid or, according to SuNDViK, 2 by 

 heating uric acid with anhydrous oxalic acid in glycerin to about 200 C. 



Xanthine is amorphous, or forms granular masses of crystals, or may 

 also, according to HoRBACZEWSKi, 3 separate as masses of shining, thin, 

 large rhombic plates with 1 mol. water of crystallization. It is very 

 slightly soluble in water, in 14,151-14,600 parts at 16 C., and in 1300- 

 1500 parts at 100 C. (ALMEN 4 ). It is insoluble in alcohol or ether, but 

 is readily dissolved by alkalies and with difficulty by dilute acids. With 

 hydrochloric acid it gives a crystalline, difficultly soluble combination. 

 With very little caustic soda it gives a readily crystallizable compound, 

 which is easily dissolved by an excess of alkali. Xanthine dissolved in 

 ammonia gives with silver nitrate an insoluble, gelatinous precipitate 

 of silver xanthine. This precipitate is dissolved by hot nitric acid, and 

 by this means an easily soluble crystalline double compound is formed. 

 Xanthine in aqueous solution is precipitated on boiling with copper 

 acetate. At ordinary temperatures xanthine is precipitated by mercuric 

 chloride and by ammoniacal basic lead acetate. It is not precipitated 

 by basic lead acetate alone. 



When evaporated to dryness in a porcelain dish with nitric acid, 

 xanthine gives a yellow residue, which turns, on the addition of caustic 

 soda, first red, and after heating, purple-red. If we place some chlorinated 

 lime with some caustic soda in a porcelain dish and add the xanthine 



1 Balke, Zur Kenntnis der Xanthinkorper, Inaug.-Diss. Leipzig, 1893 ; Kriiger 

 Zeitschr. f. physiol. Chem., 18. 



2 E. Fischer, Ber. d. d. chem. Gesellsch, 43; Sundvik, Zeitschr. f. physiol.Chem. 

 76. In regard to the synthesis of xanthine and other purines see E. Fischer, footnote 

 3, p. 186. 



s Zeitschr. f. physiol. Chem., 23. 



4 Journ. f. prakt. Chem., 96. 



