CHEMISTRY OF THE LEUCOMAINES. 311 



bonate, filtered, and the filtrate, after the addition of sodium 

 acetate, is strongly acidulated with hydrochloric acid. This 

 precipitates the guanine, together with some uric acid. The 

 precipitate is dissolved in boiling hydrochloric acid, and the 

 guanine then thrown out of solution by the addition of am- 

 monium hydrate. Guanine is also obtained in the decom- 

 position of nuclein with dilute acids, and can, therefore, be 

 prepared from such cellular organs as the spleen, pan- 

 creas, etc., according to the method given on page 285. It 

 should be noted here that in the decomposition of the mixed 

 silver compounds with hydrogen sulphide or ammonium 

 sulphide (Schindler) the guanine, often only in part, passes 

 into solution with adenine and hypoxanthine, and the re- 

 mainder is held back in the silver sulphide precipitate. The 

 latter should, therefore, be boiled with dilute hydrochloric 

 acid, and on saturating the filtrate with.ammonia the guan- 

 ine after a while separates. That portion of the guanine 

 which did pass into solution with the other two bases is 

 separated from them by digestion with ammonia on a water- 

 bath. The two portions are then combined, transferred to 

 a filter, previously dried at 110° and weighed, washed well 

 with ammonia, then dried and weighed. 



The free base forms a white, amorphous powder, insol- 

 uble in water, alcohol, ether, and ammonium hydrate ; 

 easily soluble in mineral acids, fixed alkalies, and in excess 

 of concentrated ammonium hydrate. It can be heated to 

 above 200° without undergoing decomposition. When 

 evaporated with strong nitric acid it gives a yellow residue, 

 and this on the addition of sodium hydrate assumes a red 

 color, which on heating becomes purple, then indigo-blue ; 

 on cooling it returns to a yellow, passing through purple 

 and reddish-yellow shades due, according to V. Brucke, to 

 absorption of water. This is the so-called xanthine reac- 

 tion, and is supposed to be due to the formation of xanthine 

 and a nitro product. It is given best by guanine, then by 

 xanthine, and is not given by either hypoxanthine or 

 adenine. 



Nitrous acid converts it directly into xanthine, thus : 



C^H^N^O + HNO, = C,H,NA + N, -f- H,0. 



