CHEMISTRY OF THE LEDCOMAINES. 323 



little urea, then decomposed with hydrogen sulphide, and 

 the filtrate, rendered alkaline with ammonium iiydrate, is 

 concentrated to a small volume. On stauding, pure hypo- 

 xanthiue crystallizes out. The filtrate from the silver salt 

 of hypoxanthine on being rendered alkaline with ammonium 

 hydrate gives a precipitate which formerly was regarded as 

 consisting entirely of the Xanthine silver compound, but 

 which from the investigations of Salomon, has been showQ 

 to be a mixture of the salts of xanthine, paraxanthine, 

 and heteroxanthine. 



The separation of these bases is effected by the solubility 

 of the free bases in ammonium hydrate. For this purpose 

 the precipitate of the mixed silver salts is decomposed with 

 hydrogen sulphide, and the filtrate, rendered ammoniacal to 

 remove traces of phosphates and oxalates, is moderately 

 concentrated. After standing twenty-four hours, heteroxan- 

 thine crystallizes out, partly in finely formed sheaves and 

 tufts of needles, partly in radially striated masses. The 

 fluid is decanted from the crust of heteroxanthine which 

 forms in the bottom of the beaker, and after being concen- 

 trated somewhat is again allowed to stand. In this way a 

 second crop is obtained, and this is repeated till finally the 

 separated masses scarcely give a precipitate with sodium 

 hydrate. All the heteroxanthine is now united and dis- 

 solved in a little hot water by the aid of sodium hydrate. 

 After twenty-four hours the greater part of the heteroxan- 

 thine crystallizes out in bunches of crystals of sodiiim 

 heteroxanthine, while a small part together with any traces 

 of xanthine remains in solution. The crystalline mass is 

 dried by pressure, dissolved in a little water, and the solu- 

 tion neutralized by addition of hydrochloric acid, when the 

 heteroxanthine separates as a pulverulent precipitate. To 

 remove any traces of paraxanthine, dissolve in hydrochloric 

 acid ; on standing forty-eight hours the heteroxanthine salt 

 separates, while the easily soluble salt of paraxanthine 

 remains in solution. To obtain the pure free heteroxan- 

 thine, the hydrochloric salt is evaporated with ammonium 

 hydrate ; the well-washed residue of heteroxanthine is then 

 dissolved in dilute ammonia, the solution filtered, evapor- 



