34 LABORATORY WORK IX PHYSIOLOGICAL CHEMISTRY. 



After removal of the alcohol, the filtrate is made ammo- 

 niacal with NH 4 OH and ammoniacal AgN0 3 solution added 

 until no further precipitation occurs. This precipitate is 

 composed of the double silver salts of all the purine bases. 

 These silver combinations, after their removal from the 

 solution by filtration, are dissolved in boiling-hot HX0 3 

 (sp. gr. 1.1) and the mixture filtered hot. 



In this reaction the silver nitrate compounds of the bases 

 are formed, all of which are soluble in the hot nitric acid solu- 

 tion. Upon cooling, the guanine, adenine, and hypoxan- 

 thine combinations crystallize out, but the xanthine remains 

 in the solution, from which, after filtration and treatment 

 with NH 4 OH in excess, it is thrown down as a reddish 

 precipitate (xanthine silver oxide). This precipitate, sus- 

 pended in its solution, is next treated with hydrogen sulphide 

 and the mixture warmed and filtered. The xanthine will 

 crystallize out of the filtrate upon concentration. 



The precipitate of the three other bases is suspended in 

 water and treated with hydrogen sulphide, warmed and 

 filtered hot in the same manner as the xanthine. After con- 

 centration the solution is saturated with NB^OH and digested 

 on the water-bath. The guanine remains insoluble, while 

 the other two bases pass into solution. Filter the mixture 

 hot. From this filtrate when freed from the ammonia and 

 allowed to cool, the adenine separates, leaving the hypoxan- 

 thine in the solution. 



(a) Try some of the crystals with murexide test. 



(6) Examine the various precipitates for crystals. Make 

 sketches of them. 



(c) Warm some of the xanthine crystals with bromine- 

 water and evaporate the solution to dryness on the water- 

 bath. Allow ammonia vapors to come in contact with the 

 residue; this becomes red. 



