56 HANDBOOK FOR BIO-CHEMICAL LABORATORY. 



in a large flask, provided with a glass stopper, and treated 

 with 2.5 litres chloroform water (2.5 litres tap water with 

 12.5 c.c. chloroform, and shaken until the latter is dissolved); 

 add 2.5 c.c. chloroform, and place this mixture in an incu- 

 bator and allow to digest at 40 C. for two to three days, con- 

 tinually shaking. After digestion transfer to a large dish 

 and heat to boiling, and continue boiling after acidifying with 

 acetic acid until the albumin is precipitated. Now filter, and 

 evaporate the filtrate to 800-1000 c.c. Make alkaline with 

 ammonia, filter off the precipitate formed, and completely 

 precipitate with a 3$ silver-nitrate solution. The gelatinous 

 precipitate formed consists of the silver combination of the 

 xanthin bases. Care must be taken not to have a silver- 

 chloride precipitate form, otherwise more ammonia must be 

 added. Filter off the precipitate, wash well, place the pre- 

 cipitate in a flask while still moist, and dissolve by the aid of 

 heat in nitric acid of sp. gr. 1.1 (equal volumes nitric acid 

 and water), adding a little urea to prevent the formation of 

 nitrous acid. The solution should be nearly clear. Filter 

 while hot and allow to stand for 24 hours. A precipitate of 

 guanin, adenin, and hypoxanthin silver nitrate will have 

 formed, while xanthin silver nitrate remains in solution. 

 Filter and wash with dilute nitric acid. 



Add ammonia to the filtrate until alkaline, when a precipi- 

 tate of xanthin silver nitrate will form as a brownish or red- 

 dish flocculent precipitate. Filter, wash, suspend in water 

 with a few drops ammonia; heat, add a few drops ammonium 

 sulphide, stir, filter off the silver sulphide, and evaporate the 

 filtrate, when xanthin will be obtained. (The silver com- 

 pound may also be decomposed by HC1, but then on evapo- 

 ration xanthin hydrochloride is produced.) The xanthin 

 obtained as above is never quite pure. 



The residue of hypoxanthin, guanin, and adenin silver 

 compounds is suspended in water and decomposed with a 

 current of H a S, filtered, and the filtrate evaporated to a 



