2i6 Organic Constituents of Soils [Jan. 



The filtrate {2y) is allowed to cool, is made ammoniacal, and 

 ammoniacal silver nitrate sol. added iintil precipitation ceases. If 

 xanthine and hypoxanthine are present, they will be precipitated as 

 xanthine silver and hypoxanthine silver. 



The silver salts are collected on a filter paper and washed with 

 water. The filter and precipitate (28) are placed in an evaporation 

 dish, boiled for a minute with nitric acid sol. (i.i sp. gr.), filtered 

 hot, washed with the same strength of acid sol. and allowed to cool. 

 Hypoxanthine silver nitrate crystallizes out after several hours and 

 is filtered off. 



To the filtrate (29), ammonium hydroxide is added in excess, 

 the precipitate is collected on a filter, washed well with water, and, 

 after Suspension in water, is decomposed with hj^drogen sulfide, the 

 excess of the latter being removed by boiling, and xanthine identi- 

 fied by its color reactions and characteristic salts. 



The precipitate (30) is washed until the washings give a neutra' 

 reaction, suspended in water, and decomposed with hydrogen sul- 

 fide; excess of hydrogen sulfide is expelled, slight excess of am- 

 monia is added, the sol. warmed to remove the excess of the latter 

 and, after filtering, conc. to small volume. The sol. is then allowed 

 to stand in a cool place, when the hypoxanthine should crystallize 

 out in small colorless needles. 



The second portion (31 ) (see page 211) consisting of one-fourth 

 of the original alkaline extract of the soll, is made rather strongly 

 acid with sulfuric acid. The humus precipitate (32) so obtained, 

 after thorough washing, may be added to the humus precipitate 

 from (2) and the filtrate may be shaken out with ether as described 

 in (13) and the ether extract added to (14). After such treatment 

 the filtrate (33) is precipitated with a sol. of phosphotungstic acid 

 and allowed to stand for several days. 



The precipitate (34) thus formed is collected on a filter and the 

 filtrate discarded. The precipitate is washed thoroughly with 5 per 

 Cent sulfuric acid sol., decomposed by heating with barium hydrox- 

 ide sol. and the liquid filtered. The filtrate is acidulated with dil. 

 nitric acid and silver nitrate is added until a drop of the sol. added to 

 a saturated sol. of barium hydroxide causes a yellow color to persist. 

 Barium hydroxide is then added to slight alkalinity to precipitate 

 histidine and the sol. is filtered. 



