SEPARATION OF THE PUBIN BASES. 411 



The filtrate from the xanthin nitrate saturated with ammonia and 

 concentrated yields a satin-like mass consisting of microscopic plates 

 of \-methyl xanthin. The remainder in solution can be precipitated 

 with ammoniacal silver solution or with copper sulphate. 



2. The filtrate from the xanthin fraction on addition of a slight 

 excess of ammonia yields at once a precipitate of glistening prisms 

 — epiguanin. This is filtered ofi" and the ammonia is expelled from 

 the filtrate by heating. The solution which should not be too con- 

 centrated is then treated in the cold with a 1.1 per cent, solution of 

 picric acid to a slight excess. The adenin picrate is at once removed 

 by means of a suction pump. 



The filtrate from the adenin is acidulated with sulphuric acid and 

 extracted with benzol or toluol to remove picric acid. After which 

 the remaining bases are precipitated with ammoniacal silver solution 

 or with copper sulphate and bisulphite. The precipitate is decom- 

 posed with hydrogen sulphid after which the aqueous filtrate is 

 evaporated to dryness. Portions of 3 g. each, of the dry residue, 

 are dissolved in 100 c.c. of hot dilute nitric acid (90 c.c. HjO 

 -|- 10 c.c. cone. HNO3). On cooling pure hypoxanthin nitrate sep- 

 arates out. 



The filtrate from this deposit contains small amounts of hypoxan- 

 thin, heteroxanthin, and 1-methyl xanthin besides paraxanthin. To 

 separate these bases the entire method is repeated from the begin- 

 ning. The above filtrate is precipitated with ammoniacal silver so- 

 lution or with copper sulphate and sodium bisulphite. The hydro- 

 chloric acid filtrate, obtained by decomposing the precipitate in the 

 manner previously described, is evaporated and the residue is ex- 

 tracted as before with as little cold water as possible. The insoluble 

 portion contains heteroxanthin and 1-methyl xanthin, and these are 

 separated by means of a 3.3 per cent, solution of sodium hydrate. 

 The filtrate contains hypoxanthin and paraxanthin. In order to re- 

 move the hydrochloric acid these bases are again precipitated as 

 silver or copper compounds. These are decomposed and the dry 

 residue dissolved in a little hot dilute nitric acid (as above) yields on 

 cooling hypoxanthin nitrate. The filtrate contains paraxanthin 

 which can be obtained now as the sodium salt or as the free base. 



Guanin, if present, is to be expected in both fractions. The xan- 

 thin fraction, treated with ammonia, would yield the insoluble guanin. 

 From the hypoxanthin fraction guanin and epiguanin would be pre- 

 cipitated together by ammonia. It can be separated from the latter 

 by treatment with hot water or hot dilute ammonia. 



Inasmuch as caffein and theobromin are not precipitated by am- 

 moniacal silver solution or by the copper sulphate method it is neces- 

 sary in order to detect these bases to resort to precipitation with 

 phosphotungstic acid. For this purpose the urine, acidulated with 

 sulphuric acid, is treated with this reagent. The precipitate is de- 



