410 CHEMISTRY OF THE LEUOOMAINS. 



water-bath by cautious addition of dilute hydrochloric acid till the 

 origiDal voluminous precipitate is replaced by that of silver chlorid. 

 The liquid is then heated over a flame and hydrochloric acid, equal 

 to that already used, is added. The solution is filtered while hot 

 and the precipitate, which contains most of the uric acid, is thoroughly 

 washed with very dilute hydrochloric acid. 



When the copper method is used the precipitate, after thorough 

 washing with boiling water, is transferred to a flask, then warmed 

 and rendered alkaline with ammonium hydrate. The liquid is then 

 strongly acidulated with hydrochloric acid and the copper is pre- 

 cipitated by means of hydrogen sulphid. The precipitate is filtered 

 while hot and freely washed. It contains the greater part of the 

 uric acid. 



The acid filtrate obtained by either method is concentrated on 

 the water-bath, preferably at a low temperature and with constant 

 stirring. To remove the acid from the syrupy residue this is twice 

 taken up with water and reevaporated. This operation is repeated 

 with 96 per cent, alcohol till the acid is expelled and the residue be- 

 comes granular. This is then digested for several hours at 40° with 

 distilled water ; the insoluble part is filtered ofl' and washed with water, 

 then with alcohol and with ether. The aqueous filtrate, evaporated 

 and the residue treated as before, may yield a slight insoluble por- 

 tion which is to be combined with the main quantity. 



The insoluble residue contains xanthin, heteroxanthin, and 

 1 -methyl xanthin. The aqueous filtrate contains adenin, hypoxan- 

 thin, paraxanthin and epiguanin with traces of heteroxanljiin and 

 1-methyl xanthin. In other words xanthin and hypoxanthin frac- 

 tions result the same as in Neubauer's method with the difference 

 that paraxanthin appears in the latter. 



1. In order to separate the three bases present in the xanthin 

 fraction the insoluble residue is dissolved in fifteen parts of hot 3.3 

 per cent, sodium hydrate (HCl free). Within 24 hours the sodium 

 salt of heteroxanthin separates out pure and almost quantitatively. 



This is filtered off and the filtrate is divided into portions of 60 

 c.c. and warmed to 60°. Each portion is then poured slowly and 

 with constant stirring into a cold mixture of 20 c.c. of concentrated 

 nitric acid and 20 c.c. of water. This dilute acid should be boiled 

 before being used. The uric acid remaining in solution is thus de- 

 stroyed and the solution on standing a few hours in the cold yields 

 a precipitate of xanthin nitrate. This, if pure, is a heavy crystal- 

 line powder consisting of masses of plates. If impure, the air- 

 dried precipitate should be divided into portions of 3 g., each of 

 which is then dissolved in warm sodium hydrate and the solution 

 diluted to 60 c.c. is treated as before. To obtain free xanthin the 

 nitrate is dissolved in ammonia and from the solution when evapo- 

 rated xanthin separates out in amprphous crusts. 



