EXAMINATION OF MUSCULAR TISSUE. 29 



and the insolubility of its compound with silver nitrate in 

 nitric acid, and also by the crystal form of this compound. 



Detection of Xanthine. 



The filtrate from hypoxanthine silver nitrate contains 

 xanthine, as previously stated, but only in small quantity. 

 Make it alkaline with ammonia (or, in order to save ammonia, 

 neutralize the greater part of the acid with soda or lime and 

 then make alkaline with ammonia). Xanthine silver pre- 

 cipitates in brown or reddish flakes. These are filtered off, 

 washed, suspended in water, some drops of ammonia added, 

 heated, treated with a few drops of ammonium sulphide, 

 shaken thoroughly, filtered from the silver sulphide, and 

 evaporated (or the precipitate may also be decomposed with 

 hydrochloric acid and xanthine hydrochloride obtained on 

 evaporation). Very frequently the silver sulphide passes 

 through the filter; we then evaporate to dryness and extract 

 the residue with boiling water. The xanthine thus obtained 

 is usually not quite pure and the quantity is very small. It 

 suffices, however, for the xanthine test as well as for the so- 

 called Weidel's reaction. 



Xanthine, C 5 H 4 N 4 2 , occurring very rarely in the form of' 

 stone in the bladder, results, like the hypoxanthine, from the 

 decomposition of the nucleins (A. Kossel). In cold water 

 it is practically insoluble (14,151 parts at 16). In alcohol 

 and ether it is insoluble. In hot water it is very difficultly 

 soluble, but it is soluble in caustic soda and ammonia as well 

 as in acids, forming salts. 



1. Xanthine Test. Dissolve the residue or half of it in 

 nitric acid and evaporate cautiously to dryness on a crucible 

 cover over a small flame. A lemon-yellow residue results, 

 which becomes intensely red on moistening with caustic soda, 

 and on further heating purplish red. Add a few drops of 

 water and warm ; a yellow solution results, which again gives 



