EXAMINATION OF MUSCULAR TISSUE. 27 



(6) By Means of Hydrogen Sulphide. Put the hypoxanthine silver 

 nitrate into a flask with some water and pass in hydrogen sulphide, 

 shaking frequently, until the precipitate appears perfectly black and 

 no white particles are to be seen. Filter: the filtrate contains the 

 hypoxanthine nitrate. Concentrate somewhat on the water-bath in 

 order to drive off the hydrogen sulphide, make faintly alkaline with 

 ammonia, and proceed as above. The disadvantage of this method 

 is that the complete decomposition with hydrogen sulphide is difficult 

 to accomplish and that the hypoxanthine may contain some sulphur. 



The decomposition may be accomplished more readily if the hypo- 

 xanthine silver nitrate is first converted into the silver compound of 

 hypoxanthine by digesting it for some time with water, ammonia, and 

 2 g. of silver nitrate. Filter and * wash the precipitate, suspend it in 

 water, warm, and add ammonium sulphide, drop by drop. The silver 

 sulphide settles on warming; the filtrate on evaporation yields hypo- 

 xanthine (Schindler *). 



For the reactions the hypoxanthine obtained in any one of the 

 above ways is sufficiently pure. In case it is markedly yellow it may 

 be purified in the following manner: Dissolve the hypoxanthine in 

 water by adding hydrochloric acid, add a few drops of ferrous sulphate, 

 heat the solution and make it alkaline with sodium hydroxide, filter, 

 concentrate somewhat, and precipitate the hypoxanthine by acidify- 

 ing faintly with acetic acid or by neutralizing exactly with hydro- 

 chloric acid. Iron, in the form of ferrous hydroxide, often passes into 

 the filtrate on filtering the alkaline solution. It is then necessary to 

 let the filtrate stand for some time, shaking it frequently until the 

 iron has completely separated as ferric hydroxide. 



METHOD B. 



In the method A, owing to the action of the nitric acid on 

 the xanthine bases, so-called nitro compounds may easily be 

 formed and contaminate the hypoxanthine. This may be 

 avoided by getting rid of the substances, which interfere 

 with precipitation of the xanthine bases, not by oxidation 

 with nitric acid, but by precipitation. Dissolve 50 g. of meat 

 extract in 500 cc. of water, add basic lead acetate to the 



1 Zeitschr. f. physiol. Chem., 13, 433. 



