382 THE MUSCLE-TISSUE. 



thrown down as double silver salts. They are filtered off and dis- 

 solved in a small amount of hot nitric acid. The solution is placed 

 in the refrigerator when the salts of hypoxanthin and guanin crystal- 

 lize out. The filtrate is termed B. 



To separate the guanin from the hypoxanthin, the material is sus- 

 pended in water; the liquid is brought to the boiling-point and 

 treated with a solution of ammonium sulphide 1 , drop by drop. The 

 silver salts are thus decomposed. The liquid is filtered while 

 hot. The filtrate C contains a portion of the guanin and all of 

 the hypoxanthin, while a fraction of the guanin remains in the 

 precipitate. This can be extracted by boiling with a very dilute 

 solution of hydrochloric acid, when the free base is precipitated 

 by adding an excess of ammonia to the acid solution. Filtrate C 

 is placed on a water-bath and treated with ammonia, when the 

 remaining portion of the guanin is thrown down. The hypoxanthin 

 is then obtained after filtration on evaporating the ammoniacal 

 solution. 



Filtrate B contains the xanthin salt of silver nitrate. To isolate 

 the free base the double salt is first precipitated from its acid solu- 

 tion by ammonia. It is suspended in water, decomposed with 

 hydrogen sulphide, and extracted with ammonia. On evaporation 

 the xanthin crystallizes out. 



This method is well adapted for extracting the xanthin bases 

 from any organs of the body, and also serves for the isolation of 

 adenin. Should this be present, it is found in filtrate C. On adding 

 ammonia the adenin together with the hypoxanthin remains in solu- 

 tion. On cooling the adenin separates out, especially after the 

 ammonia has been evaporated oif. Hypoxanthin remains in solu- 

 tion and is obtained on final evaporation. 



As the general chemical relations of the xanthin-bases have 

 already been considered (page 101), it will suffice to give a brief 

 account of the more important properties of the individual sub- 

 stances at this place. 



Xanthin. Pure xanthin is either amorphous or occurs in the form 

 of fine platelets which are gathered into little clumps so that the 

 material often presents a granular aspect. In cold water it is almost 

 insoluble, and in hot water also it dissolves with difficulty. In 

 alcohol and ether it is insoluble. In acids and alkalies it dissolves 

 with comparative ease, but at the same time it combines with these 

 to form compounds, which are for the most part readily crystalliz- 

 able. From its ammoniacal solution it is obtained as such on evapo- 

 ration of the ammonia. From this solution it is thrown down 

 by silver nitrate as a gelatinous precipitate of the composition 

 C 5 H 4 N 4 O 2 .Ag 2 O. If this is dissolved in nitric acid, a double salt 

 results, which crystallizes out on standing. Unlike hypoxanthin, 

 xanthin is precipitated by an ammoniacal solution of lead sub- 

 acetate. From its aqueous solution it is precipitated as a greenish- 

 yellow material by means of cupric acetate on boiling. 



Tests. NITRIC ACID TEST. On evaporating a few crystals of 



