XANTHIN. 393 



more so than the corresponding salt of hypoxanthin, and is deposited 

 in glistening six-sided plates, often forming aggregations. Its solu- 

 tion does not precipitate platinum chlorid. The nitrate forms fine 

 yellow crystals which when pure are colorless. 



The sulphate, CjH^Np^-HjSO^ -|- Hfi, crystallizes in microscopic, 

 glistening, rhombic plates, decomposable by water. 



With baryta water xanthin forms the difiScultly soluble compound 

 C5H^N^02.Ba(OH)2 , which corresponds to the hypoxanthin salt 

 C5H,Np.Ba(0H)j, and to that of guanin. 



On the addition of a very small amount of sodium hydrate to 

 xanthin it dissolves, and very soon small white needles separate. 

 The crystals dissolve in excess of alkali. This xanthin-sodium 

 compound, C^HgNaN^O^ -|- H^O, is also obtained by passing carbonic 

 acid into an alkaline solution of xanthin. It forms small bunched 

 needles, which are rather easily soluble in water, imparting an 

 alkaline reaction. On the addition of acetic acid the pure white base 

 is thrown down. The compound is partly dissociated by hot water, 

 and resembles the corresponding primary uric acid salts. It is 

 probable that xanthin can form, like uric acid, a soluble secondary 

 salt, since with excess of sodium hydrate it forms a readily soluble 

 compound which probably contains two atoms of sodium. For the 

 reactions of this compound, see page 373. (See heteroxanthin and 

 paraxanthin.) It does not give a mono-methyl xanthin by heating 

 with methyl iodid (Balke). The water of crystallization is expelled 

 only at 190°- 200°. 



From ammoniacal solution silver nitrate precipitates the colorless 

 compound CjH^N^Oj.AgjO, which is unaltered by short boiling and 

 is insoluble in ammonia, but soluble in hot nitric acid. From the 

 nitric acid solution, on long standing, there separates the compound 

 CjH^N^Oj.AgNOj, which, on contact with water, decomposes, giving 

 off nitric acid. The ammoniacal solution is also precipitated by 

 lead acetate — separation from hypoxanthin — also by calcium and 

 zinc chlorids. Cupric acetate gives a precipitate only on boiling. 

 The aqueous solution is not precipitated by lead acetate, but is by 

 phosphomolybdic and phosphotungstic acids, by mercurous and mer- 

 curic salts. Picric acid gives an easily soluble compound, which re- 

 sembles that of hypoxanthin, but differs from that of guanin. Xan- 

 thin gives with a copper solution and a reducing substance (Drechsel's 

 reaction, see page 353) a milk-white precipitate which eventually 

 becomes bluish-green (Balke). Since xanthin has more imido groups 

 than adenin or hypoxanthin and less than uric acid, it is probable 

 that the solubility of the copper compound will be between the 

 solubilities of the corresponding compounds of hypoxanthin and 

 uric acid ; that is, between 1 : 250,000 and 1 : 360,000, the solubili- 

 ties respectively in hot water. The copper compound of uric acid is 

 soluble in 560,000 parts of cold water (Kriiger). 



