178 HETEROXANTHIK PARAXANTHIN. 



The older and frequently repeated statements that xanthin and hypoxanthin can 

 be obtained from uric acid by the action of sodium-amalgam, as also that 

 hypoxanthin can be converted into xanthin by treatment with nitric acid have 

 recently been shown to be erroneous. Notwithstanding the similarity of their 

 composition these three substances are incapable of intercon version 1 . 



2. Heteroxanthin. C 6 H 6 N 4 O 2 (Methyl-xanthin ?). 



This substance occurs in minute quantities in the normal urine of 

 man 2 and the dog 3 , along with xanthin and hypoxanthin and another 

 closely allied xanthin-base, paraxanthin. It occurs in larger amount 

 in the urine of leukhaemic patients. It is crystalline, but not very 

 characteristically so, is soluble with difficulty in cold water, much more 

 soluble in hot water, is insoluble in alcohol and in ether. It may, 

 as also may paraxanthin, be separated from other xanthin-bases by 

 taking advantage of the relatively slight solubility of its sodium salt 

 in caustic soda. It also yields with hydrochloric acid a relatively 

 insoluble salt which crystallises readily, whereas the corresponding 

 salt of paraxanthin is readily soluble. They may by this means be 

 separated the one from the other. 



Heteroxanthin does not give the ordinary reaction for xanthin with 

 nitric acid and caustic soda, but yields a brilliant colouration on the 

 application of Weidel's test (see sub xanthin). Like the other 

 xanthin-bases it gives an insoluble salt with an ammoniacal solution of 

 nitrate of silver. 



3. Paraxanthin. C 7 H 8 N 4 2 (Dimethylxanthin ?) Isomeride of 

 Theobromin. 



Like heteroxanthin it occurs in very small amounts in urine 4 . It is 

 soluble with difficulty in cold water, but is more soluble than xanthin ; 

 is much more soluble in hot water, insoluble in alcohol and in ether. It 

 crystallises readily in characteristic flat, somewhat irregular, six-sided 

 tables when its solutions are slowly evaporated, or in needles if 

 rapidly. It forms, as do the preceding substances, a crystalline salt 

 with nitrate of silver ; this like the corresponding compound of xanthin 

 is soluble in strong nitric acid (sp. gr. 1-1) at 100, and may thus be 

 separated from hypoxanthin. It may be separated from xanthin by 

 means of its greater solubility in cold water, and from heteroxanthin 

 by the difference in the solubility of its salts with sodium and 

 hydrochloric acid. 



1 Kossel, Zt.f. physiol. Chem. Bd. vi. (1882), S. 428. Fischer, Ber. d. d. chem. 

 Gesell. 1884, S. 328. 



2 Salomon, Ibid. 1885, S. 3407. 



3 Salomon, Zt.f. physiol. Chem. Bd. xi. (1887), S. 412. 



4 Thudichum, Annals of cli. Med. Vol. i. (1879), p. 166. Salomon, Ber. d. d. 

 chem. Gesell, 1883, S. 195, 1885, 3406, Zt.f. klin. Med.~Bd. vn. (Suppl.-Hft.) (1884), 

 S. 63. Cf. Zt.f. physiol. Chem. Bd. xv. (1891), S. 319. 



