176 



XAKTHIN. 



Many members of this group are both derivable from and convertible 

 into other members of the group by simple chemical processes, but this 

 relationship of the one to the other will be more fully appreciated by 

 consideration of the properties and reactions of the separate substances. 

 Their relationships to uric acid and each other are in many cases 

 indicated by comparison of their formulae. 



Xanthin. C 5 H 4 N 4 2 . 



NH CH 



CO C NH, 

 NH C = N 



;CO (Fischer) 1 . 



First discovered in a urinary calculus, and called xanthic oxide. 

 More recently it has been found as a normal, though very scanty, 

 constituent of urine, muscles, and several other tissues, such as the liver, 

 spleen, thymus, brain-substance, &c. It occurs in larger quantities, 

 together with hypoxanthin, in ' extract of meat,' and is also found in 

 traces in vegetable tissues, lupins, malt seedlings and tea. In nearly 

 all cases it is accompanied by hypoxanthin. The amount which is 

 present in any of the above tissues and fluids is so small that none of 

 them, except perhaps the extract of meat, affords a convenient source 

 for its preparation 2 . To obtain it in quantity guanin is treated with 

 nitrous acid 3 , and the nitro-product thus obtained is reduced in am- 

 moniacal solution with ferrous sulphate. It may also be prepared 

 artificially from hydrocyanic acid and water in presence of acetic acid 4 . 

 When pure it is a colourless powder, requiring about 14000 parts of 

 water for its solution at ordinary temperatures and 1400 at 100. 

 Insoluble in alcohol and in ether, it dissolves readily in dilute acids 



FIG. 23. XANTHIN HYDROCHLORIDE, 

 C 5 H 4 N 4 2 . HC1. (Kiihne.) 



FIG. 24. XANTHIN NITRATE, 

 C 5 H 4 N 4 2 . HN0 3 . (Ktihne.) 



and alkalis (characteristically in ammonia) forming crystallisable 

 compounds. 



1 (i) Ber. d. d. chem. Gesell. 1882, S. 453. (ii) Ann. d. Chem. u. Pharm. Bd. 

 ccxv. (1882), S. 253. 



2 For its separation from urine see Neubauer, Zt. f. anal. Chem. Bd. vn. (1868), 

 S. 398. From muscle-extract see Stadeler, Ann. d. Chem. u. Pharm. Bd. cxvi. 

 (1860), S. 102. Neubauer, Zt. f. anal. Chem. Bde. n. (1863), S. 26, vi. (1867), S. 33. 



3 Fischer, loc. cit. (ii). 



4 Gautier, Compt. Rend. T. 98 (1884), 1523. 



