392 OSEMISTRr OF THE LEUCOMAINS. 



it is yellowish, and even when prepared from guanin it is still col- 

 ored. The decoloration can be effected, according to Balke, by con- 

 verting the xanthin into the mono-sodium compound which can be 

 recrystallized and then decomposed with acetic acid. The base is 

 thus obtained in snow-white floccules. 



It is difficultly soluble in cold water (about 14,000 parts), alco- 

 hol, and ether ; somewhat more soluble in boiling water (about 1,200 

 parts). It is soluble in alkalis and alkali carbonates, not bicarbon- 

 ates, and from these solutions it is precipitated on neutralization 

 with acids, or by passing carbonic acid. In warm ammonia it dis- 

 solves more readily than does uric acid or guanin, and on cooling the 

 ammonium compound recrystallizes. The solubility in cold, even 

 strongly acid solutions, is very slight (Wulff). It acts as a weak 

 base and as a weak acid ; with salts of the heavy metals it forms 

 difficultly soluble or insoluble compounds. Its basic properties, 

 however, are weaker than those of hypoxanthin or guanin„ 



When xanthin is evaporated with nitric acid it leaves a lemon- 

 yellow residue (hence its name), which is not changed by ammonium 

 hydrate — distinction from uric acid — but with potassium hydrate be- 

 comes yellowish-red, on heating purple-red. This, the so-called xan- 

 thin reaction, is not given by hypoxanthin or by adenin. On the 

 other hand, when evaporated with chlorin water, or with hydro- 

 chloric acid and a chlorate, it yields a residue which with ammonia 

 gives the murexid test (Fischer,^ Kossel). 



When added to a mixture of bleaching powder and sodium hydrate 

 in a watch-glass the solution becomes covered by a dark-green scum, 

 which changes to a brown, and soon disappears — distinction from 

 hypoxanthin. 



On heating xanthin a small portion volatilizes ; the greater part 

 decomposes into ammonium carbonate, cyanogen, and hydrocyanic 

 acid. Heated at 200° with hydrochloric acid, it decomposes with 

 the formation of ammonia, carbonic acid, formic acid, and glycocoU 

 (E. Schmidt, see p. 342). When bromin is allowed to act on 

 xanthin, there is formed a substitution compound, having the for- 

 mula CjHjBrNPjj- It may also be obtained by the action of nitrous 

 acid on bromguanin (p. 383). Brom-xanthin is easily prepared and 

 can be readily changed to brom-caffein which in turn can be con- 

 verted into ethoxy- and hydroxy-caffein or into caffein itself. 

 Obviously this is a crucial test for the recognition of xanthin 

 (Fischer)." The synthetic chlor-xanthin is easily converted in like 

 manner. With potassium chlorate and hydrochloric acid it yields 

 alloxan and urea (p. 341). 



Xanthin is a weak base, which dissolves in acids with the forma- 

 tion of salts. 



The hydrochlorid, C^H^NPjj.HCl, is difficultly soluble in water, 



'BericMe, 30, 2236. 

 ^Berichte, 31, 2563. 



