THE XANTHIN-BASES. 383 



xanthin on platinum foil with nitric acid a yellow spot remains, 

 which turns red when moistened with a drop of sodium hydrate 

 solution. On further heating, it becames a beautiful purplish violet. 

 The reaction is thus similar to the murexid test for uric acid, but it 

 will be noted that in this case a red color develops on the addition 

 of the alkali, while with uric acid a blue color is obtained. 



HOPPE-SEYLER'S TEST. A few crystals of xanthin are placed 

 in a watch-crystal containing a mixture of a few drops of a solution 

 of sodium hydrate and of calcium hypochlorite. A dark-green zone 

 then appears about the xanthin, which subsequently turns brown 

 and ultimately disappears. 



WEIDEL'S TEST. A small amount of xanthin is covered with 

 freshly prepared chlorine- water containing a trace of nitric acid. The 

 mixture is evaporated to dryness on a water-bath, and the residue 

 exposed to the fumes of ammonia, when a beautiful red or purplish- 

 violet color develops. 



Hypoxanthin (Sarcin). Hypoxanthin crystallizes in small white 

 needles. It is soluble in hot water, less readily so in cold water, 

 while in cold alcohol it is almost insoluble. Like xanthin, it dis- 

 solves with comparative ease in dilute solutions of the alkaline 

 hydrates and acids, forming salts, which are decomposed by distilled 

 water, with the liberation of the free base. Of these, the chlorhydrate 

 is fairly characteristic, as on rapid evaporation it crystallizes out in 

 distinct whetstone crystals similar to those of uric acid. On treat- 

 ing the substance in ammoniacal solution with an ammoniacal 

 solution of silver nitrate, a double salt of hypoxanthin with silver 

 is precipitated, which is soluble with difficulty in boiling nitric acid. 

 On cooling, it separates out in the form of curiously bent prisms, 

 which are quite characteristic. On boiling with a solution of acetate 

 of copper, hypoxanthin is thrown down as a ctipric salt. 



Test. The substance does not give the common reactions of 

 xanthin. When treated with zinc and hydrochloric acid, however, 

 hypoxanthin gives rise to a ruby-red color, which later changes to a 

 brownish red, when sodium hydrate solution is added in excess. 



Guanin. Guanin is usually obtained in amorphous form, but can 

 be brought to crystallize out from its solutions in strong ammonia, 

 on spontaneous evaporation. It is insoluble in water, alcohol, and 

 ether. In mineral acids it dissolves with comparative ease, at the 

 same time forming salt-like products, which are crystallizable, but 

 quite unstable, so that in the case of some of them at least the free 

 base is liberated by water. With the common alkalies it likewise 

 combines to form compounds which are somewhat soluble in warm 

 water, but more readily so if a little fixed alkali is present. In 

 ammonia it dissolves with great difficulty, so that it is possible to 

 precipitate the substance from its acid solutions by the addition of 

 ammonia. Silver nitrate precipitates the substance from its solu- 

 tions in nitric acid as a double salt, which dissolves in boiling nitric 

 acid, and crystallizes out on cooling in the form of fine needles. On 



