HETEBOtANTEIN. 399 



solutions a precipitate which readily dissolves on warming in even 

 very dilute nitric acid ; from this solution, if not too concentrated, 

 the heteroxanthin silver nitrate compound crystallizes in character- 

 istic well formed plate-like prismatic crystals which are often 

 crossed. They are soluble in about 2,800 parts of nitric acid of 1.1 

 specific gravity (Kriiger and Salomon). Copper acetate produces in 

 the cold, in solutions of heteroxanthin, a clear green precipitate. The 

 base is also precipitated by phosphotungstic acid, and by ammoniacal 

 basic lead acetate. Picric acid does not give a yellow-colored pre- 

 cipitate in solutions of the hydrochlorid. 



Mercuric chlorid readily precipitates heteroxanthin in the form of 

 a grayish-yellow compound, which on standing twelve or twenty-four 

 hours becomes converted into pure white crystalline aggregations. 

 This mercuric compound can be converted directly into the corre- 

 sponding silver compound by the addition of silver nitrate and am- 

 monia, as described under paraxanthin. For Drechsel's reaction 

 with copper, see page 353. The precipitate that forms is gelatinous, 

 milk-white, but soon turns green, as in the case of guanin and xan- 

 thin. The solubility of the copper compound would be about the 

 same as adenin and hypoxanthin, since it has two imido groups. 

 The addition of barium chlorid to an ammoniacal solution of the 

 base gives a gelatinous precipitate which is rather soluble in hot 

 water and recrystallizes on cooling in rosettes or balls, (CjHjN^OJ^Ba. 



This base resembles paraxanthin in its property of yielding a diffi- 

 cultly soluble precipitate with fixed alkali. This reaction is best 

 brought about by dissolving the heteroxanthin hydrochlorid in warm 

 dilute sodium hydrate, when, on cooling, the corresponding sodium 

 salt will crystallize out in oblique-angled plates ; or clear long prisms, 

 (CjHjN^OjNa -f- SHjO), Kriiger and Salomon.' Long-pointed twin 

 crystals are the most characteristic. The crystals show greater vari- 

 ations in form than those of paraxanthin. The behavior of the 

 twin crystals with polarized light is of service in identification. 

 These crystals dissolve easily in water, and on neutralization of the 

 solution with an acid a dense pulverulent precipitate of heteroxanthin 

 forms. This sodium compound, as well as that of paraxanthin, is 

 permanent, non-deliquescent ; on moderate heating becomes cloudy, 

 and melts above 300°. It is more difficultly soluble in water than 

 the paraxanthin compound ; the solution has an alkaline reaction. It 

 is soluble in mineral acids and ammonia ; the latter redeposits it 

 unchanged on evaporation. On neutralization of its solution with 

 mineral acids or with lactic, acetic or carbonic acids, the pure base 

 separates out as amorphous or crystalloidal roundish or rosette-like 

 masses, while paraxanthin under the same conditions forms its charac- 

 teristic crystals. The sodium is also removed from both compounds 

 by borax, potassium bisulphate, biphosphate of sodium, bisulphite of 

 1 ZeiU. physiol. Chem., 24, 370. 



