402 CHEMISTRY OF THE LEUCOMAINS. 



hydrate, hydrochloric acid, and nitric acid. Its solutions are neu- 

 tral in reaction. 



Silver nitrate produces in nitric acid, as well as in ammoniacal 

 solutions, a floceulent or gelatinous precipitate, which in concen- 

 trated solutions forms an almost perfect jelly-like mass. This silver 

 precipitate is soluble in warm nitric acid, from which on cooling it 

 separates in white crystalline tufts possessing a silky luster. On 

 decomposition with hydrogen sulphid the silver salt yields pure 

 paraxanthin. Picric acid produces in the hydrochloric acid solution 

 a precipitate consisting of densely felted yellow crystalline spangles. 

 It is also precipitated by phosphotungstic acid and copper acetate ; 

 mercuric chlorid when added in excess gives after some time a pre- 

 cipitate composed of a mass of colorless prisms, which are rather 

 difficultly soluble in water j easily in hot water. The crystals of 

 paraxanthin mercuric chlorid when moderately heated become 

 opaque from loss of water of crystallization ; at a higher temperature 

 they melt, undergoing at the same time partial decomposition, and 

 on strong heating they evolve disagreeable nauseating vapors. The 

 aqueous solution of this mercuric double salt gives with silver nitrate 

 an abundant precipitate of silver chlorid, which disappears on the 

 addition of ammonium hydrate, and is replaced by the floceulent 

 gelatinous precipitate of silver paraxanthin. The hydrochloric acid 

 solution of paraxanthin crystallizes with difficulty even when strongly 

 concentrated, and on the addition of platinum chlorid it yields a 

 well crystallizable orange-colored paraxanthin platinochlorid. It is 

 not precipitated by basic lead acetate nor by mercuric nitrate. 

 Copper solutions, in the presence of reducing substances, give a 

 floceulent milk-white precipitate, which on washing turns greenish 

 by oxidation (Balke, p. 353). Picric acid gives a yellow precipi- 

 tate in a hydrochloric acid solution of the base. 



Like heteroxanthin it yields a characteristic difficultly soluble 

 sodium salt which can be made use of for purpose of identification 

 and separation. The sodium salt has the formula C^HjN^OjNa 

 -\- 4H2O. It forms, upon the addition of sodium hydrate to a con- 

 centrated solution of the base, a precipitate of long, glittering, crys- 

 talline spangles which under the microscope are seen to consist of 

 delicate rectangular, often longitudinally striated plates which are 

 isolated or united in tufts. The plates show double refraction. Be- 

 sides these crystals there are also present hexagonal plates resembling 

 cystin. The crystals are soluble in a little water, or on warming, 

 but precipitate again on cooling. Paraxanthin, although it shares 

 with heteroxanthin the property of forming a difficultly soluble 

 compound with fixed alkalis, however can be distinguished from the 

 latter by neutralizing with an acid the solution of the sodium or 

 potassium compound, when, in the case of paraxanthin, there will 

 be obtained a precipitate of the characteristic crystals of that base ; 



