324 BACTERIAL POISONS. 



ated slowly, and the precipitate which forms is finally washed 

 with alcohol and ether. 



The original amraoniacal mother-liquors of heteroxan- 

 thine yield on further concentration amorphous floccules of 

 xanthine, which are remoyed by filtration ; from the filtrate, 

 when concentrated still more, paraxanthine crystallizes out. 



Paraxanthine is obtained in colorless, glassy, generally 

 six-sided plates, which are arranged in tufts or rosettes; 

 From very concentrated aqueous solutions it crystallizes in 

 long, colorless, interwoven needles, which on drying exhibit 

 the silky lustre of tyrosin. The crystals belong to the 

 monoclinic system, and may crystallize with as well as 

 without water. If water is present on careful heating (110) 

 the crystals lose their brilliancy and become whitish and 

 opaque, and at 120-130 the water is completely driven 

 off. The conditions under which crystals containing water 

 are formed are not known ; probably by slow crystalliza- 

 tion, whereas rapid crystallization from hot concentrated 

 solution yields the anhydrous needles. At about 170-180 

 sublimation takes place. The melting-point is at atxnit 

 284 (KosSEL). It can be heated to 250 without melting 

 or sutfering any decomposition, but when heated more 

 strongly it gives oft' white vapors which possess a distinct 

 iso-nitril odor, at the same time it carbonizes and takes fire. 

 When evaporated with concentrated nitric acid, as in the 

 ordinary xanthine test, it gives only a slight yellow residue. 

 On the other hand, WEIDEL'S test, evaporation with chlo- 

 rine water containing a trace of nitric acid, and then placing 

 the dry residue into an ammoniacal atmosphere under a 

 bell-jar, gives a beautiful rose-red color. 



It is difficultly soluble in cold water (though more easily 

 than xanthine); somewhat more readily soluble in hot 

 water, and insoluble in ether and alcohol. It is soluble in 

 ammonium hydrate, hydrochloric acid, and nitric acid. Its 

 solutions are neutral in reaction. 



Silver nitrate produces in nitric acid, as well as in ammo- 

 niacal solutions, a flocculent or gelatinous precipitate, which 

 in concentrated solutions forms an almost perfect jelly-like 

 mass. This silver precipitate is soluble in \\ann nitric 



