388 CHEMISTRY OF THE LEUCOMAINS. 



the mother-liquor change, like the sulphate, to a different form 

 (Fischer). Gold chlorid yields a precipitate of fine yellow needles 

 which, if dissolved in warm water and the solution allowed to 

 evaporate slowly in the cold, form macroscopic, glistening, polyhedric 

 crystals. 



Potassium bichromate when added to a solution of the chlorid 

 yields in a short time fine, glistening, four-sided yellow prisms. 



With silver nitrate and ammonia the aqueous solution of the base 

 gives a gelatinous precipitate. Silver nitrate added to the nitric 

 acid solution of the base gives a colorless amorphous precipitate 

 which when recrystallized from hot dilute acid forms fine needles 

 (Fischer). Copper sulphate and sodium bisulphite in the cold like- 

 wise produce a gelatinous precipitate, which in warm solutions how- 

 ever is flocculent. Copper sulphate and sodium thiosulphate pro- 

 duce in warm solutions a flocculent white precipitate which later 

 turns to brown. 



While mercuric chlorid produces in solutions of adenin and of 

 hypoxanthin (0.1 to 500) an immediate flocculent precipitate, with 

 epiguanin a considerable excess of the reagent is necessary and then 

 only a cloudiness results. 



An aqueous solution of the base is not thrown down by lead 

 acetate, neutral or basic ; nor by lead acetate and ammonia in which 

 respect it behaves like adenin whereas hypoxanthin is completely 

 precipitated by this reagent as a heavy, flocculent or gelatinous pre- 

 cipitate. As Kriiger and Salomon point out an ammoniacal solution 

 of lead acetate may by itself on standing give a deposit which should 

 not be mistaken for a precipitate of the base. 



On evaporation with concentrated nitric acid it leaves a yellow 

 residue which with sodium hydrate becomes orange-red ; on heating 

 this becomes darker and even slightly violet (xanthin reaction). 

 Evaporated with hydrochloric acid and a chlorate it gives a white 

 residue which with ammonia vapors become violet red (murexid test). 



With nitrous acid it readily yields heteroxanthin (7-methyl xan- 

 thin), and on cleavage with chlorin it gives guanidin (Fischer ^). 



Xanthin, C^H^N^Oj, was discovered by Marcet in 1817 in a 

 urinary calculus and since then it has been frequently found as the 

 only or chief constituent of many calculi. It was not synthesized 

 until 1897 when Fischer' prepared it in two ways from tri-chlor- 

 purin. In 1900 Traube' prepared it, as well as guanin, uric acid 

 and the methyl xanthins, from urea and cyanacetic acid. 



Although obviously present in the urine it was not isolated there- 

 from until very recently. It is a normal constituent but is present 



^Berlchte, 30, 2413. 

 'Berkhte, 30, 2232 ; 31, 2562. 

 'Berichte, 33, 1371, 3035. 



