44 RESEARCHES ON THE NITROGENOUS NON-ALBUMINOUS 
was allowed to cool, when a beautiful white crystalline precipi¬ 
tate was formed, which was immediately separated by filtration. 
For further purification, the crystals were once more dissolved 
in the said reagent and allowed to recrystallize. The purified 
substance formed, when viewed under the microscope, long 
colourless needles not blackened by exposure to light and bearing 
the closest resemblance to hypoxanthine silver nitrate prepared 
form the pure substance. The purified silver compound 
was digested in ammonia in which a little silver nitrate was 
dissolved, then filtered, washed with cold water, suspended in 
hot water, and decomposed by hydrogen sulphide. The filtrate 
from silver sulphide was evaporated to dryness, when a faintly 
coloured crystalline powder was left behind. This substance, 
when evaporated with nitric acid, left a slightly yellowish 
residue, which dissolved in caustic potash without any coloura¬ 
tion. It produced a faint rose-red colour when treated with 
chlorine water and ammonia gas. 1 According to A. Kossel, 2 
Weidel’s colour-reaction does not properly belong to hypoxan¬ 
thine but to xanthine, these two substances being most generally 
found in company. The same author 3 also found that adenin 
gives the same colour reaction as xanthine. Hence the substance 
in view might have contained, in spite of repeated recrystalliza¬ 
tion, a minute quantity of xanthine or adenin, but it is quite 
certain that it was hypoxanthine. 
The nitric acid solution from which hypoxanthine and guan- 
nine-silver compounds were separated threw down, after a few 
days, a pretty large quantity of a white crystalline precipitate. 
An addition of ammonia in slight excess to this solution 
produced a large qnantity of a flocculent slightly yellowish 
precipitate. The precipitate was separated by filtration, washed 
with cold water, suspended in hot water, and finally decom¬ 
posed by hydrogen sulphide. The filtrate from silver sulphide, 
1 Fresenius, Zeitschrift für analytische Chemie, 1872, p. 96. 
2 Zeitschrift für physiologische Chemie, Vol, 6, p. 426. 
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