192 THE PROTEIN SUBSTANCES. 



formed, which when dried at 120 C. has a constant composition, 

 2(C5H2Ag2N40)H20, and is used in the quantitative estimation of 

 hypoxanthine. Hypoxanthine picrate is soluble with difficulty, but 

 if a boiling-hot solution of it is treated with a neutral or only faintly 

 acid solution of silver nitrate the hypoxanthine is almost quantitatively 

 precipitated as the compound CsHsAgN^.Ce^CNC^sOH. Hypo- 

 xanthine does not yield an insoluble compound with metaphosphoric 

 acid. When treated, like xanthine, with nitric acid, it yields, an almost 

 colorless residue which, on warming with alkali, does not turn red. Hypo- 

 xanthine does not give WEIDEL'S reaction. After the action of hydro- 

 chloric acid and zinc upon a hypoxanthine solution, followed by the 

 addition of an excess of alkali a ruby-red color develops, followed by 

 a brownish-red color (KOSSEL). According to E. FISCHER 1 a red 

 coloration occurs even in the acid solution. 

 N C.NH 2 



Adenine, C5H5N5, = HC C NH\ (6-aminopurine), was first found 

 II II >CH 



N C N ' 



by KOSSEL 2 in the pancreas. It occurs in all nucleated cells, but in 

 greatest quantities in the sperm of the carp and in the thymus. Adenine 

 has also been found in lucsemic urine (STADTHAGEN 3 ) . It may be obtained 

 in large quantities from tea-leaves. 



Adenine crystallizes with 3 molecules of water of crystallisation in 

 long needles which gradually become opaque in the air, but much more 

 rapidly when warmed. If the crystals are warmed slowly with a quan- 

 tity of water insufficient for solution, they suddenly become cloudy at 

 53 C., a characteristic reaction for adenine. It dissolves in 1086 parts 

 cold water, but is easily soluble in warm. It is insoluble in ether, but 

 somewhat soluble in hot alcohol and easily so in acids and alkalies. It 

 is more easily soluble in ammonia solution than guanine, but less soluble 

 than hypoxanthine. The silver compound of adenine is soluble with 

 difficulty in warm nitric acid, and deposits on cooling as a crystalline 

 mixture of adenine silver nitrates. With picric acid adenine forms a 

 compound, CsHsNs.Ce^CNC^sOH, which is very insoluble but 

 separates more readily than the hypoxanthine picrate, and can be 

 used in the quantitative estimation of adenine. We also have an adenine 

 mercury-picrate. Metaphosphoric acid with adenine gives a precipitate 

 which dissolves in an excess of the acid if the solution is not too dilute. 

 Adenine hydrochloride gives with gold chloride a double compound 



1 Kossel, Zeitschr. f. physiol. Chem., 12, 252; E. Fischer, 1. c. 



2 See Zeitschr. f. physiol. Chem., 10 and 12. 

 1 Virchow's Arch., 109. 



