188 THE PROTEIN SUBSTANCES. 



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 difficultly 

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

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

 compound, CsHsNs.CeH^NC^sOH, which is very insoluble and which 

 separates more readily than the hypoxanthine picrate, and which 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 

 which consists in part of leaf-shaped aggregations and in part of cubical 

 or prismatic crystals, often with rounded corners. This compound is 

 used in the microscopic detection of adenine. With the nitric-acid test 

 and with WEIDEL'S reaction adenine acts in the same way as hypoxan- 

 thine. The same is true for its behavior with hydrochloric acid and 

 zinc with subsequent addition of alkali. 



The procedure for the preparation and detection of the four above- 

 described purine bases is, according to KOSSEL and his pupils, as follows: 

 The finely divided organ or tissue is boiled for three or four hours with 

 sulphuric acid of about 5 p. m. The filtered liquid is freed from protein 

 by basic lead acetate, and the new filtrate is treated with sulphuretted 

 hydrogen to remove the lead, again filtered, concentrated, and, after 

 adding an excess of ammonia, precipitated with ammoniacal silver nitrate. 

 The silver compound (with the addition of some urea to prevent nitri- 

 fication) is dissolved in not too large a quantity of boiling nitric acid of 

 sp. gr. 1.1, and this solution filtered boiling hot. On cooling, the silver 

 xanthine remains in the solution, while the double compounds of gua- 

 nine, hypoxanthine, and adenine crystallize out. The silver xan thine 

 may be precipitated from the filtrate by the addition of ammonia and 

 the xanthine set free by means of sulphuretted hydrogen. The three 

 above-mentioned silver-nitrate compounds are decomposed by sulphur- 

 etted hydrogen and the guanine separated from the adenine and hypo- 

 xanthine by treatment while hot with ammonia, in which the guanine in 

 difficultly soluble. 



When the above filtrate containing the adenine and hypoxanthine, 

 which has been, if necessary, freed from ammonia by evaporation, is 

 allowed to cool, the adenine separates, while the hypoxanthine remains 

 in solution. According to BALKE 1 we can advantageously precipitate 

 the purine bases with copper sulphate and hydroxylamine, following 

 the method suggested by KRUGER and ScniTTENHELM 2 for the quanti- 



1 See foot-note 3, page 184. 2 Zeitschr. f. physiol. Chem., 45. 



