98 CHEMISTRY OF THE PROTEIDS CHAP. 



2(C 6 H 5 ) 2 CH 2 + 2S = (C H 6 ) 2 C : C(C 6 H 5 ) 2 +^2H 2 S. 



Phenyl-hydrazin reacts similarly (E. Fischer l ). Certain thio-com- 

 pounds are especially apt to split off hydrogen. For example, the 

 following substances become oxidised by the oxygen of the air during 

 evaporation and then give rise to disulphides : Thiophenol (Hiibner 

 and Alsberg 2 ), thio-benzoic acid (Engelhardt 3 ), and benzyl-mercaptane 

 {Marcker 4 ). 



2C 6 H 5 SH + - C 6 H 5 S S . C 6 H 5 + H 2 0. 



Thiophenol Diphenol-disulphide. 



This thiophenol in presence of water and sulphur readily forms H 2 S. 

 If thiophenol be first oxidised with ferricyanide of potash, it does not 

 .split off H 2 S. 



Ethyl-mercaptane also readily splits off H 9 S, and as Morner has 

 shown that egg-white contains a sulphur radical which is not cystin 

 and which is volatile, Heffter assumes egg-white to contain a mercap- 

 tane which brings about the formation of H 2 S, when egg-white and 

 flowers of sulphur are mixed. Serum -albumin and serum -globulin 

 contain only cystin, and they do not form H 2 S. The presence of an 

 unstable hydrogen-atom in albumins explains the reduction of iodates 

 into iodides, ferri-compounds into ferro-compounds, etc., and according 

 to Mann 5 also heat-coagulation. 



(i) Disintegration by means of Enzymes 



Amino-acids are very resisting to boiling with acids and alkalies, 

 and also to the action of pepsin and trypsin (see below), for which 

 reason the amino-group cannot be detached by these means. It can, 

 however, be removed by enzymes, which seem to be common both in 

 plants and in animals. Butkewitsch 6 has studied the action of 

 lower plant -life on albumins and on amino- acids, and Bertel 7 has 

 attempted to show that tyrosin when oxidised gives rise to horno- 

 gentisinic acid, ammonia, and carbon-dioxide. Czapek 8 believes this 

 transformation to be a good proof of the des-amination of amino-acids 

 by means of enzymes, and attributes to the tyrosin -ferment both 



1 E. Fischer, Ber. d. deutsch. chem. Ges. 10. 1334 (1877). 



2 Hiibner and Alsberg, Ann. d. Chem. 156. 330 (1865). 



3 Engelhardt, Latschinoff, and Malyscheff, Zeitschr. f. Chem. 1868, p. 353. 



4 Marcker, Ann. d. Chem. 136. 75 (1865). 



5 Gustav Mann, Physiological Histology, 1902, p. 66. 



6 K. Butkewitsch, Pringsheims Jahrb. f. wissensch. Botanik, 38. 147. 



7 R. Bertel, Ber. d. deutsch. bot. Gesellsh. 2O. 460. 



8 F. Czapek, Hofmeister's Beitrage, 2. 588 (1902). 





