86 



CHEMISTKY OF THE PEOTEIDS 



CHAP. 



give rise to compounds analogous to glycocoll-anhyc^ride ; the forma- 

 tion of such compounds is readily explained, for Abderhalden boils 

 amino-acids for several hours with mineral acids and then esterifies 

 them. This explanation does not hold good in the case of Salaskin, 

 but peptic digestion is apt to give rise to bodies after the type of 

 leucyl-leucin (see below, p. 127), and from the latter leucinimide may 

 readily be formed. 1 Therefore the leucinimide, found after dissociating 

 albumins with acids, represents leucin which has been changed, and 

 must be calculated as leucin and be added to the latter. Its melting- 

 point is 271. 



Compounds analogous to leucinimide are formed probably also 

 from the other mono-amino-acids, for the same reasons as leucinimide 

 is formed from leucin, and they seem to have only escaped observation 

 because of the small amounts in which they are formed. 



11. Prussic Acid, HCN. When employing Neumann's method 2 

 for converting albumins into ash, Aders Plimmer 3 noticed the presence 

 of silver cyanide in the precipitate of silver chloride. He found that 

 freshly precipitated silver cyanide is quantitatively converted into 

 prussic acid, HCN, on being boiled with dilute nitric acid. After 

 having destroyed the amino- groups of the albumin -molecule with 

 nitrous acid, the same amount of HCN was obtained as previously, 

 and he therefore concluded 'that the prussic acid originates from a 

 decomposition : product which does not contain nitrogen in the form of 

 amino-groups.' The same amount of prussic acid is obtained as with 

 Neumann's method, if oxidation is brought about with potassium 

 bichromate and sulphuric acid in suitable proportions, while * oxida- 

 tion with manganese dioxide and sulphuric acid, potassium perman- 

 ganate and sulphuric acid, and concentrated sulphuric acid does not 

 give rise to prussic acid, or in very small amount only.' In a second 

 paper 4 Aders Plimmer describes how the amount of prussic acid 

 obtained by oxidation with chromic acid is in general greater than by 

 oxidation with Neumann's nitric and sulphuric acid mixture. 



The mean-percentages of HCN after oxidising with chromic acid 

 are as follows : 



Gelatine . . . . 2 '75 

 Casein (hydrolysed) . . 1'25 

 Haemoglobin (Merck) . T13 



Fibrin (Merck) 

 Witte's peptone 

 Egg-albumin . 



1-11 

 0-94 



0-88 



1 E. Fischer and E. Fourneau, Ber. d. deutsch. chem. Ges. 34. II. 2868 (1901). 



2 A. Neumann, Zeitschr. f.physiol. Chem. 37. 115 (1902), and 43. 32 (1904). 



3 R. H. Aders Plimmer, Journ. of Physiol. 31. 65 (1904)t Here too is given the 

 older literature. 



4 R. H. Aders Plimmer, ibid. 32. 51 (1904).' i 



