44 CHEMISTRY OF THE PROTEIDS CHAP. 



test, and in many cases the reaction shows a different colour from 

 the pure red of the peptone reaction. This feeble and impure biuret 

 reaction was found frequently to resist strongly the dissociating action 

 of ferments. The idea suggests itself that in these cases we are deal- 

 ing with histidin derived from the peptones. 



A full description of the salts of histidin is given by Kossel and 

 Kutscher ; x the picrolonic salt, which because of its slight solubility 

 might be used for purposes of isolation, has been prepared by Steudel. 2 

 The free base is laevo-rotatory : 



a D = -3-974. 



The salts are, however, dextro-rotatory. Bauer 3 has investigated the 

 shape of the crystals. See, further, Pauly, 4 who also gives directions 

 for the preparation of histidin. 



The inter-relation of imido-azol compounds to grape sugar is referred 

 to by the author in the chapter dealing with the carbohydrate radical 

 of albumin. 



15. Diamino-trioxy-dodecanoic Acid, C 12 H 26 N 2 5 , is a satu- 

 rated, aliphatic, oxy-amino-acid, reacting acid to litmus, with a feebly 

 bitter taste and readily soluble in dilute acids. It has been prepared 

 by Fischer and Abderhalden from the impure tyrosin-fraction obtained 

 by the hydrolysis of casein with boiling sulphuric acid. It resembles 

 Skraup's caseinic acid 5 as far as the ratio of C : N : is concerned, but 

 contains considerably more H. 



The following acids (except No. 19) have been discovered by 

 Skraup : 6 



16. Diamino-glutaric Acid, C 5 H 10 N 2 4 



<X NH 2 H NH 2 ^0 



-)C C C C Cf 

 HCT H H H X OH. 



17. Diamino-adipic Acid, C 6 H 12 N 2 4 



(k NH 2 H H NH 2 ,Q 



Jc c c c c of 



HO 7 H H H H X OH. 



Adipic acid is COOH (CH 2 ) 4 COOH. 



18. Diamino-dihydroxy-suberic Acid, C 8 H 16 N 2 6 . 



1 A. Kossel and F. Kutscher, Zeitschr. f.physiol. Chem. 28. 382 (1899). 



2 H. Steudel, ibid. 37. 219 (1902). 3 M. Bauer, ibid. 22. 285 (1896), 



4 Herm. Pauly, ibid. 42. 508 (1904). 



5 Zd. H. Skraup, Ber. d. deutsch. chem. Ges. 37. 1596 (1904). 



6 Zd. H. Skraup, Sitzb. Akad. d. Wiss. Wien, 113. II. b p. 263 (1904), and in 

 Zeitschr. f. physiol. Chem. 42. 276 (1904). 



