HUMIN-SUBSTANCES 87 



Casein (Merck) /< . - . 0'82 

 Glycocoll .;. v; . 11-10 

 Aspartic acid . .^ . 7*70 



Pyrrolidine-carboxylic acid 0'37 

 Arginin carbonate . . 0'12 

 Lysin hydrochloride . . O'lO 



Leucin . . 0'68 I Glucosamin hydrochloride O'OS 



Negative results were obtained with alanin, glutaminic acid, tyrosin, 

 and tryptophane. 



The formation of prussic acid from glycocoll probably takes place 

 over nitroso- acetic acid which, according to Cramer, 1 breaks down 

 when heated to 1 20 into prussic acid, carbonic acid, and water, thus : 



NH 2 . CH 2 COOH + 20 - NOH . CH COOH + H 2 

 NOH . CH COOH + heat - HCN + C0 2 + H 2 O. 



Plimmer believes the formation of oxaminic acid as observed by 

 Kutscher and Schenk, when they oxidised gelatine with calcium per- 

 manganate, to be also explainable on the supposition that nitroso-acetic 

 acid is the first oxidation-product of glycocoll, if, as v. Peckmann 2 

 suggests, the nitroso-acetic acid undergoes the Beckmann rearrange- 

 ment into the isomeric acid amide, namely, oxaminic acid. 



NOH . CH COOH becomes NH 2 . CO . COOH. 



The formation of prussic acid from aspartic acid is as yet unex- 

 plainable. 



Humin Substances or Melanoidins 



The term ' humin ' was introduced in 1838 by Berzelius, 3 as a sub- 

 stitute for the expressions ' ulmin ' and ' geine,' which he had used pre- 

 viously in describing certain deeply-coloured constituents of * humus ' 

 or mould. 



Mulder then showed that albumins on being boiled with strong 

 hydrochloric or sulphuric acids separate off flocculi of a brown or 

 black colour, which resemble the deeply -coloured bodies seen in 

 putrefying matter. 



These substances have been investigated later, especially by 

 v. Udranszky, 4 Hoppe-Seyler, 5 Schmiedeberg, 6 and Samuely. 7 Humin- 

 substances are not only formed from albumins, but also from many 



1 C. Cramer, JSer. d. deutsch. chem. Ges. 25. 715 (1892). 



2 H. v. Peckmann and K. Wehsarg, ibid. 21. 2991 (1888). 



3 Berzelius, Poggendorff's Ann. 44. 375 (1838). 



. 4 L. v. Udranszky, Zeitschr. f. physiol. Chem. 11. 537, where the older literature 

 is given ; 12. 33 (1887). 



5 F. Hoppe-Seyler, ibid. 13. 66 (1889). 



6 0. Schmiedeberg, Arch. f. experiment. Path. u. Pharm. 39. 1 (1897). 



7 F. Samuely, Hofmeister's Beitrage, 2. 355 (1902). 



