88 CHEMISTRY OF THE PROTEIDS CHAP; 



other organic compounds, and in particular from carbohydrates. 

 Hoppe-Seyler states that 25 per cent of cane-sugar may be converted 

 into humin - substances in a few hours. The humin - substances 

 prepared from sugar are, in their dry state, black or brown powders 

 having a peculiar glitter. In water and acids they are insoluble, 

 while in alkalies a certain percentage becomes peculiarly slippery, 

 while the greater percentage Mulder's humic acid is readily soluble. 

 From such alkaline solutions they are precipitated by acids. Hoppe- 

 Seyler gives for humin prepared from cane-sugar this percentage 

 composition : 



= 63-88, H = 4-64, -31'48. 



The high percentage of carbon and the low percentage of hydrogen 

 is characteristic of all humin substances, whatever their source 

 may be. They contain protocatechuic acid, in addition to which 

 Udransky isolated, by fusion with alkalies, formic acid, oxalic acid, 

 and pyrocatechin 1 : 2 C 6 H 4 (OH) 2 . Samuely further found pyridin, 

 C 5 H 5 N, and pyrrol, C 4 H 4 NH. 



If, in addition to carbohydrates, ammonia or other nitrogenous 

 substances are in solution, then the humins combine with the 

 ammonia and become thereby nitrogenous. Analogously they may 

 also take up sulphur and iron. For a preparation which was made 

 by boiling serum albumin with 25 per cent hydrochloric acid, 

 Schmiedeberg calculated the following percentage : 



C = 66-27, H - 5-49, N = 5-57, and a little sulphur. 

 For another preparation, made from Witte's peptone, 

 = 60-34, H = 4-86, N = 8'09, S = 0'96. 



Schmiedeberg lays special stress on the fact that the composition 

 in the two preparations is not the same. Humin substances owe their 

 existence undoubtedly to a secondary reaction. Schmiedeberg has 

 shown that the greater part of an albumin-molecule absorbs water and 

 then gives rise to amino-acids ; but this change is accompanied by an 

 accessory reaction, as is usually the case amongst organic bodies, in 

 consequence of which 1 to 2 per cent of the albumin is transformed into 

 a compound rich in carbon, but poor in hydrogen and nitrogen. Per- 

 haps it is more probable that the dissociation -products, which are 

 formed at first, undergo subsequently a secondary change, as held by 

 Langstein l and Samuely. Amongst the dissociation-products may be 

 mentioned : 



1. Glucosamin and other carbohydrates. 



1 L. Langstein, Zeitschr.f. physiol. Chem. 31. 49 (1900). 



