65 



gether with the calcium salts of nitrogenous organic acids, the 

 calcium salts of the purine and pyrimidine bases in addition to 

 the humin formed from the protein material, and other organic 

 compounds that are adsorbed, absorbed, occluded, or combined with 

 the iron and aluminum hydroxides present. 



From Table XXVI we find that from 4.84 to 9.21 per cent of 

 the total nitrogen is precipitated by calcium hydroxide. It can 

 readily be seen that this does not represent true humin nitrogen, 

 since the calcium hydroxide does not contain any black colored sub- 

 stances formed by hydrolysis. The solution from which it is pre- 

 cipitated is colored only by ferric compounds, therefore, the or- 

 ganic material in this precipitate must consist of colorless organic 

 compounds adsorbed by or combined with the lime. This por- . 

 tion of the nitrogen consists almost certainly of non-protein mate- 

 rial. In all pure proteins the nitrogen retained in the calcium hy- 

 droxide precipitate is supposed to consist entirely of deeply colored 

 compounds. This study of the. distribution of organic nitrogen 

 in the soil has led to a new fraction, not previously reported. Cer- 

 tain of the analyses were carried out before the importance 

 of this fraction was realized, but in most of the analyses I have 

 reported this fraction as "nitrogen precipitated by calcium hy- 

 droxide," because of its unknown nature. Further investigations of 

 this fraction are highly desirable. 



Another point of interest is observed in the humin nitrogen of 

 the sphagnum-covered peat hydrolyzed in the presence of metallic 

 tin. There is a decided decrease in this fraction as compared with 

 the peat hydrolyzed alone. As noted earlier, Samuely (1902), sug- 

 gested that humin formation might be due to an oxidation process 

 and certain of the earlier workers (cf. Hlasiwetz and Habermann 

 1871 and 1873) hydrolyzed protein in the presence of stannous chlo- 

 ride in order to obtain a colorless solution instead of one deeply 

 colored by the presence of humin. 



I, therefore, hydrolyzed some gliadin in the presence of tin and 

 found that while the solution remained colorless, nevertheless small 

 balls of black material were formed. The humin nitrogen (insolu- 

 ble in acid + that pptd. by Ca(OH) 2 ) was 1.17 per cent of the total 

 nitrogen, while gliadin hydrolyzed alone gave a dark colored hy- 

 drolysate and a humin nitrogen content of only 0.67 per cent. 



Recently Spriestersbach (private communication) has hydro- 

 lyzed fibrin (from a different sample than mine) alone and in the 

 presence of stannous chloride and finds in the fibrin hydrolyzed 

 alone 1.67 per cent of total humin nitrogen, of which 1.06 per cent 

 is "acid insoluble" (cf. Gortner 1916 c) and 0.61 per cent precipi- 

 tated by calcium hydroxide. In the sample of fibrin hydrolyzed 

 in the presence of tin he finds 0.91 per cent of total humin nitrogen, 

 of which 0.25 per cent is "acid insoluble" and 0.66 per cent pre- 

 cipitated by calcium hydroxide. The nature of his hydrolysate 

 agreed in all respects with mine, i.e., was colorless or faint straw 

 color, with tiny black balls of humin floating on the surface or at- 



