23 



mineral acid is removed by evaporation, and the nitrogen present 

 as ammonia determined by distilling with an excess of magnesium 

 oxide ; after separating the magnesia precipitate from the remain- 

 ing solution by filtration, the nitrogen was determined in the pre- 

 cipitate by the Kjcldahl method, the di-amino nitrogen in the fil- 

 trate was precipitated by phosphotungstic acid and determined by 

 the method of Kjeldahl and the mon-amino nitrogen determined 

 by difference. 



He obtained in the acid solution 84.5 per cent of the total nitro- 

 gen in the soil, 52.3 per cent of which was found in the magnesia 

 precipitate. This result is in striking contrast to those obtained by 

 Osborne and Harris (1903) working on pure proteins, where they 

 found that the nitrogen contained in the magnesia precipitate does 

 not usually exceed 4 per cent of the total nitrogen and in most 

 cases is very much less. The amount of nitrogen insoluble in the 

 12 per cent acids used in the digestion may be designated as "hu- 

 min." The nitrogen in the magnesia precipitate has been desig- 

 nated by most investigators "humin" nitrogen. The total "humin" 

 nitrogen in the soil is then represented by the nitrogen in the 

 magnesia precipitate plus that retained by the soil. On -recalcula- 

 tion of his data it was found that the insoluble humin in the soil 

 after hydrolysis amounted to 15.3 per cent of the total nitrogen, 

 making a total humin nitrogen content of 59.1 per cent. This very 

 high result of total humin nitrogen was undoubtedly due to the soil 

 being hydrolyzed only seven hours with a relatively low concen- 

 tration of hydrochloric acid and the insoluble residue boiled the 

 same length of time with sulfuric acid. Complete decomposi- 

 tion of the proteins probably did not take place in the dilute acids 

 used in the short time that they were heated. As a result partially 

 hydrolyzed residues may have been precipitated by the magnesium 

 oxide, which would account for the high results. 



Shorey (1906) concluded that even though we might know 

 much concerning the constitution of the compounds comprising 

 the various groups isolated from protein by this method of analysis, 

 we know nothing concerning their composition when isolated from 

 soil, inasmuch as we are not dealing with a pure protein (cf. also 

 Oiortner 1913, 1914, 1916 c). 



The work of Suzuki (1906-08 c) gives us further knowledge of 

 the individual amino compounds formed in the decomposition of soil 

 organic matter. He worked with three samples of humic acid, o>ne 

 obtained from Merck (origin unknown to Suzuki), one prepared 

 from an unmanured soil, and one from a compost heap. After 

 boiling each preparation for ten hours with strong hydrochloric 

 acid, the undecomposed residue was filtered off, washed, and the 

 residue extracted twice in this manner with strong hydrochloric 

 acid. He determined the amounts dissolved as amide, di-amino, and 

 mon-amino acid nitrogen. From 65 to 75 per cent of the total 

 nitrogen was dissolved by the hydrochloric acid and in the extract 

 41 to 62 per cent of the nitrogen was not precipitated by phospho- 

 tungstic acid. A sample of humic acid was twice extracted, with 



