33 

 C. The Method. 



The method of Van Slyke (1911) has been used throughout 

 this investigation because the nitrogen can be separated into a 

 larger number of fractions than when the earlier method of Haus- 

 mann (1899) is employed. The different fractions, however, are 

 not listed in the same manner as in the Van Slyke method, for 

 since we are not dealing- with pure protein material we cannot 

 correctly speak of arginine, histidine, cystine, and lysine nitrogen. 



Van Slyke (1915) has called attention to the fact that his 

 method was devised for the analysis of pure protein material and 

 not for a heterogeneous mixture of nitrogen compounds. This 

 fact was not recognized by certain investigators. Grindley and 

 Slater (1915) applied this method to the analysis ot feeding stuffs 

 in exactly the same manner as though they were dealing with a 

 pure protein. Potter and Snydcr (1915 a) analyzed certain soils 

 and soil extracts and report their fractions as "arginine," "histi- 

 dirtfe," etc. Although they state (p. 2221) : 



It is not thought that nitrogen as found by the Van Slyke method, work- 

 ing with such a complex as the soil, is in reality, all lysine, histidine, etc., 

 nitrogen. It might be said that each group, as found, represents 'a class of 

 compounds having the particular reaction by which the lysine. histidine, etc., 

 nitrogen respectively are determined. 



It is obvious that there are other types of organic materials 

 which will interfere with the nitrogen distribution. It seems very 

 probable that in soils as well as in the material analyzed by Grind- 

 ley and Slater (1915) there must be many organic nitrogen com- 

 pounds which have no relation to the protein molecule, such as 

 purme bases, pyrimidine bases, nitrogenous lipins, nitrogenous pig- 

 ments, as well as other non-protein nitrogenous compounds (cf. 

 the list of non-protein nitrogenous compounds actually isolated 

 from the soil as given in the preceding part of this paper). Gortner 

 (1913) states that much valuable comparative data can be obtained 

 by the application of Van Slyke's method to the analysis of heter- 

 ogeneous materials ; but it is self evident that no analogy can be 

 drawn between the analysis of pure protein and the analysis of a 

 protein mixed with an unknown amount of foreign nitrogenous 

 compounds. The results of Potter and Snyder (1915 a) are of 

 little value in advancing our knowledge of soil proteins or for 

 comparison with analyses of pure proteins, but are extremely 

 valuable and interesting for comparison between themselves and 

 with other analyses of soils carried out under similar conditions. 

 It must be remembered that all data on similar material is strictly 

 comparable when the same method of analysis is followed. 



It is possible that many of the non-protein nitrogenous com- 

 pounds may be split up during the hydrolysis of heterogeneous ma- 

 terial. Gortner (1913) has shown that uric acid nitrogen is dis- 

 tributed in all four of the major fractions after hydrolysis. The 

 ammonia nitrogen amounted to 15.27 per cent, humin nitrogen 

 35.98 per cent, basic nitrogen 12.97 per cent, and non-basic nitrogen 

 3S./8 per cent. "The humin nitrogen contained no trace of black 

 color and was probably calcium ureate." Probably all of the purines 

 and pyrimidines would behave in a similar manner. 



