25 



di-amino acids precipitated by phosphotungstic acid. The nitrogen 

 in the precipitate of di-amino acids was determined by the method 

 of Kjeldahl. The filtrate from the di-amino acids containing the 

 mon-amino acids was oxidized by the Kjeldahl method and the 

 nitrogen determined. In some cases he secured the mon-amino 

 nitrogen by difference, stating that it was difficult to get a direct 

 determination of the mon-amino nitrogen by the Kjeldahl method. 

 He states that 



this percentage was usually higher than the one directly found by kjeldahl- 

 izing the filtrate from the phosphotung-istic acid precipitate. 



In one experiment the percentage of mon-amino nitrogen by 

 direct determination was 62.83 per cent, while by difference the 

 result was 67.22, and in another case the results were 64.25 and 

 65.06 respectively. 



It will be noted that this is a departure from the method used 

 by Shorey (1905) in that here the nitrogen is separated into three 

 fractions instead of the usual four. v The nitrogen in the magnesia 

 precipitate was distributed with the di-amino and mon-amino acid 

 nitrogen. This method of nitrogen distribution will be classed 

 as "Jodidi numbers" (in contrast to the Hausmann numbers) in 

 the subsequent portion of the paper. 



Van Slyke's (1910) nitrous acid method was first applied by 

 Robinson (1911) to a study of peat soil, in order to determine the 

 amount of amino^nitrogen present. The ammonia nitrogen was re- 

 moved by previous distillation with magnesium oxide. The only 

 value of Robinson's work seems to be in the fact that his figures 

 for total and amino nitrogen increase to a maximum with in- 

 creasing time of hydrolysis, in much the same manner that pro- 

 teins react ; thus indicating that the amino groups were not ex- 

 isting free in the peat but in some form of combination which 

 did not react with nitrous acid. For example, after one hour's 

 hydrolysis the total nitrogen of the soil in solution amounted to 

 29.86 per cent, while the amino nitrogen was 4.62 per cent or a 

 ratio exceeding 6:1. After forty-two hours' hydrolysis the nitro- 

 gen of the soil in solution was 51.54 per cent of the total nitrogen 

 and the amino nitrogen was 25.07 or a ratio only slightly exceed- 

 ing 2:1. This ratio increases again with further hydrolysis so 

 that at the end of 138 hours the ratio is almost 3:1. However, the 

 amount of nitrogen in solution was so small that the experimental 

 error of measuring total and amino nitrogen must have been 

 quite large. 



More recently Jodidi (1911) made a study of some Iowa soils 

 using a modification of the Osborne and Harris (1903) method. 

 The nitrogen removed from the solution by the magnesium oxide 

 was ignored by the author.* This contained a part of the so-called 

 "htimin" nitrogen. Subtracting the sum of the ammonia** and 

 di-amino nitrogen from 100 he found the per cent of the nitrogen in 



^Experimental data presented later in this paper will show that this 

 fraction may exceed 9 per cent of the total nitrogen. 



**He distinguishes the ammonia nitrogen originally present in the soil 

 as such, from that produced by acid hydrolysis. 



