66 



tached to the sides of the flask in which the hydrolysis was carried 

 out. 



These experiments suggest interesting possibilities, but dis- 

 cussion must be deferred until we know more of the exact reac- 

 tions taking place. 



The true humin nitrogen remains in the residual soil after 

 hydrolysis. The amount of nitrogen in this fraction varies from 

 22.93 per cent to 28.27 per cent of the total nitrogen for the mineral 

 soils studied. This represents more nearly the true humin nitrogen, 

 in that the black coloring matter formed by acid hydrolysis remains 

 in this portion, but in addition we should also find here all organic 

 nitrogenous compounds insoluble in fairly strong solution of hy- 

 drochloric acid, all of the nitrogen adsorbed by the carbohydrate 

 humins, etc. Potter an'd Snyder (1915 a) express surprise at the 

 large proportion of nitrogen in this fraction but when one considers 

 the heterogeneous nature of the soil organic matter it is perhaps 

 more surprising to find that over 60 per cent of the nitrogenous 

 compounds are soluble in strong hydrochloric acid. Further study 

 is necessary before the full significance and origin of this humin 

 nitrogen can be thoroughly understood. 



C. The effect of the quantity of acid used for the hydrolysis 

 on the amount of nitrogen dissolved and the nitrogen distribution 

 in soils. Throughout this investigation acid at least as strong as 

 constant boiling hydrochloric acid was used for the hydrolysis 

 since that is the strength recommended for the analysis of pure 

 proteins. 



In the case of two soils, however, one of the duplicates was 

 hydrolyzed in the presence of 1000 cc. concentrated acid to 250 

 grams of soil, the other being hydrolyzed in the presence of 500 

 cc. of constant boiling acid to 250 grams of soil, in order to see if 

 any noticeable differences would be observed on the resulting analy- 

 ses. The two soils thus hydrolyzed were the prairie-covered loess 

 and forest-covered loess. 



The results show little difference between the duplicates. 

 Table XXV shows that the larger volume of the stronger acid dis- 

 solved a greater per cent of the soil, due to the fact that more of 

 the mineral constituents were soluble in acid of this concentration. 

 At the same time, however, the amount of nitrogen extracted was 

 less. 



D. The percentage of soil nitrogen extracted by acid hydro- 

 lysis. Shorey (1905) working with a single Hawaiian soil ex- 

 tracted 84.68 'per cent of the total soil- nitrogen by acid hydrolysis. 

 Jodidi (1911) working with eleven Iowa soils found from his 

 'studies a minimum of 68.90 per cent, a maximum' of 83.94 per cent, 

 and an average of 75.77 per cent; Lathrop and Brown (1911) in 

 five Pennsylvania soils found a minimum of 70.60 per cent, a maxi- 

 mum of 73.71 per cent, and an average of 71.78 per cent; Shmook 

 (1914), working with four Russian soils, found a minimum of 

 60.60 per cent in the Laterite soil, a maximum of 87.67 per cent in 

 the Podzol soil, and an average of 68.33 per cent; Kelley (1914), 



