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IV. SUMMARY. 



This paper deals with a study of the nitrogen distribution in 

 different soil types, by applying Van Slyke's method. Tables have 

 been presented showing such distribution for the following mate- 

 rials : 



a. Fibrin hydrolyzed in the presence of an ignited mineral 



subsoil (together with data of fibrin hydrolyzed alone 

 and in the presence of carbohydrates). 



b. A calcareous black grass-peat. 



c. An acid, sphagnum-covered peat, hydrolyzed alone, in the 



presence of a mineral subsoil, and in the presence of 

 stannous chloride. 



d. An acid "muck" soil 



e. Seven samples of mineral surface soil representing the fol- 



lowing soil types : Fargo clay loam, Fargo silt loam, 

 Carrington silt loam (two samples from different glacial 

 drifts), Hempstead silt loam, prairie-covered loess, and 

 forest-covered loess. 



f . Extracts of a sphagnum-covered peat and of a calcareous 

 black grass-peat soluble in (a) 1 per cent hydrochloric 

 acid, (b) 4 per cent sodium hydroxide but precipitated 

 by acid, and (c) 4 per cent sodium hydroxide and not 

 precipitated by hydrochloric acid. 



The following conclusions are evident : 



1. The figures for the ammonia nitrogen in a protein analysis 

 are not appreciably changed when the hydrolysis is carried out in 

 the presence of an ignited mineral soil equal to twenty times the 

 weight of the protein material. 



2. The "humin" nitrogen is greatly increased by the addition 

 of ignited mineral soil. It was shown that histidine nitrogen cannot 

 account for this increase, neither is it due to the presence of car- 

 bohydrates, since the soil lost all its organic matter on ignition. 



3. Attention has been called to the fact that the analysis of 

 a pure protein in the presence of even an ignited mineral soil docs 

 not give reliable results for the different fractions, and that such 

 determinations are of value only when used for purposes of com- 

 parison. Such data should not be compared with analyses ot pure 

 proteins. 



4. Since practically all mineral soils give furfural on treat- 

 ment with acid it is very likely that a very considerable amount 

 of the total humin nitrogen found is due to the presence of carbohy- 

 drates in the soil, which give rise to furfural during hydrolysis. 

 This may combine with certain of the nitrogenous compounds and 

 cause an increase in the "humin" nitrogen, as well as adsorb or 

 occlude nitrogenous compounds in the "humin" formed from fur- 

 fural by polymerization. 



