420 Biochemical Studies of Heated Soils [Mar. 



To determine the soluble matter the 50 c.c. samples of each ex- 

 tract were evaporated to dryness in platinum dishes, dried at 108 

 to constant weight and this weight recorded as total solids. The 

 residues were carefully ashed at a low red heat, dried and weighed 

 again, and this weight recorded as inorganic matter. The difference 

 between this weight and the weight of the total solids was recorded 

 as organic matter. Total nitrogen was determined in another 50 

 c.c. portion by the official method for nitrogen, including that in the 

 form of nitrates, etc. 14 The analytical results were very interest- 

 ing. We give two typical series of such data in Tables 1 and 2. 



From such figures one may conclude, as was done in our previous 

 paper and in the papers of others, that dry heat causes the production 

 in soils of large amounts of soluble material. The more striking 

 fact is that the increase of soluble matter goes hand in hand with the 

 temperature to which the soil was subjected. It occurred to us 

 that the objection might be raised that in our experiments it was the 

 duration of the heating rather than the temperature that caused the 

 gradual increase of soluble matter in every one of our different 

 series. To test this point we exposed one lot of soil to 120 for 

 ten hours, and upon analysis of the extract it showed only a slight 

 increase of soluble matter over the lot heated to 120 for two hours. 

 The intensity of the heat seems to be the controlling factor in ren- 

 dering the soil material more soluble. The organic matter, inor- 

 ganic matter and total nitrogen all seem to be affected by the heat, 

 but the organic matter and nitrogen show the greatest and most con- 

 sistent increases. The color, odor and degree of contamination 

 with Pyronema, Penicillium, etc., all show an increase parallel to 

 the soluble matter indicated by analysis. In the next section our 

 culture experiments show the same gradual change in the properties 

 of the heated soil extracts dependent upon the degree of heating. 



CHEMICAL NATURE OF THE SOLUBLE ORGANIC MATTER IN 



HEATED SOILS 



We have already reported that the extracts of heated soils are 

 acid to litmus, give the Molisch test for carbohydrates, reduce 

 Fehling solution, and give a precipitate with lead acetate solutions. 



14 Official and provisional methods of analysis. Bull. 107 (rev.), Bur. of 

 Chemistry, U. S. Dep't of Agriculture, Washington, 1908, p. 7, sec. (c). 



