208 A. F. GUSTAFSON 



SUMMARY 



1. Oven-drying increased to a marked^degree the quantity of water-soluble 

 material removed from soil by 1 : 5 extraction with distilled water. 

 1^' 2. Air-drying swamp soils increased the water-soluble material and oven- 

 drying this air-dried soil brought about a still further increase. 



3. Storing soils for 9 weeks at 8 to 12°C. in open jars (in which water evapo- 

 rated was restored each week) or m sealed tubes in its original condition did 

 not markedly affect the total soluble material. Nitrification occurred in the 

 open jars, while nitrates decreased, as a rule, in the sealed tubes, 



4. Keeping soil at room temperature and optimum moisture content for 9 

 weeks did not materially affect the amount of soluble material, but there was 

 a slight increase in all soils except white silt loam. Keeping these soils sat- 

 urated at the same temperature, greatly increased the soluble material. In 

 the first case nitrification was active while in the latter, denitrification was 

 complete. 



5. Oven-drying decreased the nitrate-content of these soils. 



6. Wlien potassium nitrate in two concentrations was added to four grades 

 of quartz, it was not wholly recovered in one, or even two 1:5 extractions. 

 From the more dilute solution 67 to 80 per cent of the nitrate were recovered 

 in one extraction, while from the more concentrated, 77 to 95 per cent were 

 recovered. 



7. When potassium nitrate in a dish is heated in an oven at 105°C. for 8 

 hours, after being evaporated to dryness, a distinct loss of nitrate occurs. 



GENERAL CONCLUSIONS 



The literature cited and the experimental work here reported both bring out 

 one important point. They show the effect of drying at room temperature, 

 and heating in an oven at slightly above the boiling point, and in the autoclave 

 at various pressures and temperatures. In general, the quantity of soluble 

 inorganic constituents and organic matter is increased, while temperatures 

 above 100°C. reduce the quantity of nitrates. These facts indicate that in 

 planning soil biology studies, pot-culture or other greenhouse fertility inves- 

 tigations, the soils used should be kept under conditions strictly comparable 

 as to aeration, moisture content and temperature in order to avoid the intro- 

 duction of uncontrolled factors which might lead to erroneous conclusions. 



REFERENCES 



(1) AiTKEN, J. 1910 The fertilizing influence of sunlight. In Nature (London), v. 83, 



p. 37. 



(2) Allen, E. R., and Bonazzi, A. 1915 On nitrification. Ohio Agr. Exp. Sta. Tech. 



Bui. 7, p. 37. 



(3) Beaxjtviont, a. B. 1919 Studies in the reversibility of the colloidal condition of 



soils. N. Y. (Cornell) Agr. Exp. Sta. Mem. 21, p. 479-524. 



