Wilson — Changes in Soils brought about by Heating. 519 



Fis. 3. 



In this, as ia the previous set of experiments, the solutions showed a 

 marked range in coloration. The electrical conductivity and depression of 

 freezing-point showed a considerable increase in the solutions obtained from 

 soil heated to the higher temperatures. The greater regularity of increase in 

 these solutions was probably due to the method of extraction, which enabled 

 soluble matter to be taken from all parts of the soil sample. Several samples 

 were heated carefully at the lower temperatures, and the electrical con- 

 ductivities and depressions of freezing-point of the extracts were determined. 

 These measurements show the fluctuations that may be expected in extracts 

 from soil subjected to identical treatment. It may be remarked that the 

 electrical method is the more sensitive for detecting small changes. 



Summary. 



The results of these experiments show that at any rate part of the 

 increased productivity of heated soil may be due to the increase in soluble 

 matter induced by heating, and to the change in soil-texture, which has a 

 remarkable effect on the retention of water by the soil. 



The increase in the amount of soluble matter is seen in : — 



(ffl) the range of coloration of the solutions extracted from soil heated at 



different temperatures ; 

 (5) the increase in electrical conductivity of the solutions ; 

 (c) the increased depression of freezing-point found in extracts from soil 

 heated at the higher temperatures. About half the total depression 

 throughout the experiments is due to electrolytes. 



