222 



CAPACITY OF SOILS FOR HEAT. 



ascribes a greater power to the gases compressed or condensed 

 within the interstices of the soil. But the action of the air upon the 

 roots of vegetables is readily conceivable in soils of a loose nature, 

 especially if they have been sufficiently worked, without the necessity 

 of having recourse to such an explanation. 



Capacity of soils for heat. The quantity of heat which a soil will 

 receive, retain, or throw off in a given time, depends upon the con- 

 ducting power which it possesses. M. Schubler endeavored to 

 measure this power comparatively by measuring the rates of cooling. 

 In a vessel of the capacity of 595 cubic centimetres, or 234.2 cubic 

 inches, filled with the substance to be tried, a thermometer was 

 placed, with its bulb in the centre. The temperature having been 

 brought up to 62.5° C, (144.5^ Fahr.,) the time was noted which 

 each substance required to fall to 21.2° C, or about 70" Fahr., the 

 temperature of the surrounding air being 16.2° C, or about 61° Fahr. 



The general observations which these experiments suggest, are 

 that, for equal volumes, calcareous orsilicious sand possesses greater 

 powers of retaining heat than any «»f the other substances tried. 

 This fact explains the high temperature and the dryness which 

 sandy soils maintain even during the iiij^jht in summer. Humus is 

 obviously the substance which possesses the highest conducting 

 powers. 



Degrees in ivhich soils become heated under exposure to the sun. 

 There is no one who has not had occasion to observe tiie high tem- 

 perature which bodies acquire when exposed to the rays of the 

 bright sun. There are some, such as dry sand, slates, and certain 

 colored rocks, which become burning hot. It is by the heal of the 

 sun that the soil, before it is shaded by the leaves ami stems of plants, 

 ri.<es in temperature, and throws otrilie excess of moisfre which it 

 h;ui imbibed in the winter. Agrii-ullurists all know how diflerent 

 the degree in which this heating takes plane, even in soils that are 

 close to one another. A light-colored, moist, clayey soil will heat 

 much less than a dark-colored, calcareous, or sandy soil. The dif- 



