ABSORPTION OF HEAT 8i 



Soil Thermometry. 



The measurement of soil-temperature at different 

 depths is sometimes resorted to in connection with the 

 characterisation of different soils. Field experiments on 

 the subject require special attention and special forms 

 of thermometers, but the rate of absorption of heat by 

 a soil may be measured and compared with a standard 

 soil by means of a simple apparatus. 



60. Absorption of Heat by Soil. 



A cubical metal box about 4 inches square is filled 

 compactly with the " air-dried fine earth " (64) of the 

 soil to be examined. The box should be covered with 

 felt to prevent access of heat except at the exposed 

 surface, and should be provided with small openings at 

 different depths to allow of the insertion of thermometers. 

 The open end is then exposed for a few hours to the 

 direct rays of the sun, and the temperature at various 

 depths noted at intervals. 



The rate of heating should be compared, in the 

 cases of a sandy and a heavy soil, both in the dry and 

 moist condition, and the results plotted out graphically. 

 Dark and light coloured soils should also be compared. 

 The temperature of the surrounding air must be noted, 

 and the conditions, as far as possible, chosen identically 

 in all the experiments. For this reason it is as well to 

 have several similar boxes in use at the same time. 



Plocculation and Deflocculation of Clay. 



The very fine particles which compose that fraction of soil 

 known as clay, may, in certain circumstances, be aggregated or 

 coagulated to form larger granules, which themselves act as 

 separate soil particles. This phenomenon, termed flocculation^ is 

 most important from the point of view of cultivation of clay soils, 

 since it is highly desirable to obtain the soil in a coarse-grained 



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