On the Physical Properties of Soil. 



201 



tin-plate^ and having heated them to the same temperature, we 

 observe,, by means pf a thermometer inserted in the middle of 

 the mass, the time they respecti^ ely require to cool down again 

 to the original degree of temperature. 



The several earths gave me the following differences in this 

 respect. I heated 30 cubic inches of earth in each case up to 

 1444° F.,. and observed in a close room, having the temperature of 

 61:^° F., the time which they respectively required to cool down 

 to 701° F. ; and having set down the power of retaining heat in 

 the case of calcareous sand^ as equal to 100, I reduced the 

 remainder to this standard. 



Kinds of Earth. 



Power of retain- 

 iug Heat, that of 

 Calcareous Sand 

 being =100.0 



Length of time required by 30 

 Cubic Inches of Earth to cool 

 down from a temperature of 

 Uii^ to 70-1° F. in a surround- 

 ing temperature of 61i°. 



Calcareous sand . 



100.0 



in 3 hours, 30 min. 



Siliceous sand . 



95.6 



3 





20 — 



Gypsum powder . 



73.8 



2 





34 — 



Sandy clay 



76.9 



2 





41 — 



Loamy clay 



71.8 



2 





30 — 



Stiff clay, or brick-earth 



68.4 



2 





24 — 



Grey pure clay 



66.7 



2 





19 — 



Fine lime .... 



61.3 



2 





10 — 





49.0 



1 





43 — 



Fine magnesia . 



38.0 



1 





20 — 



Garden-mould 



64.8 



2 





16 — 



Arable soil 



70.1 



2 







Slaty marl .... 



93.1 



3 





26 — 



General Remarks. — 1. The sands possess the greatest power 

 of retaining heat when the earths are compared in equal quanti- 

 ties according to bulk ; hence may be explained the dryness and 

 heat of sandy districts in summer. Such districts, after sunset, 

 must also maintain a higher temperature and for a longer time 

 than others the soils of which possess a smaller power of retaining 

 heat ; and the slight power which sandy soils possess of containing 

 water, in consequence of which but little warmth is abstracted 

 from them by evaporation, must still further increase the degree 

 of this property. 



2. The slaty marl stands next to sands in regard to its power of 

 retaining heat ; and having at the same time a greater power of 

 containing water, this circumstance must contribute to its fer- 

 tility. 



3. Among the ordinary constituents of soil, humus is that 

 which has the least power of retaining heat. Turf-soils, too, 

 abounding in humus, grow warm but slowly, because they are 



