On the Physical Properties of Soil. 



191 



ascertain the weight of the whole ; we suffer it to remain for several 

 hours in a closed room to evaporate, and again weigh it to ascertain 

 the quantity of water evaporated during the time ; if we make the 

 experiment with many earths at once^ we shall be able to institute 

 a comparison among them with the greatest certainty in reference 

 to this point. To obtain accurately the quantity of water con- 

 tained in the earth at the commencement of the experiment, we 

 afterwards dry it perfectly in an artificial heat, and thus easily re- 

 duce the quantity of evaporated water to hundredth parts of that 

 contained in the earth. 



Grains. 



Let the weight of a wet earth be 310 



The weight of the same earth after 24 hours .... 260 

 The weight of the perfectly dried earth 200 



Therefore'the amount of water evaporated in 24 hours will be 50 

 And the water in the earth at the beginning of the experiment 110 



Since^ in this case, 50 of the 110 parts of the water taken up 

 have evaporated, the amount of water vaporized from 100 parts 

 will be 4 5.*5 Mparts. The following table contains the results 

 of the experiments which I obtained, in reference to this pointy 

 with 200 grains of the several earths at a temperature of 65|° : 

 they were spread out over a surface of ten square inches. The 

 second column of the table contains in one view the portions of 

 time in which the several earths respectively became dry under 

 exposure to the same temperature ; I did not require a perfect 

 state of dryness, as this, at a temperature of 65J° F. and in the 

 open air^ could not be expected. 





Capability of drying. 





Evaporation 



Times required 



Kinds of Earth. 



from 100 parts 



for 90 parts of water 





of absorbed 



to evaporate 





water, at 65^= F. 



(at 65|» F.) from 





in 



100 







4 hours. 



parts absorbed. 





Parts. 



Hours. Minutes. 



Siliceous sand . , 



88.4 



4 



4 



Calcareous sand , , . 



75.9 



4 



44 



Gypsum powder 



71.7 



5 



1 



Sandy clay .... 



52.0 



6 



55 



Loamy clay . . ... 



45.7 



7 



52 



Stiff clay, or brick earth . 



34.9 



10 



19 



Pure greyj'lay . 



31.9 



11 



17 



Fine lime .... 



28.0 



12 



51 



Humus ..... 



20.5 



17 



33 



Magnesia . , . . 



10,8 



33 



20 



Garden-mould • • . 



24.3 



14 



49 



Arable soil .... 



32.0 



11 



15 



Slaty marl .... 



68.0 



5 



53 



