450 Action of the Atmosphere upoji ncwhj-deepened Soil. 



vegetable matter or not. The following results obtained by Leslie 

 clearly show this effect in regard to several bodies : — 



Degrees of Moisture 

 Kinds of Earth thoroughly Dried. absorbed from Air 



at about 6U" Fahr. 



Clay very highly torrefied 8 



„ strongly roasted 35 



Pipe-clay . . 85 



Silica very highly torrefied, , . . . . 19 



„ soaked in water and dried after high torro-1 qr 



faction J "^ 



„ in its natiyal state 40 



Whinstone very liigldy torrefied 23 



,, in its natural state 80 



„ in a criirahling state 86 



,, reduced to mould 92 



Carbonate of lime 70 



Shelly sea-sand 70 



Sea-sand from a sheep-walk 78 



,, cultivated 85 



Carbonate of magnesia 75 



Alumina 84 



Garden mould 95 



The substances were dried thoroughly and introduced imme- 

 diately into a phial with a close stopper ; the powder having 

 undergone that preparation was thrown into a very large wide- 

 shaped bottle, and shut up till it had attracted its share of hu- 

 midity from the confined air ; a delicate hygrometer being now 

 let down into the bottle indicated the measure of the effect pro- 

 duced by absorption. (^Leslie on Heat and 31oistnre.) Leslie 

 looked upon this power as exactly analogous to that of the con- 

 centrated acids and deliquescent salts. 



As the greater the power of a soil to contain water, the more 

 has it, in general, the property of absorbing moisture when dry, 

 and gaseous matter when in a moist state, from the air, I have 

 extracted the following- results from the examination of German 

 soils by Geiger, Sprengel, and Schubler, in regard to their power of 

 containing water, and have arranged them in a tabular form (p. 451), 

 so that the facts contained in it may more readily catch the eye. 



It will be seen, therefore, from all the results shown in the Table, 

 that this power of absorbing moisture, oxygen, and probably other 

 gases, is most highly developed in humus ; that clay also stands 

 high in the list ; and that siliceous or quartz sand is very clearly de- 

 ficient in this respect ; — that much moreover depends upon the 

 mechanical condition, for whatever tends to reduce the substance 

 to a state of tine division exalts the absorbent power. Davy, for 

 instance, found that 1000 grains of coarse sand, dried at 212^ F., 

 absorbed from a moist atmosphere only eight grains of moisture, 

 whereas the like quantity oi fine sand, under the same treatment, 



