198 On the Physical Properties of Soil. 



Kinds of Earth. 



Absorbed in 

 the dry state. 



In the wet state. 



Absorption in 30 days, by 1000 grains of 

 Earth, from 15 Cubic'inches of Atmospheric 

 Air containing 21 per cent, of Oxygen. 







Per cent. 



Cubic inches. 



Grains. 



Siliceous sand . . 



0 



1 . 6 



0.24 



0.10 



Calcareous sand. . • 



0 



5.6 



0.84 



0.35 



Gypsum powder . . 



0 



2.7 



0,40 



0.17 



k/CtlXLi Y ^A-dj • • # • 



0 



9.3 



1.39 



0.59 



T.namv plav 



Xj\jctijLxy %^x<xy « • • 



0 



11.0 



1.65 



0.70 



Stiffplav ni* Tiriolf-pavtli 



k7till Uld y 5 KJL UX1L«JY cell til 



0 



13.6 



2.04 



0.86 



Grey pure clay 



0 



15.3 



2.29 



0.97 



Fine Lime .... 



0 



10.8 



1.62 



0.69 



Magnesia . . , . 



0 



17.0 



2.66 



1.08 



Humus .... 



0 



20.3 



3.04 



1.29 



Garden-mould . 



0 



18.0 



2.60 



1.10 



Arable soil 



0 



16.2 



2.43 



1.03 



Slaty Marl .... 



0 



11.0 



1.65 



0.70 



General remarks, with further experiments on this property. — 

 All the earths lose on drying the property of absorbing oxygen from 

 the air, but regain it in the same proportions as before on being 

 moistened ; if covered about a quarter of an inch deep with water 

 in the closed vessel, the absorption takes place in the same 

 manner ; water alone, however, in the same quantity, and in the 

 same vessels, absorbs only a very small portion per cent, in the 

 same time, a clear proof that it is the earths themselves which 

 induce this process in a different proportion. 



2. Humus, of all the ordinary earths, exhibits the greatest 

 degree of absorption of oxygen ; the clays approach nearly to it ; 

 sand shows the least; fertile earths rich in humus absorb in ge- 

 neral more than others which are poorer in humus and clay ; the 

 included air standing over them becomes at last so poor in oxygen 

 that lights would become extinguished, and animals die in it. 



3. In the mode of absorption, there is an essential difference 

 between humus and the inorganic earths ; humus combines 

 partly with the oxyen in a strictly chemical sense, and assumes a 

 state of higher oxygenation, in consequence of which there is 

 formed also some carbonic acid ; the inorganic earths, on the con- 

 trary, absorb the oxygen gas without intimate combination ; if 

 dried in a higher temperature than from 167° to 189J° F., the 

 oxygen escapes again, but they re-absorb it on being moistened ; 

 this experiment may therefore be many times repeated with the 

 same earth. 



4. In the case of earths which are frozen, or covered with a sur- 

 face of ice, no absorption of oxygen takes place, any more than in 

 the case of dry earths j in a moderately warm temperature, varying 



