196 



On the Physical Properties of Soil. 



Kinds of Earth. 



1000 grains of Earth on a surface of 50 square 

 inches, absorbed in — 



12 Hours. 



24 Hours. 



48 Hours. 



72 Hours. 





grains. 



grains. 



grains. 



grains. 





0 



0 



0 



0 



Calcareous sand 



2 



3 



3 



3 



vjypsuiii powutJi 



1 



] 



1 



1 



Sandy Clay . 



21 



26 



28 



28 



Loamy Clay . . 



25 



30 



34 



35 



oiiii uiay . . 



30 



36 



40 



41 



Grey pure clay . 



37 



42 



48 



49 



Fine lime 



26 



31 



35 



35 



Fine magnesia . 



69 



76 



80 



82 



Humus . 



80 



97 



110 



120 



Garden-mould . 



35 



45 



50 



52 



Arable soil . 



16 



22 



23 



23 



Slaty marl . 



24 



29 



32 



33 



General remarks. — 1. Excepting the siliceous sand, all kinds 

 of soil have the property of absorbing moisture from the atmos- 

 phere ; the slaty marl^ which, in regard to consistency and power 

 of containing water more nearly approaches the sand, distinguishes 

 itself more favourably than them in this respect ; the absorption is 

 seen to be generally the strongest in the clay-soils, especially when 

 they contain humus. 



2. Humus, of all the simpler constituents of soil, shows the 

 greatest power of absorption : in this respect, however, the kinds of 

 humus themselves furnish marked differences ; the pure vegetable 

 dried humic acid simply obtained from turf, in extended experi- 

 ments made by myself, absorbed moisture from the air far less 

 easily than that prepared from animal manure. 



3. The absorption is always the greatest at first ; the earths 

 always absorb less in proportion the more they gradually become 

 saturated with moisture, and they generally attain that point after 

 a few days ; if exposed to the sun-light, a portion of the absorbed 

 moisture becomes again vaporized ; in nature, a daily periodical 

 change in this respect appears to take place, which must have a 

 beneficial effect upon vegetation : the earths absorb moisture at 

 night which they partially give off again during the course of the 

 day. 



4. Fertile arable soils generally possess a great capability of 

 absorption ; still we must not conclude at once from the power of 

 absorption alone which a soil may manifest, as to its fertility, since 

 even clay soils without any humus absorb considerable moisture 

 from the air ; in the above experiments the pure sterile clay ab- 



