212 On the Physical Analysis of Soils. (Marcu, 
But when we cultivate a moist earth soaked with water, we have 
not merely the cohesion to overcome, but likewise the different 
degrees of adhesion to the plough. I examined this adhesion par- 
ticularly. J fixed plates of different substances and sizes to the 
arm of a balance, and determined their adhesion to the. different 
soils by the weight necessary to separate them. To be able to 
judge more accurately of this adhesive force, I reduced the results 
of the experiments to what would have taken place if the surface 
of the adhering plate had been a foot square. ‘The adhesion of 
clay is the greatest, that of sand the least. It is important to 
observe that wood adheres always more strongly than polished iron. 
1 repeated the experiment with several sorts of wood, particularly 
with beech. The cause must be ascribed to the different attractive 
force of substances, and likewise to their surfaces, which in wood 
always becomes more uneven when moistened, while that of iron 
remains the same. ‘This is the reason why oak-wood adheres more 
strongly to soils than beech. ‘These phenomena explain clearly the 
meaning of the terms heavy and light soil, founded entirely on the 
greater or less difficulty of overcoming the cohesive and adhesive 
forces. Thus a soil whose cohesion ina state of dryness is only 
100, will be easily ploughed; while a soil whose cohesion is 600 
will require a more fatiguing exertion. 
Columns eight and nine show the results of my comparative 
experiments on the evaporation of the soils. ‘To find the quantity 
of water which each kind allows to escape in a given time, and at 
a given temperature, I spread upon a thin plate of iron an even 
layer, containing a given quantity of the soil soaked with moisture, 
and expose it in a close room for four hours to the temperature of 
55°. The diminution of weight during that time gives me the 
quantity of moisture evaporated. or each experiment I employed 
the same quantity of soil, namely 200 grains, spread upon a sur- 
face of 10 square inches. 
I found in the same manner the difference of time which the 
different soils require to become dry to the same degree, or to lose 
the same quantity of water by evaporation. ‘This I could calculate 
with great exactness. 
The 10th column contains the comparative power of the different 
soils to absorb moisture from the atmosphere when exposed to it. 
For these experiments I always employed the soils in a state of 
complete dryness. I spread equal quantities of each soil upon 
equal surfaces (200 grains upon 10 square inches) which I placed 
upon stands under equal sized bell glasses, standing upon water to 
keep the air always uniformly saturated with moisture. I ascer- 
tained the increase of weight in 12, 24, and 48 hours. The 
absorption was greatest at first, and diminished in proportion as 
the soils imbibed humidity, and ceased entirely after some days, ’ 
when they were saturated with it. The absorption of humus sur- 
passes that of all the others, even of magnesia. 
Columns 11 and 12 show the proportion of oxygen gas absorbed 
