70 Power of Soils to Absorb Moisture. 
diminishes the retaining power. This is more plainly exhibited 
in sand and sandy soils than in others. 
It may be stated in general terms that the absorbing is as the 
retaining power; and the retaining, as the amount of water a soil 
is susceptible of taking up. We owe the first experiments on the 
relative power of soils to absorb moisture to Sir. H. Davy.* He 
made a sufficient number of observations to show that the power 
of soils to absorb moisture was intimately connected with their 
fertility. His method of proceeding was the following: He took 
1000 parts of each of several kinds of soil, dried at 212,° and 
containing different quantities of organic matter, and exposed 
them to an atmosphere saturated with moisture at 62°, and let 
them remain a given time, when they were found to have increased 
in weight in proportion to the organic matter they contained. 
He found that the different constituent parts of soils absorbed 
moisture with different degrees of energy. Thus vegetable sub- 
stances more absorbent than animal; animal substances more so 
than compounds of alumina and silica; and these more absorbent 
than carbonates of lime and magnesia. 
These observations have been confirmed, with some modifica- 
tions, by Prof. Emmons,t who has further shown that the absorb- 
ent power is as the retentive. It was the previous opinion that 
clays possessed a greater absorbing power than the marls, which 
he found to be incorrect. He says: " It was observed that marls, 
or the finely divided calcareous compounds, are quite powerful 
absorbers and retainers of water, being even superior to clay or 
argillaceous compounds, or to alumina in a state of great purity. 
This result was quite unexpected, as the common and prevailing 
opinion is, and has been, that clays are the most active and ener- 
getic in their powers of absorbing and retaining moisture. 
" In accordance, then, with these observations, we found that 
the materials which are the most influential in soils, may be 
arranged in the following order, when their relations to water or 
• Second edition of Sir H. Davy's Lectures on Agricultural Chemistry, 1814. 
t Agricultural Report of New York, vol. i., page 352. 
