304 pn HOW CROPS FEED, 
liquid that flows out at the lower opening appears almost 
odorless and colorless, and has entirely lost its original 
properties.” After instancing the facts that wells situ- 
ated near dung-pits are not spoiled by the latter, and that 
the foul water of the Seine at Paris becomes potable af- 
ter filtering through porous sandstone, Bronner contin- 
ues: ‘These examples sufficiently prove tlat the soil, 
even sand, possesses the property of attracting and fully 
_ absorbing the extractive matters so that the water which 
subsequently passes is not able to remove them ; even the 
soluble salts are absorbed, and are only washed out to a 
small extent by new quantities of water.” 
It was subsequently observed in the laboratory of 
Liebig, at Giessen, that water holding ammonia in solu- 
tion, when poured upon clay, ran through deprived of 
this substance. Afterward, Messrs. Thompson and Hux- 
table, of England, repeated and extended the observa- 
tions of Bronner, and in 1850, Professor Way, then 
chemist to the Roy. Ag. Soc. of Eng., published in the 
Journal of that Society, Vol. XI, pp. 315-379 an account 
of a most laborious and fruitful investigation of the sub- 
ject. Since that time many chemists have studied the 
phenomena of absorption, and the results of these labors 
will be briefly stated in the paragraphs that follow. 
There are two kinds of absorptive power exhibited by 
soils. One is purely physical, and is the consequence of 
adhesion or surface-attraction, exerted by the particles of 
certain ingredients of the soil. The other is a chemical 
action, and results from a play of affinities among certain 
of its components. 
) The physical absorptive power of various bodies, in- 
cluding the soil, has been already noticed in some detail 
(pp. 161-176). In experiments like those of Bronner, 
just alluded to, the absorption of the coloring and odor: 
ous ingredients of dung-liquor is doubtless a physical 
process. These substances are separated from solution by 
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