S34 HOW CKOPS 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 

 tlie foul water of the Seine at Paris becomes potable af- 

 ter filtering through porous sandstone, Bronner contin- 

 ues: "These examples sufficiently prove that 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 nev) quantities of waterP 



It was subsequently observed in the laboratory of 

 Liebig, at Giessen, that water holding ammonia in solu- 

 tion, when poured upon clay, lan through deprived of 

 this substance. Afterward, Messrs. Thompson and IIux- 

 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. XL, pp. 313-379 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 i)lay of affinities among certain 

 of its components. 



I The physical absorptive power of various bodies, in- 

 cluding the soil, has been already noticed in some detail 

 (pp. lGl-176). In experiments like those of Bronner, 

 just alluded to, the absorption of the coloring and odor- 

 ons ingredients of dung-liquor is doubtless a physical 

 process. These substances are separated from solution by 



