DEE Eee A OR ee Re IG ONS Oe EE ee OO OP Nd pe 
i vay 
S. W. Johnson on some points of Agricultural Science. 83 
the plant is to a destaiti extent independent of the soil, but again 
to a certain extent is affected by it. The absorption of poisons 
by fr is entirely abnormal and does not affect our statement. 
oes the grand Jaw of osmose (endosmose and exos- 
ont feed the plant out of such attenuated solutions, but, in all 
probability it aids the formation of these solutions. Graham has 
wn in the case of alum and bisulphate of potash that the 
unequal diffusive tendency of the members of a double salt is - 
powerful enough to decompose it, and he observed that solutions 
even of the neutral sulphates of pute and soda diffused their 
basic ingredients into lime-water, more rapidly — the acic 
these stable salts thus undergoing partial decomposition. 
The investigations of Henneberg and Stohmann Given cited, 
have proved that the absorbent power of a soil is not a purely 
chemical process, in the ordinary restricted sense; but is in part 
a physical phenomenon, i.e., it does not depe end — 
upon the presence in the soil, ‘of a certain amount of some pecu 
har kind of matter, but is also related to the eondition aa to the 
oe amount of acting surface of the various materials which 
> heirlooms oe Stohmann found that the dime of contuet be- 
tween a solution of an ammonia-salt and a soil did not affect 
the amount of eee mead es much adie natch taken up in 
They found too, that a given soil absorbed out of an equal 
@ of liquid very nearly the same amount of ammonia from 
uiva exe ge 
They observed however that the relative quantities of soil, 
water and the saline substance, affected the results ; thus from a 
stronger solution a greater absolute amount of ammonia was 
absorbed, while from a weaker solution a relatively greater 
quantity was taken up: and — isso more ‘was ab- 
also operate in ‘the soil to eases the Sitinibalsa affinities which 
are the prime cause of its absorptive properties. The chemical 
aflinity of silicate of alumina for the bases, (probably too that of 
oxyd of iron and alumina for some of the acids) is modified by 
the mass of the reacting substances and by that of their solvent; 
4 or in other words the cohesive force of the atoms of the com- 
