ABSORBENT POWER OF SOILS. 173 
action of oil of vitriol on sugar, when placed in ten times 
its quantity of solutions of various salts (containing about 
$ per cent of solid matter) absorbed of sulphates of soda 
and ammonia, and chlorides of calcium and ammonium, 
about 2 per cent; of sulphate of potash 4 per cent; and of 
phosphate of soda 10 per cent. Schumacher also noticed 
that sulphate of potash is able to expel sulphate of ammo- 
nia from humic acid which has been saturated with the 
latter salt, but that the latter cannot displace the former. 
In Schumacher’s experiments, pure water freely dissolved 
the salts absorbed by the humic acid. 
Explanation.—Let us consider what occurs in the act 
of solution and in this separation of soluble matters from 
a liquid. The difference between the solid and the liquid 
state, so far as we can define it, lies in the unequal cohe- 
sion of the particles. Cohesion prevails in solids, and op- 
poses freedom of motion among the particles. In liquids, 
cohesion is not altogether overcome but is greatly weak- 
ened, and the particles move easily upon each other, 
When a lump of salt is put into water, the cohesion that 
otherwise maintains its particles in the solid state is over- 
come by the attraction of adhesion, which is mutually ex- 
erted between them and the particles of water, and the 
salt dissolves. If now into the solution of salt any in- 
soluble solid be placed which the liquid can wet (adhere 
to) its particles will exert adhesive attraction for the par- 
ticles of salt, and the tendency of the latter will be to 
concentrate somewhat upon the surface of the solid. 
If the solid, thus introduced into a solution, be exceed- 
ingly porous, or otherwise present a great amount of sur- 
face, as in case of sand or humus, this tendency is propor- 
tionately heightened, and a separation of the dissolved 
substance may become plainly evident on proper examina- 
tion. When, on the other hand, the solid surface is rela- 
tively small, no weakening of the solution may be percep- 
tible by ordinary means. Doubtless the glass of a bottle 
