174 HOW CROPS FEED. 
containing brine concentrates the latter where the two 
are in contact, though the effect may be difficult to dem- 
onstrate. 
Defecating Action of Charcoal on Solutions,—Char- 
coal manifests a strong surface attraction for various 
solid substances, and exhibits this power by overcoming 
the adhesion they have to the particles of water when dis- 
solved in that fluid. If ink, solution of indigo, red wine, 
or bitter ale, be agitated some time with charcoal, the 
color, and in the case of ale, the bitter principle, will be 
taken up by the charcoal, leaving the liquid colorless and 
comparatively tasteless. Water, which is impure from 
putrefying organic matters, is sweetened, and brown sugars 
are whitened by the use of charcoal or bone-black.. In 
case of bone-black, the finely divided bone-earth (phos- 
phate of lime) assists the action of the charcoal. 
Fixing of Dye-Stuffs,—The familiar process of dyeing 
depends upon the adhesion of coloring matters to the fiber 
of textile fabrics. Wool steeped in solution of indigo at- 
taches the pigment permanently to its fibers. Silk in the 
same way fastens the particles of rosaniline, which consti- 
tutes the magenta dye. Many colors, e. g. madder and 
logwood, which will not adhere themselves directly to 
cloth, are made to dye by the use of mordants—substances 
~ like alumina, oxide of tin, ete.—which have adhesion both 
wo the fabric and the pigment. 
Absorptive Power of Clay.—These effects of charcoal 
and of the fibers of cotton, etc., are in great part identical 
with those previously noticed in case of sand and humus. 
Their action is, however, more intense, and the effects 
are more decided. Charcoal, for example, that has ab- 
sorbed a pigment or a bitter principle from a liquid, will 
usually yield it up again to the same or a stronger solvent. 
{n some instances, however, as in dyeing with simple col- 
ers, matters are fixed in a state of great permanence by 
