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COLLOIDS. 29
solved bodies, and for this reason the ads >rbed substance lowers the
surface tension of the solid-fluid, and indeed, the more the greater con-
centration in which it occurs. That especially carbon and colloid sub-
stances are adsorption bodies lies in the fact that they have an especially
large surface due to their finely divided state or porosity, which there-
fore, cet. par., must give them a great surface energy.
That proteins, on precipitation, carry down other bodies with avidity
is well known; inorganic hydrogels also take up dissolved substances
with energy. The curves obtained for the latter process by van Bem-
melen x
show a close analogy with the characteristic curves for the
adsorption compounds. It often occurs that the body taken up homo-
geneouslv saturates the hydrogel, in which case — = k, and a sort of
solid solution is the result. In certain cases, undoubtedly, chemical
combinations with quite positive conditions are formed.
The precipitation of colloids by electrolytes has also been discussed
by Freundlich 2
from the standpoint of the adsorption hypothesis.
Thus, for the precipitation ability of an electrolyte, the electric charge
of the precipitating ion comes first into consideration and secondly, the
ability of the precipitating colloid to adsorb the same. According to
Moore and Roaf3
the salts of the red corpuscles are retained as adsorp-
tion compounds (adsorpates) by the proteins.
Thus far only the adsorption of crystalloids has been considered.
Colloids are also taken up by solid substances or by other colloids. Still in
these cases the conditions are more complicated than in the above-
mentioned adsorption phenomena, as the combinations formed are in special
cases irreversible or gradually become irreversible. It is well known that
carbon takes up colloidal colored substances, and we have numerous exam-
ples of the combination of dissolved colloids with solid colloids in technology.
Biltz 4
has been able to show that many dyeing processes are to be
considered as adsorption phenomena, and later Freundlich and Losev 5
have measured the adsorption of basic and acid pigments by carbon
and also by fibers (wool, silk, cotton), and have shown the correspondence
of the two processes. With the basic pigments, which were used as
salts, a splitting occurred into a pigment base, which was taken up by
the fibers as well as by carbon, and an acid which quantitatively remained
behind. This is similar to the cleavage which precipitating electrolytes
undergo in the precipitation of the suspension colloids (see page 26).
1
Zeitschr. anorg. Chem., 23, 111, 321 (1900).
2
Zeitschr. f. Chem. u. Ind. d. Koll., 1, 321 (1907).
3 Bioch. Journ., 3, 55 (1908).
4 Ber. d. d. chem. Gesellsch., 37, 1766 (1904); 3S, 2963, 2973, 4143 (1905).
5 Zeitschr. f. physik. Chem., 59, 284 (1907).
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