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COLLOIDS. 27
the colloid BOlution as a homogeneous fluid of suspended solid or fluid
particles, then in the " solution " there occur at least two special con-
stituents] separated from each other—the colloid particles and the sol-
vent. This is expressed as follows: the system contains two phases.
The solvent is often more correctly called the dispersion means and the
colloid particles called the disperse phase. If to such a system a new
sul stance is added, then the reaction which follows, depends essentially
upon the division of the new substance between the two phases. In
regard to the possible division two cases will be presented:
1. The process can be similar to the division of a soluble substance
between two solvents. If a substance is brought in contact with two
solvents at the same time, then it divides itself so that the relation
between the concentration in the two solvents remains the same but
independent of the total quantity of the dissolved substance. If the
quantity of substance in each 100 cc. of the two solutions 1 and 2 is
Cl
designated bv ci and c-2, then it follows that —=k where k is a constant. 1
C-2
The first example where this law was shown to be correct was the divi-
sion of succinic acid between water and ether (Berthelot and Jung-
fleisch -’.). This law was also shown to be true for the division of
a gas between a gaseous and a fluid phase, i.e., for the absorption of a
gas in a fluid (Henry’s law of absorption). The conditions for the cor-
rectness of this law are that the temperature remains the same in experi-
ments with different quantities of substance as well as that the substance
has the same molecular size in the two phases.
2. In those cases where finely divided solids take up dissolved sub-
stances or gases the division is generally not independent of the total
quantity of the dissolved substance or of the gas. This is often called
adsorption.3
For example, if we are dealing with the adsorption of a
dissolved substance by a finely divided solid occurring in a solution,
then a greater percentage is taken up from a dilute solution than from a
concentrated one. On increasing concentration the adsorbed fraction
becomes continuously less so that the absolute quantity taken up reaches
a maximum which corresponds to the greatest adsorption ability of the
solid body.
This is expressed by the formula — = k, where Ci and c2 indicate the concentra-
tion of the solid body and in the solution; n and k are constants and indeed, n is
’Nenut, Zeitschr. f. physik. Chem., 8, 110 (1891).
2 Ann. Chim. phys. (4>. 26. 396 (1872).
3
It must be remarked that in the older literature oftentimes no difference was
made between adsorption, and absorption, in which case both processes were included
under the name absorption.
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