COLLOIDS. 27 



the colloid solution 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 

 substance 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 tw^> 

 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 



designated by cj. and 02, then it follows that = k where k is a constant. 1 



C2 



The first example where this la\v was shown to be correct was the divi- 

 sion of succinic acid between water and ether (BERTHELOT and JUNG- 

 FLEiscH 2 ). 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 =/b, where c\ and c 2 indicate the concentra- 



C<i 



tion of the solid body and in the solution; n and k are constants and indeed, n is 



, 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. 



