48 PHYSICAL CHEMISTRY IN BIOLOGY. 



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 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 



designated by c\ and c 2 , then it follows that = k where & is a constant. 1 



2 



The first example where this law was shown to be correct was the 

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

 FLEISCH 2 ). This law was also shown to be true for the division of 

 fi 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. For example, if we 

 are dealing with the absorption 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 absorbed fraction becomes continuously less so that 

 the absolute quantity taken up reaches a maximum which corresponds 

 to the greatest absorption ability of the solid body. This is expressed 



Ci n 



by the formula - =&, where Ci and c 2 indicate the concentration of the 



C 2 



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

 always >1. (If n=l then the formula would be =k and we would 



^2 



be dealing with a so-called solid solution). The process here treated 

 is called adsorption. 3 



APPLEYARD and WALKER 4 have studied the adsorption of organic 

 acids from aqueous and alcoholic solutions by means of silk; the divi- 



1 Nernst, 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. 



4 Journ. Chem. Soc., 69, 1334, 1896. 



