Permeability ioi 
lines will be obtained if the adsorption equation holds; this is shown 
to be approximately the case. 
It follows from the adsorption equation that as the concentration 
of the solution increases the quantity adsorbed increases, but the 
quantity relative to the concentration decreases. For example, if 
finely divided charcoal is added to solutions of substances, adsorp¬ 
tion generally takes place at the surface of the charcoal. Now if 
charcoal is added to a solution of acetic acid in water, when the 
concentration of the acetic acid at equilibrium is o*oi8, the quantity 
adsorbed per unit mass of adsorbent is 0*467; when the equilibrium 
concentration is 2*79, the quantity adsorbed per unit mass of ad- 
X 
sorbent is 376. That is, although — in the adsorption equation has 
increased from 0*467 to 3*76, its value relative to the concentration 
of the solution, has decreased from 26 to 1*35. 
As surface tension decreases with rise in temperature so adsorp¬ 
tion also is less the higher the temperature. As the adsorption at 
a temperature 6 + 10 is thus a fraction of what it is at 6 , adsorption 
has a fractional temperature coefficient, if the temperature coefficient 
of a process is regarded as the number by which the value of the 
process at one temperature has to be multiplied in order to give the 
value of the process at a temperature 10 centigrade degrees higher. 
The temperature coefficient is then generally denoted by the symbol 
< 2 10 - When the process, as in the case of adsorption, is lessened with 
rise of temperature, the temperature coefficient is less than unity. 
Such processes are often spoken of as having a negative temperature 
coefficient. This is not necessarily a misuse of the term negative, for 
by “temperature coefficient” is sometimes understood the quantity, 
or a multiple or fraction of a quantity, which has to be added to 
the value of a process for a rise of i° C. This temperature coefficient 
is often denoted by the symbol a. It is unfortunate that the term 
“temperature coefficient” should be used in these two senses. 
It must be noted that although adsorption decreases with rise 
of temperature, the rate at which adsorption is brought about in¬ 
creases. This is due to the fact that the rate of adsorption must 
depend on the rate at which the adsorbed substance can diffuse 
through the medium containing it. It is therefore to be expected 
that the rate of adsorption would have a temperature coefficient not 
far different from that for rate of diffusion, and this has been shown 
by Bayliss (1911) to be the case with adsorption of congo red by 
filter paper. 
3~5 
