of Gihl's's Theory of Surface-Concentration. 521 
We have here the remarkable phenomenon of the tension increasing 
with the temperature. But in similar experiments, using water alone 
instead of solution, there was a marked fall in the tension, as was to be 
expected, viz. : — 
Temperature. 
Tension in dynes per cm. 
16° C. 
41° C. 
67° C. 
48 
40-8 
371 
The increase in tension with temperature in the case of the glvco- 
cholate solution is to be accounted for, therefore, by partial " desorption "' 
having taken place ; that is, an increase of temperature in the case of the 
glycocholate solution decreases the quantity adsorbed, and hence, in 
accordance with the principle of Le Chatelier, adsorption must be accom- 
panied by heat evolution. 
Further experimental determination may make it possible to calculate 
the quantity of heat (Q) evolved per gram-mol. adsorbed by applying the 
equation 
(71ogK_ Q_ 
dt ~ KT 2 ' 
where K = ratio of concentration in surface layer to the bulk concen- 
tration. 
IV. Application to the Theoky of Dyeing. 
The various theories which have been advanced to account 
for the process of dyeing may be roughly divided into 
(1) Purely chemical combination or solid solution. 
(2) Purely physical surface effects (i. <?., Adsorption). 
(3) Partially surface effects and partially chemical 
combination. 
A great mass of evidence has been brought forward in 
support of these different views, but it is not proposed in this 
place to discuss them *. Mention should be made, however, 
of the most recent contribution, namely that of Freundlich f. 
whose results point very strongly to the absence of chemical 
combination, but leave it an open question as to whether 
dveing is au example of adsorption in the sense of Gribbs's 
theory. 
It is evidently essential to this view that dye-stuffs in 
solution should possess the property of lowering the inter- 
facial tension. This, of course, cannot be determined in 
* For an account of these various theories one may consult the work 
of W. P. Dreaper— ' Chemistry and Physics of Dveing ' (1906). 
t Freundlich, Zeitschr. Phys. Chem. vol. lix. p. 284 (1907). 
