126 Prrston—On the Continuity of Isothermal Transformation, &c. 
the external work done is greater than that performed in passing along CD, but 
this is compensated by the destruction of the surface film. Thus, along BMC, 
there is on the whole a creation of surface film with less external work, and 
along CND there is destruction of surface film accompanied by increased external 
work—the excess in the former being equal to the defect in the latter. 
In conclusion, it may be remarked, that the views here put forward seem to 
have an important bearing on many interesting questions connected with the 
boiling points of liquids, and the manner in which they are affected by the 
presence of dissolved salts. It is sufficient to merely point out, at present, that 
obviously any operation which increases the surface tension of the film separating 
a liquid from its own vapour, will also raise the boiling point, for when 7 is 
increased, a greater vapour pressure a within a bubble will be required in order 
to enable it to expand against a given external pressure. This prediction of the 
theory appears to be in accordance with the observed facts. 
