ORIGIN OF THE SMALL BUBBLES OF FROTH. 205 



for stability. Subsequently, in 1878, the matter was 

 independently discussed by Willard Gibbs, 1 who devotes, 

 to the consideration of the general problem, a section of 

 his famous Essay on the Equilibrium of Heterogeneous 

 Substances. 



To Lord Rayleigh we are not only indebted for an 

 account of the frothing of liquids, contained in a lecture 

 on "Foam," 2 given at the Royal Institution in 1890, but 

 we also owe to him, as a result of his experimental 

 researches in connection with surface forces, the knowledge 

 which affords a basis of fact to explanations advanced from 

 theoretical considerations. 



So far as I am aware, no explanation has yet been given 

 why, with vigorous agitation, the bubbles are so much 

 smaller and more numerous with a slightly concentrated 

 solution than when a pure solvent is used, and it was to the 

 discovery of the origin of these small bubbles that my own 

 observations have been directed. The phenomenon is a 

 striking one, and I feel that an explanation may have 

 occurred to others, but no reference to its publication can 

 be found. 



The question of the origin is closely connected with that 

 of the durability of the bubbles, and in order to present 

 the facts on which depends the description of the way 

 these bubbles are produced, I propose, in the first instance, 

 briefly to recapitulate the explanation which has been given 

 of the durability of froth. 



II. Durability of Froth.— The surface tension of a pure 

 liquid has a value which varies only with the temperature. 

 The association of such a characteristic, with the tension of 



1 G-ibbs, Trans. Conn. Acad., Vol. in, p. 467, 1878 ; Scientific Papers, 

 Vol. i, p. 300. 



2 Lord Rayleigh, Proc. Hoy. Inst., Vol. xm, 1890 ; Scientific Papers 

 Vol. in, p. 351. 



