ORIGIN OF THE SMALL BUBBLES OF FROTH. 



207 



It has been previously mentioned that water contamin- 

 ated with a trace of insoluble oil gives a froth which is 

 strikingly persistent compared to that of pure water. The 

 durability here can only be due to the presence, on the 

 surfaces of the bubbles, of a layer of oil, which must be 

 excessively thin, judging from the immense number of 

 bubbles which a single drop of oil can render stable. 



That sucha surface layer possesses the property necessary 

 for it to ensure durability has been fully demonstrated 

 by Miss Pockels and by Lord Rayleigh, both of whom 

 measured the variations in the tension of a water surface 

 caused by changes in the thickness of a contaminating 

 pellicle of oil. 



To illustrate the nature of the results which were 

 obtained, figure 1 has been copied from a publication by 

 Lord Rayleigh, 1 the scales to which the abscissae and the 

 ordinates are drawn being supplied from numbers given in 

 the paper. 



Fig. 1. 



10 



60 





A 











n 



it 

 ft 













AM of {ayCfts of 



otlx /0 7 







7 Z 5 4 c&vitom&bi&i 



Relation between the surface tension and thickness of the layer of oil 

 %n the case of a water surface contaminated with a pellicle of castor oil. 

 From a paper by Lord Rayleigh. 1 



1 Lord Rayleigh, Phil. Mag., Vol.XLVii,p. 321, 1899; Scientific Papers, 

 Vol. in, p. 415. 



