370 Lord Ray lei gh on Experiments 



formerly recorded* with soapy water have shown that the 

 ratio of tensions for pnre water and for solution of camphor 

 are the same at the first moment of the formation of a free 

 surface as when the measures are conducted statically. 



Saponine and Soap. 



A strong infusion of horse-chestnuts allowed excellent 

 bubbles to be blown, up to 4 inches or more in diameter. 

 When the interiors of equal bubbles of soap and of saponine 

 Avere brought into communication, the latter contracted and 

 the former expanded, showing that the tension of the sapo- 

 nine film was the greater. In order to obtain equilibrium, 

 the diameter of the saponine bubble required to be about half 

 as great again as that of the soap bubble. These saponine 

 bubbles exhibited the characteristic wrinkling, when caused 

 suddenly to contract by withdrawal of part of the contained air. 



The foaming of Highland waterfalls is doubtless attributable 

 to dissolved vegetable matter. In the autumn of 1890 I had 

 an excellent opportunity of observing these effects in the case 

 of the river Creed at Stornoway. By the coalescence of 

 smaller ones hemispherical bubbles of remarkable size, up to 

 a foot or more in diameter, were frequently formed, and en- 

 dured for a few seconds; and yet not the smallest bubble 

 could be blown from a tobacco-pipe. However, by collecting 

 some of the foam and allowing it to subside, which took a 

 good while, I obtained liquid from which bubbles could be 

 blown with a pipe up to 4 inches diameter. But these bubbles 

 behaved like soap, and not as had been rather expected, like 

 saponine, remaining perfectly light and smooth when the 

 included air was rapidly withdrawn. 



Separation of Motes. 



In the course of some experiments last year, in illustration 

 of Sir G. Stokes's theory of ternary mixtures, I had prepared 

 an association f of water, alcohol, and ether, in which the 

 quantity of alcohol was so adjusted that the tendency to 

 divide into two parts was almost lost. As it was, division took 

 place after shaking into two nearly equal parts, and these 

 parts were of almost identical composition. On placing the 

 bottle containing the liquids in the concentrated light from an 



* Proc. Roy. Soc. March 1890. 



f Association is here employed as a general term denoting the juxta- 

 position of two or more fluids/ Whether the result is a mixture depends 

 upon circumstances. 



