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LTV. Experimental and Theoretical Researches into the Figures 

 of Equilibrium of a Liquid Mass without Weight. — Eighth 

 Series. By Professor J. Plateau *. 



Researches into the causes upon which the easy development and 

 the persistence of liquid films depend. — On the superficial ten- 

 sion of Liquids. — On a new principle relating to the surf aces of 

 liquids. 



IN the last series of these researches, while discussing the 

 various processes of producing liquid films, I tried to make 

 it clearly understood that the production of such films always 

 depends upon the cohesion and viscosity of the liquid — the former 

 property opposing the rupture, and the second impeding the re- 

 lative motion of the molecules when the liquid has reached a 

 certain degree of thinness, and thus rendering any further atte- 

 nuation of it more slow. I concluded, in consequence, that the 

 property of undergoing extension into thin films must belong to 

 all liquids, and I tried to show that this is really the case. 



But if all liquids are capable of being spread out into thin 

 films, they nevertheless present important differences in the 

 degree of facility with which the films are formed, and in their 

 permanence when produced. For example, it is easy to blow 

 large bubbles at the end of a pipe with soap and water, but no 

 one would think of trying to do so with pure water. The easy ex- 

 tensibility of solution of soap and of some other liquids into thin 

 films of great size is generally ascribed to their viscosity; but I 

 find that viscosity, at least as commonly understood, plays only 

 a quite subordinate part in this facility of extension. In fact 

 experiments, which will be spoken of further on, show that the 

 viscosity of a solution of 1 part of Marseilles soap in 40 parts 

 of water, a solution with which bubbles can be blown more than 

 25 centims. in diameter at the mouth of a common tobacco-pipe, 

 is scarcely greater than that of pure water ; moreover one part 

 of the same soap in 500 parts of water is sufficient to give bub- 

 bles a centimetre in diameter ; and, lastly, the fat-oils, glycerine, 

 whether pure or mixed with water, treacle under the same con- 

 ditions, and solutions of gum-arabic of various degrees of con- 

 centration, liquids which are all of them more viscous than solu- 

 tion of soap, are absolutely incapable of being blow 7 n into bubbles 

 at the mouth of a pipe. We must consequently look elsewhere 

 for the cause of the phenomenon : this is what I do in the pre- 



* Translated from the Annales de Chimie et de Physique, S. 4. vol. xvii. 

 p. 260. For abstracts of the previous series see Taylor's Scientific Me- 

 moirs, vol. iv. p. 16, vol. v. p. 584; and Phil. Mag. (S. 4.) vol. xiv. p. 1, 

 vol. xvi. p. 23, vol. xxii. p. 286, vol, xxiv. p. 128, and vol. xxxiii. p. 39. 



