TRANSACTIONS OF THE SECTIONS. 



393 



tional to the tlifterence of densities, and the latter to the square 

 of this difference. 



The last term is the force of exosmose. It is proportional 

 to the efFort with which the fluid cylinders tend to penetrate 

 each other, independently of the action of the tube, and seems to 

 be a proper measure for the force with which the opposite fluids 

 tend to unite in the ordinary case of mixture. It is positive 

 when the attraction between the particles of the opposite fluids 

 exceeds the arithmetic mean between the attractions of the par- 

 ticles of the two fluids for particles of their own kind; is negative 

 when less than this mean, and of course vanishes in the case of 

 equality. 



When the force expressed by this last term is negative, the 

 fluid cylinders, instead of penetrating further into the opposite 

 Huid, will retreat into their respective fluids, and no mixture 

 will take place. This is probably the reason why some fluids, 

 such as oil and water, refuse to mix. 



The substances with which Dutrochet made his interesting 

 experiments were saccharine or gummy solutions on the one 

 hand, and water on the other. These fluids have a sufficient 

 tendency to mix for the purpose of carrying on the process ; 

 but that tendency being a very slow one (as any one may con- 

 vince himself by dropping a little treacle or a solution of gum 

 arable into a glass of water), the last term is probably very 

 small ; in which case the force ought to be very nearly propor- 

 tional to the difference of densities, which is the law observed 

 by Dutrochet. 



In support of that part of this theory which supposes the in- 

 terlacing of the internal cylinders, a passage is quoted from the 

 M^canique Celeste, in which La Place contemplates such an 

 arrangement*. But in whatever way the fluids be supposed to 

 mix in the interior of the tube, the same force of endosmose will 

 result, provided that the extremities of the tube are totally im- 

 mersed, one in one fluid and the other in the other, to a distance 

 within the tube not less than the sphere of sensible attraction. 



On Electro-chemical Decomposition. By Michael Faraday, 

 D.C.L. F.R.S. Professor of Chemistry in the Royal In- 

 stitutioti. 



In explanation of the present report of the subject brought 

 forward by Mr. Faraday at this time, it may be needful to say 

 that it forms part of his fifth series of Experimental Researches 



• Supplcm. au X^ Livrc, pp. 28, 29. 



