﻿Surf ace-Tension and Osmotic Pressure of Solutions. 271) 



much below that which has been found to be safe in these 

 experiments. 



in the experiments of Threlfall the sign of the term 

 depending on time was found to be negative. In some of my 

 earlier experiments it appeared to be negative, but this was 

 traced to irregularity in the working of the compensator ; and 

 the effect has always been positive since the Clark cells have 

 been used in the place of Leclanche, vide § 5. 



XXXII. On a Relation between the Surf ace-Tension and 

 Osmotic Pressure of Solutions. By B. Moore, M.A., 

 Exhibition Scholar, Queen's College, Belfast* . 



AT present the cause of osmotic pressure in solutions is 

 unknown, although the laws regulating it and connecting 

 it with the kindred solution phenomena, viz. the lowering of 

 the freezing-point and of the vapour-pressure, have been well 

 worked out within the last few years. 



This paper is an attempt to show that it may be produced 

 by difference in surface-tension acting along the exceedingly 

 fine capillary openings of almost molecular dimensions which 

 place the solution in connexion with its solvent in the pores 

 of the semipermeable wall which separates them. 



If two liquids which mix and have a different surface- 

 tension be placed each in one of two wide tubes communi- 

 cating beneath by a capillary, as shown 

 in the figure, there is a surface over 

 which capillary action will take place, 

 between each liquid and the wall of 

 the tube containing it. Suppose that 

 the surface-tension of the liquid con- 

 tained in A is the greater, and that 

 the end of the capillary next A is 

 filled with the pure liquid contained 

 in A, and the end next B with the 

 pure liquid contained in B, while 



between these two points there is a mixture of the two 

 liquids. Then if T x be the surface-tension of the liquid in A, 

 and T 2 that of the liquid in B, the tension along the walls of 

 the capillary will diminish from Tj at the end next A to T 2 at 

 the end next B ; and the skin of liquid forming the surface 

 of contact with the walls of the tube will be urged from B 

 towards A by a force of (T 1 —T 2 )2irr } where r is the radius of 

 the capillary tube. 



* Communicated by Prof. Fitzgerald. 



