1900] on Osmotic Phenomena. 495 



more complete study of the vapour-pressures of strong solutions may 

 be expected to throw additional light on the subject. , 



The essential point of the theory here sketched is that the 

 equilibrium existing in a solution is one between definite chemical 

 compounds and the solvent, giving rise to a simple vapour-pressure 

 relation by means of which the phenomena may be studied and 

 elucidated. There is a great deal of work to be done before such a 

 theory can be regarded as established, but in the mean time it may 

 serve very well as a working hypothesis for correlating experimental 

 results, and suggesting new lines of investigation. Eegarded in this 

 light, the vapour-pressure theory may serve a useful purpose, and 

 judging by the experimental data at present available, I think I may 

 fairly claim to have made out a good prinid-facie case for the theory. 



[H. L. C] 



Note.— The vapour-current-indicator is a development of the old 

 smoke-jack. A light spiral vane with a mirror attached is suspended 

 in a tube which nearly fits it by means of a quartz fibre. Joule 

 (Proc. Phil. Soc, Manchester, vii. 35) employed a wire spiral sus- 

 pended by a silk fibre for indicating air currents, but does not seem 

 to have adapted it for purposes of exact measurement. The instru- 

 ment shown in the lecture gave a deflection of oO° (500 mm. at 

 1 metre) for a velocity of air current '01 cm. /sec. The sensitiveness 

 might easily have been increased, but the above amply suffices for 

 most purposes. 



