436 Earl of Berkeley and Mr. E. G. J. Hartley. [Apr. 21, 



found that no emergent column correction could be satisfactorily 

 applied ; the pressures, however, under which the saturated solutions 

 boiled were recorded. 



The results are given in a tabular form at the end of the paper. 



" A Method of Measuring directly High Osmotic Pressures." By 

 the Earl of Berkeley and E. G-. J. Hartley. Communicated 

 by W. C. D. Whetham, F.R.S. Beceived April 21 —Read 

 June 2, 1904. 



This paper gives an account of some preliminary experiments made 

 in furtherance of a scheme of work outlined by one of us in a 

 communication to the Royal Society.* 



The ordinary method of determining osmotic pressures, i.e., that 

 adopted by Pfeffer,f Adie,J and others, is evidently not suitable for 

 high pressures ; the difficulty of attaching the manometer to the 

 porous pot in a manner such that it will not move at the junction is 

 practically unsurmountable. 



It seemed likely that if a porous plate were tightly squeezed between 

 two hollow hemispheres, the necessary conditions of stability might 

 be attained, and the first apparatus carried out this idea. It was 

 made by Messrs. Midler in 1901, and, being of glass, was designed 

 only to stand moderate pressures, though it was hoped that, in a way 

 described below, it might be used to measure indirectly the osmotic 

 pressures of concentrated solutions. It consisted of two glass globes 

 A and B (see fig. 1), holding the porous plate C between them. The 

 plate was glazed round the edge, and carried the semi-permeable 

 membrane of copper ferrocyanide on the face adjacent to the solution. 

 A rubber ring on either side of C and between it and the glass flanges 

 of A and B, served to form a watertight joint when A, B and C were 

 strongly pressed together by means of a suitable brass fitting, which, 

 however, is not shown in the figure. 



It had been intended to put solutions of different concentrations in 

 the two vessels, and measure the difference between their osmotic 

 pressures ; it was found that, although it would be possible to obtain 

 the desired result, yet the time taken for the pressure to develop was 

 too long. 



An experiment with a solution of 114-7 grammes of sugar in the 



* Earl of Berkeley, " Experimental Determinations for Saturated Solutions," 

 read May 19, 1904, see p. 435. 



+ W. Pfeffer, ' Osmotische Untersucaungen,' Leipsic, 1877. 

 E. H. Adie, ' Jl. Chem. Soc.,' 1891, p. 344. 



