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VJII. On the Osmotic Pressures of Aqueous Solutions of Calcium Ferrocyanide. 



Part I. Concentrated Solutions. 



By the EARL OF BERKELEY, F.R.S., E. G. J. HARTLEY, B.A. (Oxon.), 

 and C. V. BURTON, D.Sc. (Land.). 



Received July 4, Read November 5, 1908. 



IN the following communication the experiments on the direct measurement of the 

 osmotic pressures, on the vapour pressures, and on the densities have been carried 

 out in conjunction with Mr. E. G. J. HARTLEY, those on the compressibilities with 

 Dr. C. V. BURTON. 



In the 'Proceedings of the Royal Society,' Series A, vol. 77 (1906), pp. 15G-1G9, 

 Mr. HARTLEY and I gave a preliminary account of the determination of the osmotic 

 pressures of strong aqueous solutions of cane sugar by means of measurements of the 

 relative lowering of their vapour pressures as compared to that of water. We deduced 

 a formula for the connection between the vapour and osmotic pressures of a solution, 

 which, in view of the experimental errors, justified the neglect of corrections due to 

 the compression of the solution and of the solvent. Since then Prof. A. W. PORTER 

 (' Proc. Roy. Soc.,' A, vol. 79, 1907) has put forward an exact equation in which the 

 influence of these two factors can be taken into account ; increased experience with, 

 and further modifications of, the vapour-pressure apparatus apparently justified the 

 belief that the experiments would be more accurate, and therefore it seemed advisable 

 to endeavour to obtain complete data for the aqueous solutions of some one substance, 

 so as to test the practical applicability of the new formula in its entirety. 



The equation in question is 



rp r^oo rp PP 



sdp= Ydp+\ udp (1) 



Jw w > Jiroo 



and the notation is as follows : 



For the Solution : 



The hydrostatic pressure on the solution is p. 



The vapour pressure when the solution is in contact with its own vapour 



alone "V- 



Reduction of volume when 1 gramme of solvent escapes at pressure p . . s p . 



Osmotic equilibrium pressure for a hydrostatic pressure p Pp. 



VOL. CCIX. A 448. 2 A 28.11.08 



