RECENT EXPERIMENTAL WORK ON 

 OSMOTIC PRESSURE 



By JAMES C. PHILIP, M.A., Ph.D., D.Sc. 

 Lecturer on Physical Chemistry, Royal College of Science, London 



The number of scientific workers who have made an experimental 

 study of the phenomena of osmotic pressure is not great. The 

 phenomena themselves are of fascinating interest and of 

 fundamental importance, especially on their quantitative side, 

 and the paucity of available data must be attributed to the 

 experimental difficulties which arise when an accurate measure- 

 ment of osmotic pressure is attempted. Among these difficulties 

 must be reckoned the unreliable character of the rigid media 

 which have been employed for the support of the all-important 

 semi-permeable membrane. Pots or tubes of unglazed por- 

 celain are commonly used for this purpose, but out of a given 

 consignment of pots or tubes, presumably more or less uniform, 

 only one or two probably will permit the deposition of an 

 absolutely satisfactory membrane. The reasons for the pos- 

 sibility or impossibility of depositing a satisfactory membrane 

 on a given pot or tube seem to be imperfectly understood, but 

 of the facts there is little doubt. Examples of this difficulty may 

 be found even in the most recent work on osmotic pressure. 

 Thus Messrs. Morse and Frazer 1 found that of a lot of five hundred 

 pots made for them, not one was suitable for the measurement 

 of osmotic pressure, while in the case of another lot of one 

 hundred pots some twenty-five or thirty were fairly satisfactory. 

 Again, the Earl of Berkeley and Mr. Hartley, 2 who use porcelain 

 tubes in their experiments on the osmotic pressure of concen- 

 trated solutions, state that of one hundred tubes of various makes 

 only three permitted the deposition of a really efficient membrane. 

 Morse and Frazer, it is true, indicate that they have some 

 evidence as to the conditions essential for a useful porous wall, 



' American Chemical Journal, 1905, 34, 1. 

 2 Philosophical Transactions, 1906, A, 206, 481. 



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