28G Dandeno : Osmotic theories 



cell which sustained a pressure of 31 atmospheres, certainly an 

 enormous pressure. Until the electrical method of arranging the 

 cell was developed, a pressure of no such magnitude had ever been 

 obtained. 



Recently there has been prepared a good work on osmotic 

 action and its bearing upon plants, by B. E. Livingston."^ While 

 this work covers the ground rather thoroughly, it does not refer 

 to Morse's work, and it holds too strictly to van't Hoff*s theory 

 of osmotic pressure. However, Livingston's book is by far the 

 most comprehensive and readable on the subject in the English 

 language to-day. 



With rerrard to 



/ 



M 



rathe 



Pfeffer as the originator of the Pfeffer cell, Morse for the develop- 

 ment of the cell for high pressure, van't Hoff for an expression of 

 a theory of osmotic pressure, comparing the solute to a gas, and 

 de Vries for recorded results of relative osmotic pressures in plants- 

 It is mainly in regard to osmotic presstire ^r\d the theories advanced 

 to explain It, that the present discussion is offered. The theory 

 of van't Hoff is the one most generally accepted at the present 

 time, and the only other one that has been offered is now^ con- 

 old and insufficient The chief objections to both 

 theories are that they do not explain^ and that, in several cases, 

 they leave much to be desired in regard to several phases of 

 osmotic phenomena. Van't Hoff*s theory, when put into simple 

 English, is as follows: ''Dissolved substances exert the same 

 pressure in the form of osmotic pressure as they would exert were 

 they gasified, at the same temperature, without change of volume," 

 and this idea has been widely accepted. The main reason for its 

 general acceptance is that it seems to harmonize with certain other 

 well-known physical laws ; but van't Hoff himself does not appear 

 to have had any experimental knowledge of the actual pressure 

 which osmotic substances do exert. His law, as well as Ostwald's 

 conclusions with regard to the magnitude of osmotic pressure, w-as 

 based on Pfeffer's researches, and Pfeffer himself was not able to 

 measure osmotic pressure when such pressure reached a point as 

 high as five or six atmospheres. Pfeffer's work in this regard has 



* Livingston, •« The r5!e of diffusion and osmotic pressure in plants." 1903- 



