284 I Dandeno : Osmotic theories 



have nothing to do with the subject, for* ** The law of osmotic 

 pressure holds for all substances no matter what the nature." 

 However, we have to know something of the meaning of these 

 terms before we can interpret the statements and definitions given 

 in the text-books on physics. The following statement f gives a 

 common idea with regard to osmosis : "When liquids or gases 

 force their way through porous septa and mix the diffusion is 

 called osmose." Now this would actually not be osmosis at all 

 unless the septum is porous only to such an extent as will permit, 

 yet hinder to some extent, the passage of the liquid. According 

 to the definition given above, the process Is diffusion merely. But 

 since the term '' force their way through/' is used, we have to 

 conclude that it is not mere diffusion. The definition includes, 

 therefore, something of a contradiction. In the following quota- 

 tion is given another view of the osmotic action : J "In case of 

 two liquids separated by a porous septum, the liquid which wets 

 the septum the better, passes through the more rapidly." This is 

 intended to imply that the attraction which the septum has for the 

 liquid is the factor including osmose, but this is not true in many 

 cases, as for example in the case of the pig's bladder and thistle- 

 tube experiment. For example, when a little caustic potash has 

 been added to the sugar solution which Is placed on one side of 

 the septum, and pure water on the other, the sugar solution, aided 

 by the alkali, wets the membrane more quickly than pure water, 

 yet the water passes through the membrane more readily, and the 

 movement is inward. In fact, the sugar solution does not pass 

 through at all, at least not for a considerable time. Referring to 

 the subject of osmosis, Anthony & Brackett§ say '* An explana- 

 tion of these facts follows if we suppose that diffusion of a liquid 

 through a continuous membrane can occur only when the liquid 

 is capable of temporarily uniting with the membrane and forming 



r 



part of it/' From this it appears that the membrane itself is the 

 active agent in the process, and that osmotic pressure is due to 

 the attraction and perhaps chemical action of the membrane. 



Enough has been said about the general view of osmotic ac- 



*Ostwald, Outlines of general chemistry, 128. 1S95. 

 -[•Gage & Fessenden, Text-book on physics, 43. 18S7. 

 J AppTeton, Chemical philosophy, 132, 1897 [ed. 4]. 

 I Text-book of physics, 106. 1888 [ed. 4]. 



