264 The Earl of Berkeley : Notes 



yjr, is the pressure on the mixed vapours when they are in 



equilibrium (through a membrane) with the solution 

 under the same pressure *. 



7r a7r is the pressure o£ the pure vapour of component A 

 when it is in equilibrium (through a membrane) with 

 the pure liquid A under the same pressure *. 



i/r and 7r a0 will be reserved to denote the values of -yjr . and 

 7r a7r when no membranes are present. 



7r a is the partial pressure of component A in the mixed 

 vapours. 



7Tg is the partial pressure of component B in the mixed 

 vapours. 



The Osmotic Pressures. 



P a and P A are those of the solution when the membrane is 

 permeable to liquid A or B respectively. They will 

 be referred io as complementary osmotic pressures. 

 Y*=P-P* and F b =p-p b . 

 H a and IL are those of the mixed vapours (measured 

 against a pure vapour) when the membrane is 

 permeable to the vapour of A or B respectively. 

 II a = ^-7r a and H^yjr-Wy 



[r> is that of the solution when the membrane is perme- 

 able to the vapours of both A and B. 



IP and lF fl are those of the solution in contact with the 

 mixed vapours when the membrane is permeable 

 only to the vapour of A or B respectively. 



a/3 a J8 F T p' 



That these three osmotic pressures are equal will be seen 

 later. In practice it is convenient to distinguish between 

 them. 



IP and IP, are those of the solution in contact with the 



a o 



pure vapours when the membrane is permeable to 

 the vapour of A or B respectively. 



K-P- : K and [p 6=P- 7r 6- 



* It is to be remarked that neither^ nor 7r a7T is uniquely defined, 

 for, with a membrane present, it is possible to have a series of values of 

 (say) 7r a which will satisfy the definition. 



