on Osmotic Tlieory. 265 



z and f are the specific volumes of the solution and mixed 

 vapours respectively. 



s & and <7 a are the apparent spec, vols.* of component A in 

 the solution and mixed vapours respectively. 



s b and a-* are the apparent spec. vols, of component B in 

 the solution and mixed vapours respectively. 



a and a are the number of grammes of A per gramme of 

 solution and mixed vapours respectively. 



b and /3 f are the number of grammes of: B per gramme of 

 solution and mixed vapours respectively. 



Note that a+6 = a + j3 = l. 



For the pure Components^ Liquid or Vapour. 

 p & and 7r a are the pressures on the pure liquid A and on the 



pure vapour of A respectively. 

 p b and ir b are the pressures on the pure liquid B and on the 



pure vapour of B respectively. 

 z & and f a are the specific volumes of pure liquid A and pure 



vapour respectively. 

 z h and f 6 are the specific volumes of pure liquid B and pure 



vapour respectively. 



When it is necessary to specify that the quantities are 

 those belonging to vapour in equilibrium with a liquid under 

 a particular pressure, that pressure will, following Porter's 

 notation (Proc. P. S., A. vol. lxxix. 1907, p. 519), be denoted 

 by adding it as a suffix. Thus : 



tjr p is the pressure on the mixed vapours when they are in 



equilibrium with the solution under pressure p. 

 7r a is the pressure on the pure vapour of component A 

 when it is in equilibrium with the solution (o£ con- 

 centration a) under pressure p ; and with the mixed 

 vapours (of concentration a) when the pressure on 

 them is ijr . 



* The term " apparent specific volume " is used for brevity's sake ;■ 

 the quantities referred to represent the change in volume of a large mass 

 of solution (or mixed vapours) when one gramme of the component under 

 discussion escapes from it under (osmotic) equilibrium conditions. That 

 is to say, we assume that the mass of the solution is so large that, after 

 this operation, there is no first- order change either in the osmotic 

 pressure or in the concentration. The relation between the true and 

 apparent specific volumes of any component in a solution is discussed in 

 a communication to the Royal Society, entitled " Osmotic Pressures 

 derived from Vapour-pressure Measurements." 



t It is to be noted that the concentration of the components in the 

 mixed vapour is by no means always the same as in the liquid mixture. 



