544 Dr. R. D- Kleeman on the 



where 



V /o 3 P2 / 



is the change in volume of the liquid and salt. The heat 

 of mixture then is 



C:-( fe t" ,) -s)]( T p-'") + T(tr^-'' 



-f'(fi,)'V»..>-'- 



It should be observed that the latent heat of evaporation 

 L/ of a gnu. of liquid 1 into a vacuum, which was expressed 

 by 



may be obtained in a different form from Clapeyron's equation 



Ll Ll +i % PiJip jJrfP 



where p is the density of the saturated vapour and ;.) its 

 pressure. The value of L/' in the equation may be expressed 

 in the form 



4/3 



v(£) ay/ mi y. 



Another case of mixture of substances which is of interest 

 is a saturated solution of a liquid — say of molecules 1 — in a 

 liquid of molecules 2. To obtain a formula for the heat of 

 mixture in this case, let the piston b in the figure be replaced 

 by one which is solid. Let the pistons c and a be moved in 

 the same way as before till n x grams of molecules 1 have 

 evaporated from the mixture : the corresponding ?? 2 grams 

 of molecules 2 will form with a part of the mixture a saturated 

 solution of molecules 2 in the liquid 1. Let p 3 ' denote the 

 density of this solution, and suppose the ingredients are in 

 the proportion of n/ to n 2 '. If x denotes the number of 

 grams of the mixture which combine with the n 2 grins, of 

 molecules 2. we have 



xn 1 /n l -¥r> 2 n/ 



