PAPERS OX CHEMISTRY AND PHYSICS 253 



Second, tlie method has not been applied to polar sol- 

 vents. Third, in any case, the solubility must have been 

 determined in a series of selected solvents before the 

 solubility in other solvents may be calculated. 



In the pages which follow we have described a method 

 of calculating solubilities which requires but a minimum 

 of physical measurements and which will apply to polar 

 as well as to non-polar solvents providing there are no 

 molecular compounds or solid solutions produced. It 

 should be possible also to tell which systems will give 

 partially miscible and which immiscible liquid systems. 



DEVELOPMENT OF METHOD 



From equation (1) it is evident that the slope of the 

 log N vs. 1/T curves is related to the latent heat of fu- 

 sion of the solute in the following manner, 

 A log N — L 



Slope = S = = (2) 



A, tlT) 4.58 



Equation (2) applies only to those binary mixtures in 

 which the heat effect of the solution process is equal to 

 the latent heat of fusion of the solute. Now it is a gen- 

 eral rule, providing no secondary molecular effects are 

 produced, that the negative heat effect accompanying 

 the solution process is greater than the latent heat of 

 fusion. In all such cases the slope of the logarithmic 

 curves must be greater than that of the ideal slope. This 

 is well sho^vn in Table 1. 



The ideal slope for any solute is that slope which 

 would be obtained with a solvent which gives a thermo- 

 dynamically ideal mixture. It is evident from Equation 

 (2) that the value of the ideal slope may be calculated by 

 dividing the latent heat of fusion of the solute (in small 

 calories per mole) by the constant 4.58. 



If now the experimental values of the slopes of the 

 log X vs 1/T curves for a given solute in a variety of 

 solvents be divided by the value of the ideal slope for 

 that solute, there is obtained a series of factors the mag- 

 nitude of which is a measure of the non-ideality of the 

 mixture. 



In Table 1 are given values of the slopes and of the 

 factors which have been calculated for the four solutes, 



