In the above case of dissociation the formula would be
For a coexistent solid phase of the solvent we have for constant pressure
being for convenience taken the same in both phases.
Then
In integrating for small values of we may treat the coefficients of and as constant. This gives
or if we write for (the latent heat of melting for the unit of weight of the solvent), we have
This may be written
According to Raoult, the first member of this equation has a value nearly identical for all solvents and solutes (supposed definite compounds). This would make the second member the same for all liquids of "definite" composition, when we give the value for the molecule in the liquid state. I should think it more likely that these properties should hold for the two members of the equation
which are pure numbers (of no dimensions in physical units). In this form it has a certain analogy with van der Waals' law of "corresponding states."
With a coexistent vapor phase of the solvent, we have