At the triple point,
Latent heat of sublimation = Latent heat of vaporization = Latent heat of fusion

Example 2.2
The vapour pressure of mercury at 399 K & 401 K is found 0.988 and 1.084 mm of mercury respectively. Calculate the latent heat of vaporization of liquid at 400 K.

Solution:
Let P₁ = vapourtor of mercury = 0.988mm at T₁
P₂ = vapourtor of mercury = 1.084mm at T₂

Now,
Again
Applying clausius, clayperon equation for vaporization

Or