On an Experimental Modification of van cler Waals's Equation. 133 
If C, represents the specific heat of the saturated vapour we may write 
C. = C„ + T^g (2.) 
while C„ is connected with by the relation — 
C, = a^>T ^y^dv (23) 
We may also write — 
loo 
C..=;7^1 (21) 
Combining these results we find for the specific heat of the saturated 
vapour in terms of reduced magnitudes — 
a - -^2 
Along the inversion curve C, vanishes ; its equation is therefore given l)y — 
7-^=1 p-^ . . (^6) 
From equation (9) we find- 
8 , 3 1-5 
and- 
P^cho^- -£i-^ (28) 
so that the inversion curve becomes — 
y =1 1 • • (29) 
8co d.^ \3u)-l 8(0^' 
The right-hand member of the equation was evaluated from the constants 
of Table XL, and the following results were thus obtained : — 
