( 691 ) 
(é)o + T Bae van = (Ev + lp zb | var» 
We may prove, — in the same way as we have done for a binary 
mixture (Cont. IT, pag. 110) — that this quantity represents also 
for a ternary mixture and even for a mixture with an arbitrary 
number of components, the heat given out per molecule of the second 
phasis in the above mentioned process. We represent this quantity 
by the sign Wa); so we put 
op 
m Way = m (En) + (Gr) Var + PMU) 
This formula is simply an application of the principal formula of 
thermodynamics : 
dQ = de + pdv. 
For the application of equation (I) knowledge of the signs of va; 
and Ws, is required in the first place. 
The rule for the sign of vg, is very simple. If the first phasis is 
represented by a point on the liquid sheet of the coexistence surface, 
then vg; is positive. If on the other hand that point is to be found 
on the vapour sheet, v2, is negative; and, as we saw already on 
pag. 686, var = 0 if the first phasis is represented by a point on the 
contour of the coexistence surface, so on the limit between vapour 
and liquid sheet. (See for a binary system Cont. II, pag. 126). 
In this the transition of the sign of vs, from positive to negative 
takes place. It is true that the value of vs, is also zero in the 
plaitpoint, but there the value zero is not a transition from positive 
to negative; at both sides of the plaitpoint vs, has the same sign; 
positive if the plaitpoint lies on the liquid sheet and vice versa. In - 
the plaitpoint vj, may be written: 
abs aT 2 (eo — #y) (yg — 91) (— = Piles wt (@), | 
. at very litle distance from the plaitpoint the value of vg, will 
not perceptibly differ from this value. At the end of our previous 
chapter we have discussed the sign of this expression. 
If we put 
5 ro =)? 
dw 
va ene aa (2 — ran ran lta Mik = = 
vj — Sr 
dv,? 
and if we represent an element of the right line, connecting the 
first phasis with the second, by d/, then we get (pag. 686) 
