( 450 ) 
the second part of the Con- 
tinuity and which is here 
reproduced. Between two 
values of p, viz. the maxi- 
mum pressure and the mini- 
mum pressure of the iso- 
thermal, ¢ is trivalent 
and the transition of the 
vapour sheet to the liquid 
sheet takes place through 
a curve which has two 
cusps. For the rest the fact 
that the ¢-surface thought 
as function of # and y con- 
Fig. 1. sists of three sheets in some 
| cases and of one sheet in 
other cases and that £ in the neighbourhood of the eritical circum- 
stances for the same value of p and 7, will have three values above 
one part of the values of z and y, and will have one value above 
the remaining values of # and y, shows that the metastable and 
unstable part of the ¢-surface will show a more intricate configuration 
than what we call a plait. 
Let us begin with examining for a simple substance the value 
of £ for a molecular quantity as function of p, assuming the tempe- 
rature to be constant. From the differential equation do = vdp we 
could derive £, if we could give v as function of p. For the rarefied 
MRT ; 
gaseous state we may put v= ——,, from which follows: 
P 
t= f(T) + MRT log p. 
[ow == py |p dv, 
C= MRT — MET logv, 
If we write 
we get 
or 
aw 4 
By combining these equations we get f(7) = MRT — MRT log MRI. 
The vapour branch of the ¢-curve appears therefore to rise with 
