191% 
that the P,7-curve has in point a cusp so that we find at both 
sides of the tangent in /’ a branch of this curve. Now a,= A(Q—aS 
a B (Q A. wS) 
Ab, — Ba, =(BC — AD) S 
so that Ab,— Ba, is positive. From (16) and (17) it now follows 
that 6, and A(Q— 2S) have the same sign, and the same applies 
to a, and B(Q—uS). 
In connection with (15) follows: 
dT of X has the same sign as A(Q—AS) .-. (48) 
DEED ARE ne (OENE ENEN 
what agrees with (9). 
We will now consider some cases. 
Po henes A Wand Aes tr ASO Gelk 
From 
dm Ar On A r Fs | (20) 
SER Bres Q—i5 
d B 
it follows that oe is smaller than a (From our assumption 
BC—AD>0 follows namely 2 — u >0). If in fig. 1 the line d,Fd 
represents the tangent at the point / of the not drawn melting point 
line, the P,7-curve NFV will, in its turning point /’, have a tangent 
like the dotted line in fig. 1 passing through /. From (18) and (19) 
and also from (9) it follows that dP and dT are negative, so that the 
curve Y/’)’ in fig. 1 must proceed from / towards lower temperatures 
and pressures. The latter may be 
found also by other means. For 
this we take the minimum 
melting point of the compound 
I’, therefore the temperature 
Tr of fig. 1; as Q —AS <0, 
the saturation line of / under 
its own vapour pressure has at 
this temperature a form like 
T curve afb in fig. 1 (ID) in which 
Fig. I. we must also imagine the tangent 
XI Y to be drawn. As this tangent has only one point in common 
with the saturation curve, namely the point of contact /, a vertical 
line passing in fig. 1 through the point /” may intersect the curve 
XF Yin the point /’ only. 
We now take a temperature 7’ somewhat lower than 7'p; if 
(oF 
