1216 
2 dP oe. 
From the value of aie from (8) it follows that this is not equal to 
5 À : 5 ; a ee 
oe the P.7-curve corresponding with the straight line X/Y of 
fig. 1 (IV) will, therefore, not meet, in fig. 4(IV), the melting point 
line Hd in F. Whereas, as we have stated previously, all the P,7- 
curves in fig. (IV) meet the melting point line of /” in the point / 
this is no longer the case when the straight line ZZ, in fig. 1 (LV) 
coincides with NX/'Y. 
In order to determine this P,7-curve in the vicinity of F more 
closely we eliminate da” from (6) and (7); we then get: 
a, de* +-...—=(A4Q—CS) dP— (BQ—DS) d!I'+b, dedP+c,dadT+... . . (10) 
In this equation, as dP and dT are according to (9) of the order 
dz?, dedP, and dedT are of the order dz*; the terms omitted are 
all of the order dx* and higher. We now substitute in (10) the 
value of de which we can deduce from (7) namely: 
dekt AE Eee ime ae (11) 
so that (10) is converted into 
de (AdP— BdT)'l2 = (AQ— CS) dP — (BQ—DS) dT + 
4 a, (Adp—BaT)'h(b,dP He, dT) . . .- (12) 
in which the terms omitted are of an order higher than dz*. For 
(12) we write: ; 
(AQ—CS) dP --(BQ—DS) dT = (b, dP He, dT)(AdP--BdT)y'2 . (13) 
or: ij 
(a, Y—b, X) =(b, ¥ He, XP(AY—BX). … RO 
In order to investigate (14) we take a straight line a, Y—h, X=d, 
in which d is infinitely small so that this line is situated parallel to, 
and in the immediate vicinity of, the tangent in the point /” Its 
points of intersection with (14) are given by: 
a, Y —b, X= @ and (ble, A (AY BX) dE 
This is satisfied by ; 
Pe lande (15) 
hence -a,a, —~ 0,6, — 0: and: (6,0; + €,b,) (Aa, — Bb) =d 
OE: 
bs 2 ’ 
73 (Ab, — Ba,) (6,6, Hea) = le . . «= (16) 
4 
3 
5 (AB, Ba jbbs 4 oa) vos 32 
4 
As X and Y do not change their sign when dg does so, it follows 
