377 
value of W,,, will continually decrease, and that of W, will in- 
crease. From this it follows that the numerator which is at first 
negative, will likewise pass through zero and become positive. This 
happens before the second quadruple point g has been reached, for 
in that point the numerator must be positive already. So we arrive 
7 
d 
at the conclusion that 7 = for the three-phase line S, + S, + G 
starting from b is negative, then passes through zero, and has a 
positive value in g, so that the said three-phase line, which joins 
the two quadruple points 5 and g, possesses a minimum pressure, 
as is indicated in fig. 3. 
The considerations given here may be directly applied to the 
fourth three-phase line of the mentioned two quadruple points, viz. 
to that for S, + S,-+ L. The equation, which we want in this case, 
is quite analogous with equation (1), and we need only substitute 
the letter / for g to obtain the true relation, so: 
: Vl WEE WEL 
dp Aen, Kf mn 4 
gp -- ne ee en 
dT Jas a Bs, —®I 
Sie as Vol 
Us, — Ul 
The discussion of the numerator is perfectly identical with that 
just given, but now the denominator requires further consideration. 
We were convinced that Vg, and Vs, are negative, but about 
the quantities Vs, and Vs, we must make the following remarks. 
The known increase of volume, which takes place in iron-carbon 
mixtures on solidification leads us to expect that this property is to 
be attributed to the presence of the component carbon, which behaves 
probably in the same way as the substance water. In consequence 
of this not only carbon, but also carbon-compounds will exhibit in- 
erease of volume on solidification, specially when the compound 
25 
Proceedings Royal Acad. Amsterdam. Vol. XV. 
