( 538 ) 
as to the three-phase equilibria in the system p-dichlorobenzene — 
p-dibromobenzene, the same system of which, thanks to Foster 
and Speranski (l.c.), we already know a series of solid-gas equilibria. 
Fig. 1 is a combined PT and ^-projection: 0 A and Ob are the 
triple points of the components. They are connected by the three- 
phase line. In the Tx projection this line divides into three branches 
which indicate, respectively, the composition of the solid [S) liquid 
(L) and gas (6r) phases. 
Since the influence of the pressure on the equilibrium LS, is 
very trifling and as triple-point pressures are comparatively low, 
the branches S and L may, usually, be taken as being equal 
respectively to the melting-point curve and the freezing-point curve*) 
at 1 atmosphere. 
In fig. 1 is assumed Po A > Po B l ) which case we will call chief 
type I. We will now ascertain under what conditions three con¬ 
ceivable cases might occur, namely: 
case a with a maximum pressure in the three-phase line 
„ b „ „ minimum „ „ „ „ „ 
„ c without a max. or min. „ „ „ „ 
To get an insight as to the change of the pressure with the tem- 
x ) A (as is customary) is the name of the component with the lowest melting 
point and with a vapour pressure greater than that of B at the same temperature. 
2 ) In what follows we shall speak of these curves “as the branches of the 
melting diagram.” 
