354 Proceedings of Royal Society of Edinburgh. [sess. 
B is the freezing point of S^, and its exact location is unknown, 
and G is the eutectic point (also unknown.) 
The curve DG in the diagram is the line showing the pro- 
portions of Sa. and in the liquid at various temperatures, and 
extends from the natural freezing-point to the boiling-point. Only 
the lower part is shown. The general form of this curve was 
determined by measurements at intervals of ten degrees, which were 
given in a previous paper (these Proceedings, vol. xxv. (1905), 
p. 590, par. 2). The proof that there were two distinct forms of 
liquid sulphur, given in another paper (these Proceedings, vol. xxv. 
(1905), p. 588), however, suggested the possibility that there might 
be a transition point at which a sudden change from little to much 
took place, with formation of a new phase composed mainly of 
viscous sulphur. The dilatometric experiments given in the last- 
mentioned paper showed that this point, if it existed, must be 
situated at 160’0°, the point of minimum coefficient of dilatation. 
In order to ascertain whether any such sudden increase in the 
proportion of occurs, a new series of observations in the 
neighbourhood of 160° has now been made, and the exact form of 
the curve in this region has been determined. These measure- 
ments show that, when equilibrium has been reached, the pro- 
portion of at 155° is 7 ‘7 per cent, and at 165° 15 ’5 per cent., and 
that the change in concentration, degree by degree, between these 
points is continuous. It follows, therefore, that although there 
are two markedly different forms of liquid sulphur, these forms 
are miscible in one another to such an extent that no separation 
into phases occurs when the system is in equilibrium. At all 
events, the new observations do not afford any evidence that there 
is a separation. The two phases can be observed only when the 
system is cooling and is in an unstable condition. 
In view of the conclusion just mentioned, there was at least one 
anomaly which required explanation, namely, the marked absorption 
of heat and fall in temperature at, or just above, 160°, which are 
observed when liquid sulphur is heated continuously. The 
phenomenon is so strongly suggestive of a transition point, 
accompanied by the formation of k new phase, that it requires 
separate elucidation. A large number of experiments, of which a 
few illustrations only are here given, served to clear up the difficulty. 
