588 Proceedings of Royal Society of Edinburgh. [skss. 
On Two Liquid States of Sulphur S A and S M and their 
Transition Point. By Alexander Smith. 
(MS. received February 17, 1905. Read March 20, 1905.) 
(Abstract.) 
It is well known that melted sulphur when heated becomes 
suddenly dark brown and viscous in the neighbourhood of 160- 
170°. These and other facts rendered it probable that there was 
a transition point in liquid sulphur, and that two liquid states 
could be proved to exist, one of them being stable below the 
transition point, and the other above it. According to the phase 
rule, a single substance can exist in three phases (two liquid and 
one vapour phase) only as a non-variant system at a single tempera- 
ture and pressure. Thus, if the two liquid forms were not 
completely miscible, the lower one might form the greater part of 
the material until, as the temperature rose, it became saturated 
with the upper one and a new phase separated out. This 
phenomenon would mark the transition point, and the smallest 
further rise in temperature would cause the complete disappearance 
of the first phase. The substance would then contain a small 
proportion of the lower form in solution in the upper, and this 
proportion would diminish with rising temperature. No case of 
an exactly parallel nature is known ; but the transition from 
“liquid crystals” to an isotropic liquid in the case of certain 
organic compounds is to a certain extent analogous. 
For the discovery of a transition point of this kind the study of 
the progressive change in any physical property as the temperature 
rises is available. The author examined successively the change 
in viscosity, the change in solubility, the variation in the co- 
efficient of dilatation, and the rather marked absorption of heat 
which is observed to accompany the sudden onset of viscosity in 
the fluid. The results were as follows : — 
1 . In melted sulphur, easily perceptible viscosity appears first at 
159*5°. At 160° the viscosity is already very great. 
2. When sulphur is held at 162*5° or any higher temperature a 
sudden absorption of heat and simultaneous sudden access of vis- 
cosity occur, and the temperature falls to 162°. The transition 
point is therefore not above the latter temperature. 
3. Distilled sulphur does not show either of these phenomena 
