2 
Proceedings of the Koyal Society of Edinburgh. [Sess. 
bottom of the tube with a glass rod immersed in the sulphur. Crystals of 
S n i, of S l5 and of S n appear in succession, the whole mass changing into 
S n before final solidification. 
The freezing-points with pure liquid S A may be called the ideal freezing- 
points ; those with S A and S M in equilibrium are called the natural freezing- 
points. 
Freezing-Points of S m . — By melting pure sulphur at 123°, placing it 
in a bath at 102°, and using a thermometer instead of the glass rod, 
the temperature at which S m crystallises from almost pure S A may be 
obtained. The ideal freezing-point, S\->S III5 is 106*8°. After half a minute 
the crystallisation of S n begins, and the temperature rises. 
The natural freezing-point of S m is observed by treating the melted 
sulphur with ammonia gas at 130-140°, to facilitate the formation of S M , 
and then immersing the tube in a bath at 99°. The freezing-point 
S M ^S A ->S m is 103*4°, the depression being due to 3*1 per cent of S M which 
is in equilibrium with the S A at that temperature. After remaining at 
this point for a short time, crystals of S : appear, with rising temperature, 
and finally S„ comes out with a still further rise in temperature. 
Freezing-Points of S v — The sulphur is treated in the same ways as 
before, but the bath is kept at 108° (above the freezing-point of S m ). 
With pure S A the freezing-point S A ->S* is 112*8°; with the mixture of 
S A and S M in equilibrium (3*4 per cent, of the latter) the freezing-point 
is 110*2°. After an interval S n comes out, and the tempera- 
ture rises as usual. 
Freezing-Points of Various Forms of Sulphur. 
Solid 
Phase. 
Point in Diagram. 
Freezing- 
Point. 
Per cent. 
S*. 
Sn 
A, Ideal f.-p., S A ->S n 
119*25 
o-o 
B, Nat. f.-p., S^^Sx-^Sn 
114*5 
3-6 
Si 
C, Ideal f.-p., S A ->Si 
112-8 
minute 
D, Nat. f.-p., S^^Sa-^Si 
110-2 
3-4 
Sm 
E, Ideal f.-p., S A — >Sm 
106-8 
minute 
F, Nat. f.-p., S M S A -> S m 
103-4 
3-1 
Of these data, the first was determined by Smith and Holmes,* the second 
by Smith and Carson,*]* and the others in the present work. 
It will be seen that the widely quoted values for the “ melting-points ” 
of the various forms of sulphur — S D 114*5° (Brodie); S n , 120° (Brodie); 
* Proceedings , xxiv. 299. t Ibid., xxvi. 352. 
