ON THE ELECTRICAL PROPERTIES OF PURE SULPHUR. 
71 
purified sulphur, or that there is a constant error in our thermometers, which we have 
no reason to believe. The fact probably is that Brodie did not sufficiently purify 
his crystals from the evil-smelling compounds which they carry with them from the 
bisulphide. 
Monoclinic Sulphur .—The melting-point of perfectly soluble monoclinic sulphur 
was taken by the same observer in connection with a film which had been experi¬ 
mented upon. 
Table III.—Melting-point of Aged Monoclinic Sulphur.* 
Number of experi¬ 
ment. 
Sulphur began to 
melt at 
Melting complete. 
° C. 
°C. 
1 
119-46 
119-96 
2 
120-06 
120-46 
3 
119-06 
119-96 
Mean . 
119-53 
120-13 
This agrees as well as can be expected with the observations of other observers on 
monoclinic sulphur. The fact that the melting-point of monoclinic sulphur, even when 
it has lost its crystallographic properties, is about 120°, may be taken as established 
by these observations. The want of sharpness in melting-point, which is to be 
noticed even in the case of monoclinic sulphur, is marked in all the samples we have 
examined, and is on the whole more pronounced when we deal with mixtures, but not 
markedly so. We think it is established that sulphur, like selenium, has not a 
perfectly sharp melting-point—another point of resemblance between these sub¬ 
stances which we have not seen noticed. Of course, the effect is much more marked 
in the case of selenium than in the case of sulphur; but even with the latter the 
corners of fragments become less sharp and assume a greasy appearance at tempera¬ 
tures a good deal below those at which the fragment is definitely liquid. 
The freezing points of sulphur have not been investigated by us, as they have been 
dealt with most elaborately by Gernez (‘ C.B.,’ loc. cit.). One disadvantage of the 
method of publication adopted in those famous “ Comptes ” is that it effectually 
prevents any estimate being formed of the reliability of experimental work, the 
scarcity of space not allowing sufficient details to be given. 
The melting points of mixtures of monoclinic and electro-positive sulphur are 
* This sulphur was afterwards found by Professor David to have lost its crystallo-optic properties, 
and could not be distinguished by the polariscope from octahedral sulphur. We have ventured to call 
this variety “aged monoclinic” sulphur. It is probably generally formed as a preliminary step in the 
formation of octahedral sulphur from monoclinic at ordinary temperatures. 
