ON THE ELECTRICAL PROPERTIES OE PURE SULPHUR. 
69 
remelted in vacuo before being used—but this we only began to do in 1893, after the 
above facts were discovered. We should like to hazard the mere guess that the gas 
is water vapour, and that it is taken up during the formation of the sulphur snow, 
which is always present when sulphur vapour condenses in a retort and receiver. 
General Physical Properties of Purified Sulphur. 
We have not any very serious corrections to make to the observations of previous 
workers—in other words, very pure sulphur does not differ appreciably in ordinary 
characteristics from sulphur which is only moderately pure. The most obvious physical 
datum of a fusible solid is the melting-point, and this is, in the case of sulphur, still 
rather a matter of uncertainty. The most important contribution to our knowledge 
of this constant was supplied by B. C. Brodie (‘Proc. Boy. Soc.,’ vol. 7, p. 24) in the 
year 1854. The main results, as far as melting-point is concerned, are as follows 
1. Pure (?) octahedral sulphur crystallized from carbon bisulphide melts at 
114°-5 C. 
2. But octahedral sulphur begins to change into monoclinic sulphur below this 
temperature ; and 
3. The melting-point of pure monoclinic sulphur is 120° G. 
4. Mixtures of octahedral and monoclinic sulphur melt at temperatures between 
114°'5 and 120° C. 
No data are given as to how the sulphur was purified, nor as to the method adopted 
for finding the melting-point. We will add to this statement the following account, 
which may be regarded as summarising a large number of experiments. 
Method. —We have always employed the method of heating small particles in 
thin glass tubes alongside a thermometer. We are aware (though we cannot find the 
reference) that a recent observer who carefully examined the relative accuracy of 
different methods, decided that the best method to employ in determining melting- 
points is that of using a large quantity of the substance and plotting a cooling curve. 
In the case of sulphur, however, this method is rather difficult for many reasons— 
some of which will be evident on referring to Brodie’s paper—and with any method 
the very small conductivity of sulphur constitutes a grave difficulty. 
Our thermometers, which we had hoped to have standardized at Kew, were, by an 
oversight, only standardized up to 100° C., and to send them to Kew for the over¬ 
sight to be remedied would have required too much time. They were, however, very 
good. One was six years old at least, and its B.P. was too high by 1°'34 C. We 
have confidence that the observations are correct, as far as the thermometers go, within 
about T° C., within which limit the thermometers were in accordance at the tempera¬ 
tures dealt "with, the boiling-point corrections being made. 
Octahedral Sulphur. —The observations were as follow for octahedral sulphur 
crystallized (and well dried) from carbon bisulphide 
