ON THE ELECTRICAL PROPERTIES OF PURE SULPHUR. 
67 
by carbon and carbon gases differs very unexpectedly from reduction by hydrogen. 
Any alkaline selenide that might be formed is unimportant, because, firstly, it would 
be soluble in water, and, secondly, it is not stable in solution but deposits selenium, 
forming’, perhaps, some oxyacid of selenium. If this be the case, carbonic acid gas 
might liberate an oxide of selenium, but this would not volatilize at ordinary tem¬ 
peratures. It is possible, finally, that free selenium in the waste might gradually 
combine with the excess of lime, if there be an excess, and re-form selenide of 
calcium. This was tried by boiling finely powdered selenium with excess of lime—but 
no combination was produced during an hour, and operating on about half a gram of 
selenium. 
The case for the probable absence of selenium from Chance sulphur seems therefore 
to be pretty well made out, as well as for its absence from commercial thiosulphate 
of sodium. 
Other Methods of Purification. 
We have purposely omitted to use any method based on the crystallization of sul¬ 
phur from organic liquids or suljffiur dichloride. Our reasons are very simple —any¬ 
one who has crystallized sulphur from carbon disulphide must have noticed that on 
reducing such crystals to powder, even long after they have appeared perfectly dry, 
a strong and horrible smell, characterized by all the worst features of the odour of 
impure carbon bisulphide, becomes immediately perceptible. Since powdering the 
crystals reduces them only to smaller crystalline fragments, there is no reason why 
volatile compounds should not continue to linger in them. If this be the case, what 
are we to expect on distilling ? Surely it is gratuitous to assume that organic com¬ 
pounds could not be formed and distil with the sulphur. Supposing these compounds 
to be without smell, how could they be detected ? Again, carbon bisulphide is a 
liquid almost impossible to purify, it begins to decompose immediately under the 
action of light, and forms unknown compounds. Judging by the smell still clinging to 
some carbon disulphide very carefully prepared by one of us, we may hazard a guess 
that some selenium compound still lingered. As to toluene, turpentine, &c., con¬ 
sidered as solvents of sulphur, we have never seriously entertained the idea of using 
any of them, for fear of introducing volatile carbon compounds—and also because we 
have an idea that, owing to the comparatively small solubility of sulphur in these 
substances and the necessarily large amount of the solvent, traces of impurity might 
possibly accumulate in the sulphur. It surprises us that anyone conversant with, 
say, the curiously complex contents of rock crystals, should rely on crystallization to 
remove impurity. 
Worst of all possible solvents, in our opinion, is chloride of sulphur. Chlorine is 
most difficult to purify, and the process of preparation of chloride of sulphur involves 
uncertainties to which exception may be taken. Even supposing this solvent to be 
K 2 
