ON THE ELECTRICAL PROPERTIES OF PURE SULPHUR 
63 
to any great concern. Above this point, unhappily, we are obliged to proceed by way 
of hypothesis, and so conduct the process of purification as to tend to eliminate 
impurities, which our general knowledge of the chemistry of sulphur leads us to 
suppose may be present in quantities too small for detection by chemical means. Only 
those impurities are to be feared which will distil with sulphur, or be mechanically 
carried over during distillation, and dissolve in carbon bisulphide. This practically 
narrows the investigation down to the consideration of selenium as an impurity. 
In order to cause any residual impurity to vary in different samples, we have tried 
a large number of different sources for our sulphur. Of these we retain three. The 
first is by decomposing commercial sodium-thiosulphate by pure hydrochloric acid, 
washing the deposited sulphur with platinum distilled water, and distilling till the 
residue on combustion is inappreciable. This method has the advantage of involving 
no contact with carbon compounds, and of giving rise to no impurities except those 
that are soluble in water, or left on distillation. As to the impurities which may be 
suspected to be present in the thiosulphate originally, these will be dealt with when 
we consider soda waste as a source of sulphur or thiosulphate. 
The second kind of sulphur which we have employed is that derived from the poly¬ 
sulphides of calcium. Some roll sulphur, in powder, was digested with marble-lime 
in the usual manner. The yellow liquor obtained was decomposed by pure hydro¬ 
chloric acid, and the precipitate washed and distilled. 
The third kind of sulphur is some recovered sulphur that came into our hands by 
the kindness of Mr. F. Wright, of Elliott Bros., importers of drugs in this city. 
We could get no information at all as to where it came from, or what the process of 
recovery was; but we were told that the sample (amounting to about 5 lbs.) was 
recovered and very pure. A very few trials showed us that, as far as the negative 
characteristics go, the claim of purity was well founded, for the sulphur was at least 
at good as our precipitated sulphur after about three distillations. To find out where 
it came from, with a view to investigating its history, we wrote to Mr. J. F. Chance 
(who was known to us as an authority on recovered sulphur) asking him whether he 
knew of any ordinary process by which sulphur of such a high degree of purity was 
produced commercially, and whether he could obtain a fresh supply for us. In reply 
Mr. Chance gave us a general account of the method of sulphur recovery invented by 
himself, and most kindly presented us with a large quantity of sulphur recovered by 
his process. On comparing this sulphur with that which we had received from 
Mr. Wright, it became obvious at once that the latter had been produced by the 
Chance process : the appearance alone is almost unmistakable. According to 
Mr. Chance, the moisture and non-volatile impurities amount together to not 
more than '01 per cent.—and the non-volatile impurities to perhaps only '001 per 
cent.—with regard to the latter number we can say that our experience roughly 
confirms this estimate, for we never obtained a weighable residue even from the 
evaporation of several ounces of the fused and filtered sulphur. Traces of selenium 
