W. Skey. — On the Evolution of Sulphur from Carbon. 393 



acid in the way indicated is above it. Analogy cannot be always trusted as a 

 guide, though as a useful suggestor of probabilities it is unrivalled. 



As to the theory that the sulphide of iron in the carbon or graphite used 

 is concerned in the production of this gas, Mr. Highton himself appears to 

 have thoroughly settled this by proving that sulphuretted hydrogen is not 

 generated when the poles of his battery are unconnected, sulphide of iron being, 

 as is well known, decomposed with evolution of this gas on the mere contact 

 of sulphuric acid with it, and this would of course go on with still more 

 energy and rapidity when the iron compound is in juxtaposition with a 

 negative substance, as carbon. 



Having thus endeavoured to show the inability of either of these two 

 theories to explain the phenomena described, I will now proceed to the next one, 

 which is that I have always held and now hold upon this subject, viz., that 

 the gas in question is derived, as to its sulphur at least, from the carbon itself. 



I base this conclusion upon the following data : — 



(1.) The metallic nature of graphitic carbon. 



(2.) Its so termed absorptive power for sulphuretted hydrogen. 



(3.) The probability that this power has been exercised by the graphite 

 used by Mr. Highton. 



(4.) The decomposition of metallic sulphides generally when connected 

 voltaically with easily oxidizable metals. 



(5.) That sulphuretted hydrogen is not evolved voltaically from charcoal 

 free from sulphur, if the exciting acid, whether sulphuric or hydro- 

 chloric, is pure. 



Of these data the only ones requiring consideration here, as not being 

 already treated or detailed, is the metallic nature of carbon, and (in relation to 

 the absorptive power of this substance for sulphuretted hydrogen) the form in 

 which this gas or its sulphur is absorbed. 



That carbon in the graphitic state is a metal has long since been promul- 

 gated, and without, as I believe, eliciting any controversy of a nature at all 

 subversive to such an idea, indeed its relations when in this state, both to light 

 and electricity, are so precisely those of metals generally to these forces, that, 

 according to the manner by which we as yet distinguish metals from metalloids, 

 we cannot avoid accepting this idea. Graphite, the substance here in view, is 

 not, as we know, pure carbon, but it certainly bears the same relation to light 

 and electricity as pure graphitic carbon does ; therefore we may, I think, 

 correctly class it as a metal too (though an impure one) and possibly sustain- 

 ing the same relations to pure graphitic carbon as hydrogenized palladium 

 bears to pure palladium, both metals being impure although truly metallic. 



Now, as to the form in which H^S is absorbed by charcoal — that is, as we 

 have seen, by impure metallic carbon — it is well known that those metals which 



b2 



