I 



Mr. Grove on the Electro-chemical Polarity of Gases. 513 



polislied rings, but of annuli of different degrees of oxidation, 

 were formed. 



When the experiment is continued for some time, a dark 

 deposit is formed on the glass around the extremity of the pla- 

 tinum wire, giving an extended conducting surface ; and this 

 may be the reason why such rings are formed, though these 

 rings, in all the cases which I have observed, differ broadly from 

 the rings formed by the bare needle or wire, not having the inter- 

 posed spaces of perfectly bright silver ; and in all the cases the 

 difference of effect produced by the coated and the bare wire is 

 very marked ; in by far the greater number of experiments, 

 when proper precautions are taken, not the slightest formation 

 of rings takes place with the coated wire ; with the bare wire, in the 

 gaseous mixture last mentioned, I have always seen them formed. 



Thus there are three systems of rings which may be formed 

 by the discharge. First, rings such as those seen in the ordinary 

 cases of thin plates ; these I have only observed with olefiant 

 gas, though probably there are many other conditions in which 

 they may be produced. Secondly, rings formed by the super- 

 position of layers of oxides, possibly arising from the fact that at 

 certain definite periods portions of the plate become by oxidation 

 inferior conductors, and other portions are attacked, and being 

 at a different distance undergo a different molecular change by 

 oxidation. Thirdly, and to me far the most interesting set of 

 phenomena are presented by the rings alternately bright and 

 oxidated, showing effects of oxidation and reduction by the same 

 current on the same plate, and which only take place in certain 

 gaseous mixtures, of which, uj) to this time, one volume oxygen 

 + five volumes hydrogen is the most efficient which I have 

 obtained. 



I cannot at present see any better mode of explaining these 

 phrenomena than by regarding them as analogous to the phseno- 

 mena of interference in light ; though doubtless if this be a right 

 view, the very different modes of action of light and electricity 

 would present very numerous phainomcnal distinctions. Alter- 

 nations of opposite polar electrical actions in the discharges pass- 

 ing in the same direction are, I think, very clearly shown in these 

 experiments, and this ap])ears to mc a result worthy of attention. 



Though acquainted with Nobili's Ijcautiful exj)criiiients on the 

 formation (;f coloured rings by deposition in electrolyzed licpiids, 

 yet as I was working on gases it did not occur to me to refer to 

 his memoirs*; I have done so since making the experiments 

 given in this postscript, and find that with regard to the rings 

 so formed by electrolysis, he suggests interference as a possible 

 explanation. 



The dark space in the discharge to which Faraday has called 



* Ann. de Ch. et de Phys. vol. xxxiv. 

 Phil. May. S. 4. No. 28. Snpjd. Vol. 4. 2 L 



