MR. GROVE ON THE ELECTRO-CHEMICAL POLARITY OF GASES. 
95 
direction of the discharge, an intermediate condition is requisite ; so if the gas be not 
sufficiently attenuated the oxidation is too rapid, and the plate too much corroded to 
bring out the effects clearly ; if too much attenuated, too long a time is required and 
the effect is feeble and indistinct. 
I have above selected all the experiments which I consider material in this, I 
believe, new class of phenomena. The spots produced by electrical discharges, both on 
conducting bodies and on electrics, have been before noticed and experimented 
on, one class by Priestley*, and another class by KARSTEN-f- and others, but as far 
as I am aware no distinct electro-chemical action in dry gases, depending upon the 
antithetic state of the terminals and presenting a definite relation of the chemical to 
the electrical actions in gaseous media, has been pointed out. I now proceed to con- 
sider the relation which these results bear to other electrical phenomena. 
As may be gathered from my opening remarks, the experiments above detailed 
appear to me to furnish a previously deficient link in the chain of analogy connecting 
dielectric induction with electrolysis. The only satisfactory rationale which I can 
present to my own mind of these phenomena is the following. The discharges being 
interrupted (as is evident from the nature of the apparatus, and may be easily proved 
by agitating a mirror near them and regarding their reflected images in the moving 
mirror), the gaseous medium is polarized anterior to each discharge, and polarized 
not merely physically, as is generally admitted, but chemically, the oxygen or anion 
being determined to the positive terminal or anode, and the hydrogen or cation being 
determined to the negative terminal or cathode ; at the instant preceding discharge 
there would then be a molecule or superficial layer of oxygen or of electro-negative 
molecules in contact with the anode, and a similar layer of hydrogen or of electro- 
positive molecules in contact with the cathode, in other words, the electrodes in gas 
would be polarized as the electrodes in liquid are. The discharge now takes place, 
by which the superficial termini of metal or of oxide, as the case may be, are highly 
ignited or brought into a state of chemical exaltation at which their affinities can 
act ; the anode thus becomes oxidated, and the cathode, if an oxide, reduced. I 
have elsewhere:!; shown strong reasons for assuming that the electric or voltaic dis- 
charge, the moment polarity is subverted, may be regarded as an intensely heated 
state of the electrodes, and of the intermedium across wiiich it passes; and my 
present explanation is perfectly consistent with and derivable from my previous 
views of the disruptive discharge. 
Two other theories might be proposed to account for the phenomena I am con- 
sidering ; the one, that the disruptive discharge itself is analogous to the electrolytic, 
and that the oxygen and hydrogen are reciprocally transferred by the discharge 
itself; this would not, I think, be consistent with the generally known facts con- 
nected with the discharge, and is entirely ineffectual in explaining the experiments 
* History of Electricity, 2nd edition, p. 624. 
t Archives de I’Electricitd, vol. ii. p. 647 ; vol. iii. p. 310. 
+ Philosophical Transactions, 1847, pp. 10, 16, 21. Correlation of Physical Forces, p. 50, 2nd edition. 
