Mr. Grove on the Electro-chemical Polarity of Gases. 507 



hydrogen, sometimes a little more oxygen or air, to alter slightly 

 the state of attenuation in the gas, &c. 



The necessarily varying condition of the battery, and the state 

 of the contact breaker, slight impurities in the gases or on the 

 surface of the plates would be quite sufficient to account for these 

 irregularities. I mention them for the guidance of any one who 

 may wish to repeat the experiments ; a very little practice will 

 enable any electrician to have the results at his command. When 

 there is too great a proportion of air or oxygen, oxidation takes 

 place at both poles ; when too much hydrogen, reduction takes 

 place at both ; and to effect oxidation or reduction by reversing 

 the direction of the discharge, an intermediate condition is requi- 

 site ; so if the gas be not sufficiently attenuated, the oxidation is 

 too rapid, and the plate too much corroded to bring out the 

 eflFects 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 phsenomena. 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 Karstenf 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 consider the relation which these results bear to other elec- 

 trical phsenomena. 



As may be gathered from my opening remarks, the experi- 

 ments 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 o^\Ta mind of these phsenomena 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 ])olarized anterior to each dis- 

 charge, 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 con- 

 tact with the anode, and a similar layer of hydrog(;n or of electro- 

 positive molecules in contact with the cathode, in other words, 



* History of Electricity, '2nd edition, p. G2i. 

 t Archives de I' Electricity, vol. ii. p. 64/ ; vol. 



iii. p. MO. 



