I 



Mr. Grove on the Electro-chemical Polarity of Gases. 503 



reduced. The effect of reduction was not so rapid or so readily 

 produced as when hydrogen was used, but was very decided. 



6th, With nitrogen, as much deprived of oxygen as I could 

 procure, the colours of oxidation were not exhibited, but a dark 

 spot apparently due to disintegration was produced, which was 

 not removed by the plate being made negative ; if, however, the 

 coloured spot was produced by the plate being made positive in 

 an air vacuum, they were removed by the plate being made ne- 

 gative in a nitrogen vacuum, leaving, however, a darker spot 

 than that which was exhibited when they were reduced in hy- 

 drogen. Even when produced in an air vacuum, and then a 

 very perfect exliaustion effected, such as would reduce the mer- 

 cury in the barometer to the height of ^V^b of an inch, the spot 

 was partially reduced when the plate was made negative. 



7th. An oxyhydrogen vacuum was formed, the gases being in 

 the proportion in which they form water ; and thanks to the 

 attenuated atmosphere, it was easy to take the discharge in this 

 mixture without producing detonation or any sudden combina- 

 tion of the gases, a possibility pointed out by Grotthus*. With 

 this mixture the effect took place as with the mixture of atmo- 

 spheric air and hydrogen. I expected it to have been more effi- 

 cient, but it was rather less so than the mixture of air and 

 hydrogen ; whether it be that the presence of nitrogen lessens 

 the tendency to combine of the gases oxygen and hydrogen, and 

 thus enables the electrical polarization and discharge to operate 

 more efficiently, whether . the nitrogen has a specific effect in 

 aiding the electro-chemical effect, as I have shown it has in one 

 peculiar casef, or whether any unknown effect of nitrogen is 

 concerned, I do not undeilakc to pronounce; I can only say 

 that, in several repetitions of the experiment, it appeared to me 

 that the mixture of atmospheric air and hydrogen was more 

 efficient in exhibiting this phajnomenon than that of oxygen and 

 hydrogen. 



8th. Different proportions of oxygen and hydrogen were em- 

 ployed, and here also I found that within a tolerably wide margin 

 I could vary the proportion of the gases ; three volumes of hy- 

 di'ogen to one volume of oxygen I found to be a very efficient 

 mixture. 



9th. I now substituted for the silver plate, plates of the fol- 

 lowing metals ; — bismuth, lead, tin, zinc, copper, iron and pla- 

 tinum, the former three metals being burnished, the latter 

 polished. 



Bismuth showed the effect nearly, if not quite as well as silver ; 

 it was oxidated in an air vacuum, reduced in a hydrogen vacuum, 

 and oxidated or reduced in the mixed gas according as it formed 

 the positive or negative terminal. 



* Annates de Chimie, vol. Ixxxii. t Phil. Trans. 1B43, pj). 1 10, 111. 



