ELECTRO-CHEMICAL POLARITY OF GASES. 363 



the attenuated atmosphere, it was easy to take the discharge 

 in this mixture without producing detonation or any sudden 

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

 With this mixture the effect took place as with the mixture 

 of atmospheric air and hydrogen. I expected it to have been 

 more efficient, 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 polarisation and dis- 

 charge 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 case, f or whether any unknown 

 effect of nitrogen is concerned, I do not undertake to pro- 

 nounce ; I can only say that in several repetitions of the expe- 

 riment it appeared to me that the mixture of atmospheric air 

 and hydrogen was more efficient in exhibiting this phenomenon 

 that that of oxygen and hydrogen. 



8th. Different proportions of oxygen and hydrogen were 

 employed, and here also I found that within a tolerably wide 

 margin I could vary the proportion of the gases. Three 

 volumes of hydrogen to one volume of oxygen I found to be 

 a very efficient mixture. 



Qth. I now substituted for the silver plate plates of the 

 following metals : bismuth, lead, tin, zinc, copper, iron, and 

 platinum, 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. 



Lead oxidated easily, but the spot of oxide could with 

 difficulty be reduced. Tin, zinc, and copper required the 

 admission of a great quantity of air to produce oxidation ; and 

 I could not succeed in reducing the oxide by the electrical 

 discharge, at least so as to restore the polish of the plate ; a 

 blackening effect was in some degree produced. Iron was not 

 oxidated until the receiver was nearly filled with air, and then 



* Annales de Chimie, vol. kxxii. f Phil. Trans. , 1843, pp. no, III. 



