94 
MR. GROVE ON THE ELECTRO-CHEMICAL POLARITY OF GASES. 
any other change, and on allowing the discharges to pass, formed the rings just as in 
the last experiment. 
15th. I examined some of the spots with an achromatic microscope, magnifying 
200 diameters ; I could not, however, discover any feature which the naked eye did 
not show, or any peculiar molecular state ; the polishing scratches on the plate were 
highly magnified, but the electrized spots only showed more dimly the colours or the 
lights and shadows which they exhibited to the naked eye. 
16th. I took the discharge on a silver plate in vacua of the following gases re- 
spectively.: — Oxygen, protoxide of nitrogen, deutoxide of nitrogen, carbonic acid, 
carbonic oxide and olefiant gas. 
The first four gases presented nothing remarkable, the plate was oxidated whether 
positive or negative, as in a vacuum of atmospheric air. In the protoxide of nitrogen 
the colour of the discharge was a beautiful crimson on both terminals. 
In deutoxide of nitrogen a greater tendency to reduction was shown wdien the 
plate was negative than in the other three gases, and there was also a tendeney to 
the formation of rings. In carbonic oxide the plate was oxidated when positive, and 
the oxide reduced when negative, just as with a vacuum of air and hydrogen, but 
rather more slowly; with a mixture of five volumes of carbonic oxide and one 
volume of oxygen, the rings were formed very distinctly, particularly if the plate was 
made negative first, and then positive. The luminous spot on the plate, when positive 
in this gas, was coloured green. 
When the plate was negative in olefiant gas it darkened, showing the rings of 
colour produced by thin plates, and very distinct from the other rings of which I 
have spoken. After a short time a pulverulent deposit was formed on the plate, 
giving brilliant sparks or stars of light which were not shown by any other 
gas. 
This deposit was too minute for analysis, but I have no doubt, from the gas used 
and the appearances presented, it was carbon. 
I have given in the above experiments the conditions under which they succeeded 
best; but upon repetition, although the exaet volumes of gases and other conditions 
were carefully attended to, they sometimes required a slight alteration to succeed, 
variations taking place from causes which I could not detect ; thus it was sometimes 
necessary to add a little more 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 
electrieian to have the results at his command. When there is too great a propor- 
tion 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 
