MR. GROVE ON THE ELECTRO-CHEMICAL POLARITY OF GASES. 
91 
surrounded the wire when the platinum was negative, was larger and more diffuse 
than with the other metals. 
5th. As air, notwithstanding its containing a great excess of nitrogen, gave an effect 
of oxidation at both electrodes, though different in degree, I increased the proportion 
of nitrogen by passing into the receiver nitrogen which had been formed by the slow 
combustion of phosphorus, the phosphorous acid having been well washed away, 
and potash being always in the receiver; no more air was allowed to be present 
than the very small quantity contained in the apertures of the stopcock ; with this 
mixture, viz. a maximum of nitrogen and a minimum of oxygen, and rarefied as 
before, a similar effect was produced to that shown in the mixture of air and hy- 
drogen, the positive plate being oxidated by the discharge, and the spot when made 
negative being reduced. The effect of reduction was not so rapid or so readily pro- 
duced 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 negative in a nitrogen vacuum, leaving, how- 
ever, a darker spot than that which was exhibited when they were reduced in 
hydrogen. Even when produced in an air vacuum, and then a very perfect exhaustion 
effected, such as would reduce the mercury in the barometer to the height of -^oth 
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 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 com- 
bine 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 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 experiment, it appeared to 
me that the mixture of atmospheric air and hydrogen was more efficient in exhibiting 
this phenomenon than 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 1 found to be a very efficient 
mixture. 
* Annales de Chimie, vol. bczxii. t Philosophical Transactions, 1843, pp. 110, 111. 
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