362 EXPERIMENTAL INVESTIGATIONS. 



of copper, silver, and platinum, and found the effect produced 

 by all and with nearly equal facility ; if there were any dif- 

 ference, the platinum point was the least efficient ; this may 

 be due to the peculiar effect of platinum in itself combining 

 the gases, or to its inoxidable character, the oxygen being 

 thrown off from its surface, and not uniting with it, as with the 

 more oxidable metals ; the flame or luminous appearance 

 which 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 phospho- 

 rous 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 released from 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 hydrogen, 

 the positive plate being oxidated by the discharge, and the 

 spot when made negative being reduced. The effect of reduc- 

 tion 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 negative in a nitrogen vacuum, leaving, 

 however, 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 -^ih 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 



