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



gas, viz. one volume oxygen -f four hydrogen ; the plate being 

 positive and the needle j^ths of an inch over the centre of each 

 spot in turn, a ring of clear polish was formed rapidly in both 

 the dark discs, just at the distance where the ring of polish 

 appeared in the last experiment. I then exposed a clean portion 

 of the plate to the needle without 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 micro- 

 scope, magnifying 200 diameters ; I could not, however, discover 

 any feature which the naked eye did not show, or any pecvdiar 

 molecular state ; the polishing scratches on the plate were highly 

 magnified, but the electrized spots only showed more dimly the 

 colom's or the Ughts and shadows which they exhibited to the 

 naked ej-e. 



16th. I took the discharge on a silver plate in vacua of the fol- 

 lowing gases respectively : — Oxygen, protoxide of nitrogen, dcut- 

 oxide of nitrogen, carbonic acid, carbonic oxide and olefiant gas. 



The tii'st 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 when the plate was negative than in the other three 

 gases, and there was also a tendency 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 aii* 

 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, show- 

 ing 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 bril- 

 liant 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 

 exact volumes of gases and other conditions were carefully 

 attended to, they sometimes required a slight alteration to suc- 

 ceed, variations taking place from causes which I could not 

 detect; thus it was sometimes necessary to add a little more 



