1886.] Passage of an Electric Discharge through Nitrogen. 339 



This result shows that the decrease in pressure is not due to the 

 formation of a compound of nitrogen and platinum, a conclusion which 

 is confirmed by the fact that the decrease is independent of the ratio 

 of the volume of the electrode to that of the tube. The diminution in 

 the pressure is too large to be explained by supposing that it is due to 

 the formation of ammonia, which we know takes place when an 

 electric spark passes through a mixture of nitrogen and hydrogen, for 

 it would require at least 15 per cent, of hydrogen to be present to 

 produce a diminution in the pressure of the gas of from 8 to 12 per 

 cent., and we feel certain from the spectroscopic tests we have applied 

 to the gas that the quantity of hydrogen or hydrocarbon present is 

 extremely small, neither the hydrogen nor the hydrocarbon lines can 

 be detected at the pressure at which we work. Again, the gas is 

 restored to its original pressure by keeping it for some time at a 

 temperature just above 100° C, while ammonia is not decomposed 

 except at a much higher temperature. 



The combination of nitrogen and oxygen which takes place when a 

 spark passes through a mixture of the two gases is attended by a 

 diminution in volume, but we have calculated a superior limit to the 

 quantity of oxygen present, and find that it is very much too small to 

 explain the effects which we have observed in our tubes. 



It seems to us that the effect is too big to be explained as the result 

 of an impurity in the gas, and that the only hypothesis which agrees 

 with the facts is that we have an alio tropic modification of nitrogen 

 produced by the passage of the sparks. The formation of this is 

 quite analogous to that of ozone from oxygen, and we have found that 

 just as ozone is destroyed by continuous heating, so the diminution in 

 pressure which we have observed in nitrogen is permanently destroyed 

 if the tube be kept for some time at a temperature of 100° C. ; we 

 have not observed any tendency for the diminution in pressure to 

 disappear as long as the tube is kept at the temperature of the room, 

 about 15° C. The diminution we have observed seems to depend even 

 more than the formation of ozone on the kind of spark which passes 

 through the gas, and we are disposed to attribute partly at any rate 

 the great differences which we have observed at different pressures 

 to this fact, at some pressures it seems impossible to get quite the 

 right kind of spark. 



We have noticed that when the electrical discharge goes through 

 nitrogen whose pressure has been diminished by previous sparking, it 

 has a much greater tendency to produce a beautiful golden colour 

 than when it passes through a new tube. Exactly (as far as we can 

 judge) the same discharge which when it goes through a new tube will 

 produce a bluish-pink colour, will, when it goes through an old one in 

 which the pressure, has diminished, produce a peculiar yellow colour 

 between that of chamois leather and gold. 



