PRESSURES GREATER OR LESS THAN ONE ATMOSPHERE 85 



The same experimenters give the following equations 

 when using carbon electrodes 4 mm. apart: 



In air E = 49.5 + 31. 5/7; in nitrogen E = 62 + 30/7. 



Grau and Russ 1 examined the arc in different gases for 

 small currents and with the distance of 5 cm. between 

 electrodes. The order of the gases when arranged with 

 respect to increasing potential differences was N 2 , air, CO, 

 SO 2 , O 2 , CO 2 and H 2 . The values for nitrogen varied from 

 3450 volts when the current was 0.05 ampere to 2075 volts 

 when it was 0.112 ampere. For hydrogen the value of the 

 potential difference varied from 6600 volts with a current 

 of 0.05 ampere to 5250 volts with a current of 0.121 ampere. 

 This was called by them an arc, but the values of both 

 the current and the potential difference are so different 

 from those of the ordinary arc that one would need to know 

 the magnitude of the cathode drop in order to decide 

 whether this should be called an arc or a spark. 



Experiments were performed by Weedon 2 on the arc 

 between water-cooled copper electrodes for the purpose of 

 determining whether there is any law regarding the elec- 

 trodes of the arc similar to Faraday's laws of electrolysis. 

 With such electrodes in air using a current of 2 amperes 

 for if hr. with a potential difference of 50 volts there was 

 a gain of weight of the anode of 0.023 > an d of the cathode 

 of 0.004 g- This is not more than -%-\-Q of the amount 

 which would have been transferred in electrolysis and this 

 is probably due to oxidation at high temperatures rather 

 than to any chemical action. 



. l ZS. f. Elektrochemie, 13, 345; 1907. 



2 Paper presented at the Electrochem. Soc., Washington, D. C., 

 April, 1904. 



