PRESSURES GREATER OR LESS THAN ONE ATMOSPHERE 83 



Arc in Other Gases than Air. There have been 

 a number of experiments performed on the arc in other 

 gases than air with no great agreement as to results. 

 About the only point on which there is agreement is that 

 it is more difficult to maintain an arc in hydrogen than 

 in air. 1 



In regard to the amount of potential difference needed 

 with the arc in hydrogen the following data have been 

 given. Arons could not maintain such an arc on a circuit 

 of 105 volts, unless the pressure of the gas was less than 

 one atmosphere. In some work by myself 2 it was found 

 that the voltage at the terminals of the arc was 100 volts 

 with the arc in hydrogen at a pressure of 70 cm. With 

 graphite terminals under the same conditions the voltage 

 was 130 volts. Stark, Retschinsky and Schaposchnikoff 

 give similar data for the carbon arc in hydrogen and some- 

 what larger values with the copper arc in hydrogen. 3 

 Malcolm and Simon using small currents and a distance 

 between the electrodes of 4 mm. give the equation E = 

 60 + 1 8o/7. 



With metals in hydrogen they found it impossible to 



1 Grove, Phil. Mag., 16, 480; 1840. 

 Matteucci, C. R., 30, 201; 1850. 

 Herwig, Pogg. Ann., 149, 523; 1873. 



Wilson and Gray, Proc. Roy. Soc., 60, 377; 1897. 



Arons, Ann. d. Phys., i, 700; 1900. 



Upson, Lond. Elec., 60, 58; 1908. Phil. Mag., (6), 14, 126; 1908. 

 S. P. Thomson states that the voltage of the arc in oxygen, nitrogen, 

 hydrogen and other gases was the same to within one volt, the current in each 

 case being 10 amperes. (Lond. Elec., 29, 460; 1892.) This result is so 

 different from that of all other experimenters that we must consider it 

 incorrect. 



2 Phys. Rev., 20, 374; 1905. 



3 Ann. d. Phys., 18, 223; 1906. 



