114 THE ELECTRIC ARC 



Alternating-current Arc between Metals. Mention 

 was made by Jamin and Maneuvier 1 in 1882 of alternating- 

 current arcs having a metal for one terminal and carbon 

 for the other, but, curiously, they make no mention of what 

 will occur when both terminals are metals. The difficulty 

 of maintaining such an arc was no doubt well known, but 

 the first observation to which I have been able to find a 

 reference was made by Wurts in 1892.2 He found that he 

 could not maintain such arcs between zinc, cadmium, 

 bismuth or antimony, even with large voltages. These he 

 called " non-arcing" metals. They are still often called 

 this, although the work of other experimenters would indi- 

 cate that they are no more non-arcing than* many other 

 metals. 



Arons 3 using an E.M.F. of 360 volts was unable to main- 

 tain such an arc between mercury, aluminum, copper, iron, 

 platinum, brass or nickelin. He believed that it would be 

 necessary to have an E.M.F. sufficiently high to start the 

 discharge each time with a spark. 



Similar observations were made by Granqvist 4 who be- 

 lieved that the difficulty was due to the fact that the heat 

 is rapidly conducted away by the metal. Steinmetz 5 

 states that it is necessary to have 500 volts in order to 

 maintain an alternating-current arc between magnetite 

 terminals and then it is very unsteady and the current 

 is partially rectified. In some experiments performed 

 by myself it was found that this form of arc could not be 



1 C. R., 94, 1615; 1882. 



2 Amer. Inst. Elec. Eng., 9, 102; 1892. 

 * Wied. Ann., 57, 195; 1896. 



4 Upsala Rom. Soc., p. i; 1903. Phys. ZS., 4, 537; 1903. Science Abs., 7, 

 40; 1904, and 10, 344; 1907. 



5 Trans. Intern. Elec. Cong., St. Louis, 2, 719; 1904. 



