ARC IN AIR BETWEEN OTHER SUBSTANCES 



55 



The first mention which I have found of the arc be- 

 tween carbons in which other substances were mixed is 

 that in an article by Casselmann 1 who tried the effect of 



FIG. 14. 



introducing different salts into the arc and found that 

 they allowed longer arcs with the same number of cells. 

 He found that strontium nitrate, copper nitrate, and zinc 

 chloride were especially helpful in producing luminosity. 2 



1 Pogg. Ann., 63, 576; 1844. 



2 Other investigations were made by the following: 



Archereaus, C. R., 84, 137; 1877. 



Carre, C. R., 84, 346; 1877. 



Luggin, Centralbl. f. Elektrot, 10, 567; 1888. 



