ARC IN AIR BETWEEN OTHER SUBSTANCES 59 



lengths with what is known as the "white" flaming arc. 

 The current was kept constant at 10 amperes. For com- 

 parison the corresponding curve for the open carbon arc as 

 plotted from Mrs. Ayrton's equation is given in curve d. 

 The great difference between the two forms of arc is very 

 evident. 



The data plotted in curve a were taken with the open 

 flaming arc having the carbons vertical, the positive one 

 being below. In general the flaming arc is enclosed in 

 some kind of a globe and usually with some arrangement 

 to produce a draft which will keep the ash from settling on 

 the globe. This curve, therefore, does not give the exact 

 voltage which would be needed when running under com- 

 mercial conditions. It does, however, give an approxi- 

 mate idea of such voltage. 



Observations were also made of the voltage with the 

 flaming arc enclosed in a globe which was very nearly air- 

 tight. The data thus taken are plotted in curve b. 



Observations were made with carbons which were pur- 

 chased from several different dealers and were supposed to 

 be different kinds of carbons. With one exception they 

 showed but slight differences as far as the potential differ- 

 ence at the terminals was concerned, so that the curves 

 given in Fig. 15 would apply fairly well to nearly all of the 

 carbons. The one exception gave higher voltages with the 

 longer arcs. For example, with an arc 22 mm. long the 

 voltage was 51 instead of 47 volts. 



The voltages required for the "yellow" flaming arc are 

 slightly less than those of the white arc. Such an arc is 

 represented by the curve c. 



In Fig. 1 6 there is given a curve showing the voltages 

 with different currents, the length being constant at 10 mm. 



