456 CAROLINE W. BALDWIN. [Vol. III. 



It might be thought that the changes observed were due to 

 the fact that the temperature is not high enough to render all 

 the lines visible. This view would be strengthened if the lines 

 of metals which require the highest temperature for fusing and 

 vaporization were strongest in those parts of the arc which are 

 hottest. But this does not seem to be the case, for although 

 K, Na, and Li, metals of low melting points, are strengthened at 

 the negative carbon, so also are Ba, Sr, and Ca, which have 

 relatively high melting points. The Cu and Ag lines extend 

 across the arc with nearly even intensity, and the same is true 

 of Zn and Cd. 



It does not seem that the diminished intensity of the carbon 

 bands in the presence of certain metals can be wholly due to 

 the density of the gases of the flame ; as there is no direct 

 relation between the amount of weakening of the bands and the 

 density of the metallic vapor. Neither does the change seem 

 to depend in any simple way upon the atomic weight of the 

 metals. Barium and potassium obscure the bands most ; and 

 they are respectively the highest and lowest in atomic weight of 

 the metals studied. 



There are many reasons for believing that there is an electro- 

 lytic action in the arc. This belief is strengthened by the fact 

 that the metallic lines appear at the negative carbon, and the 

 carbon bands are strongest at the positive. It is also true that 

 the metals K, Na, Li, Ba, Sr, Ca, which are highly electropositive, 

 are more strengthened at the negative carbon than are Cd, Zn, 

 Cu, Ag, which are less positive. 



In studying the effect of the metals upon the lines of the 

 original spectrum, we may consider the need of increased resist- 

 ance in the outer circuit to be due to diminished resistance of 

 the arc, or to a change in the counter electromotive force. In 

 the former case, the list of resistance given should have the 

 same order as the resistance of the various metallic vapors. The 

 arrangement, however, is not that of the respective metals as 

 we know them at ordinary temperatures. 



