101 
« 
No. V, salt in both carbons, upper carbon positive. 
No. VI, salt in both carbons, lower carbon positive. 
The following conclusions were arrived at: 
The arc is electrolytic. The electropositive elements seek the negative 
pole and the electronegative the positive pole. Hence the thickening of 
the metallic lines at the negative carbon. Convection currents due to 
heated gases in the are may be sufficiently strong to mask the true nature 
of the lines. 
In photograph No. IV the Ca lines were as strong at the lower nega- 
tive carbon as at the upper positive carbon, which contained the salt. In 
No. III 47 Ca lines appeared at the upper negative carbon and only 14 at 
the lower positive pole. The 14 were not due to the salt contained in the 
upper pole, but to impurities in the loewr carbon, for they were present 
when a plain carbon was substituted for the one containing the salt. The 
Ca traveled with, but not against, the current. 
Ca photographs were chosen to illustrate the above effects because they 
represent about an average for the elements experimented upon. Ti did 
not show the effects at all. The ines extended across the spectrum with 
almost uniform intensity. Sometimes they were slightly intensified at 
the positive carbon, probably because of the higher temperature. 
The Zn lines were slightly stronger at the negative carbon. The lines 
of Rb, K, Na, Li, Ba and Sr showed a much more decided preference 
for the negative pole than did the Ca lines. The preference was most 
marked in the case of Rb, though the most striking photographs were 
obtained with Ba, which has a large number of strong lines in this region 
of the spectrum. 
As far as it could be determined the order of the elements, as re- 
gards the tendency of their spectral lines to cling to the negative carbon, 
is the same as their order in the electropositive-negative series. 
The following experiment is more conclusive: The negative carbon of 
a horizontal are was filled with calcium chloride. A new plain carbon 
formed the positive pole. A horizontal arc was used, otherwise the heat 
convection currents might have thrown doubt upon the results of the ex- 
periment. The slit was horizontal and extended from pole to pole. The 
carbons were placed one cm. apart and an are was formed by passing 
between them a third carbon, which served to bring the poles in mo- 
mentary contact. After one minute the current was shut off, and the 
earbon containing the Ca was replaced by a new plain carbon. The are 
