No. 6.] 



STUDY OF ARC SPECTRA. 



451 



Calcium lines photographed. 



Strontiimi Oxide. 



With strontium the arc has a pear-shaped purple center, the 

 larger end of which rests on the positive carbon. The central 

 part is bluish at each carbon. The outer sheath is of a brilliant 

 red color, and the line between the two parts is very sharp and 

 bright. The carbons are not very hot. They are, indeed, scarcely 

 more than at a red heat. The effect on the spectrum is similar to 

 that of calcium, and the same arrangement of lines at the positive 

 and negative carbon is emphasized. The band spectrum is about 

 as strong as when calcium is present, but it does not disappear 

 quite so completely as in the outer sheaths of the arc. 



The number of strontium lines in the vicinity of the bands 

 tends to obscure their character. 



