No. 6.] 



STUDY OF ARC SPECTRA. 



453 



Zinc Chloride. 



The band spectrum is better than was obtained under any other 

 circumstances. The bands are greatly extended and very distinct. 

 The arrangement of lines in different parts of the arc is especially 

 marked in the flame spectra. All of the calcium and aluminium 

 lines are very clear in the outer sheath of the arc and near the 

 negative carbon. The bands cling closely to the positive carbon, 

 but the zinc lines cross the arc with nearly equal brilliancy in all 

 parts. Only the carbon bands are seen in the region having a 

 wave length greater than X = 4862. 



The "grating effect" is continuous from X,= 3400. to X= 5635. 

 The effect of the zinc seems to be to obscure all but the 

 strongest of the other metallic lines, and to increase the intensity 

 of the band spectrum. 



Cadiuimn Chloride. 



The spectrum obtained when cadmium is present in the arc is 

 similar to that with zinc. 



