PoLLOK — The Vacuum Tube Spectra of some Metallic Vapours. 215 



ArSEiNIC. 



The spark did not pass very readily with arsenic, and only with the very 

 greatest difficulty with chloride of arsenic ; with the sliglitest excess of vapour 

 tlie spark ceased to pass. In the vacuum tube spectra of the element the 

 lines of zinc are seen in addition to those of arsenic. The introduction of 

 the condenser did not make any difference to the arsenic lines, but appeared 

 to make it more difficult for the spark to pass with the chloride. Some of 

 the chlorine lines show without the condenser, which is unusual. Only a 

 comparatively small number of the arsenic lines show ; these, however, come 

 out quite strongly. 



Principal Lines of Arsenic. 



Antimony. 



With antimony the spark, as in the case of arsenic, passed with difficulty^ 

 and the luminescence in the tube was of a curious straw colour, due to many 

 lines in the orange that were easily seen by the hand spectroscope, though 

 they have not developed on the plate with the exposure given. To get good 

 photographs in this region would require much longer exposures, and this 

 would fog the rest of the plate. 



