PoLLOK — The Vacuum Tube Spectra of some Metallic Vapours. 217 



towards the red. With the condenser the weaker band disappears, the other 

 is narrowed down, and a beautiful spectrum of chlorine is seen. The 

 remaining lines in the plate are those of tin, accidentally present, either on 

 the electrodes or in the chloride. 



Principal Ziiies of Aluminium. 



Chlorine. 



The spectrum of chlorine will be examined later, together with the spectra 

 of a number of electro-negative elements and their compounds, but it may be 

 stated now that liydrochloric acid gives the lines of hydrogen and chlorine, 

 and the author has failed so far to detect any extra lines other than those 

 due to the accidental presence of nitrogen or carbon, or the bands due to 

 water-vapour. The chlorine lines come out beautifully when the condenser is 

 used, especially if the gas is heated. With metallic chlorides the chlorine lines 

 hardly ever show unless the condenser is used, and they develop best when the 

 vapour is highly heated, but the lines are shown much more prominently with 

 some metals than with others. Thus, with the chlorides of arsenic, antimony, 

 aluminium, tin, and copper, the lines are well seen, but with the chlorides of 

 cadmium, zinc, bismuth, and mercury the lines of chlorine are not seen, or only 

 very faintly seen, under the conditions in which the present spectra were taken. 



SCIENT. PKOC. E.D.S., VOL. XIII., NO. XV, 



2 k 



