of Metallic Vapours in Electric Sparks. 353 



magnesium, aluminium, zinc, tin, and lead. These metals give 

 bright spots on both electrodes and there are differences between 

 the spectra of these. The spectra of the anode spots on magnesium 

 and aluminium contain the " oxide bands " of the metals, but 

 these bands have not been observed in the kathode spots. The 

 writer is continuing the study of this subject in the hope of 

 gaining further knowledge on the constitution of electric sparks 

 and the origin of the spectra. 



Note. Since the above paper was written it has been found 

 by examination of the sparks in a rotating mirror that the coloured 

 flames actually shoot out from the kathode. There was practically 

 no colour given to the spark by the matter thus expelled in an 

 atmosphere of hydrogen ; colours were obtained in some instances 

 in nitrogen but the experiments are not yet concluded. The 

 spectra of the bright spots on the kathodes are always brighter in 

 hydrogen than in air or oxygen and they are usually brighter 

 under pressures somewhat below the ordinary atmospheric pressure. 

 Zinc and cadmium were reduced from electrodes of their oxides 

 when these were in hydrogen. Their vapours were shot off from 

 the electrode and films of the metals condensed in the form of 

 rings on the tube and on pieces of perforated mica placed in the 

 path of the spark. 



