814 Mr. H. Smith on the Spectroscopy of the Electric 



quantity which arrives at the point increases till the current 

 (so far as it is due to the motion of the cations) is carried 

 entirely by the metallic ions, and none of it by the hydrogen 

 ions. After this, with constant current, no further increase 

 in the quantity of metal can take place at the negative 

 electrode, and the spectrum in consequence is at its maximum 

 brightness. The appearance of the spectrum at the positive 

 point in the strongest solutions is due to the current being 

 insufficient to remove the metallic cations from the neigh- 

 bourhood of the point. 



If an alternating brush (provided the solution is not too 

 weak) be examined in the rotating mirror, several bands, 

 occurring one after the other, will appear coloured, like the 

 negative brush, according to the salt in solution ; several 

 bands will then follow, coloured blue like the positive brush. 

 In the stronger solutions all the bands are coloured like the 

 negative brush. If a positive brush be produced at an 

 electrode which has just before been used in producing a 

 negative, it will appear for the first second or two coloured 

 according to the salt in solution. These experiments show 

 that the ions take some little time to accumulate at or be 

 expelled from the point. 



The solution spectrum is the only case where electrolysis 

 plays a definite and important part. 



Lithium Salts. 

 The lines which appear and are due to lithium are : — 



Principal Series. 



1st Sub-series. 



2nd Sub-series. 



6708 



6104 



4972 





4602 



4273 





4132 







3915 







3795 





The brightest line of the spectrum in the weaker solutions 

 was the red line \=6708. The lines of the 1st Sub-series, 

 X = 6I04 and A = 4602, approached it in brightness as the 

 strength of solution increased. Finally, the blue line 

 A, = 4602 became brighter than the red line nearest the 

 point. The red line was always the longest line in the 

 spectrum. An increase in current produced a similar effect 

 to an increase in concentration, but was not very marked. 

 This variation is most probably connected with the amount 

 of lithium liberated at the point. The line \— 6708 is the 

 ultimate ray of lithium persisting longest as the quantity of 



