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



This bubble seems to have little effect upon the spectrum 

 in general. In salt solutions when the brush is negative, 

 there is a brightening of the spectrum as a whole, especially 

 of the metal lines of the salt in solution and of the con- 

 tinuous background. Its formation is accompanied by a rise 

 in potential. 



In sulphuric acid, the bubble soon after its formation 

 becomes suffused with a beautiful violet colour, which com- 

 mences near the top and then spreads downwards till the 

 whole bubble is filled with the glow. This condition lasts 

 for a few seconds, when the bubble breaks up and the whole 

 process is gone through once more. Bubbles, similarly 

 coloured, occur in solutions of sulphates, hydrogen sulphide, 

 and sulphur dioxide. The intensity of the light emitted 

 depends upon the concentration of solution. In phosphoric 

 acid a luminous green bubble forms in the same manner. 

 In neither hydrochloric, nitric, molybdic, nor chromic acid 

 solution is the bubble coloured. 



Fig. 5. 



Bubble formation. In addition to discharge over top of 

 bubble, in Sulphuric Acid the whole bubble glows 

 with luminous violet colour. 



The diagrams fig. 2 to fig. 5 represent different types of 

 brush discharge. The separation of the bubble from the 

 point (fig. 5) is commented on in the previous paper. This 

 separation is best shown in the negative brush in sulphuric 

 acid. 



Electrical Conditions, fyc. 



The potential difference measured by the voltmeter gives 

 a mean value for what is actually a very variable quantity. 

 If the brush be examined in a mirror rotated quickly by 

 hand, it will be seen drawn out into luminous bands separated 

 by dark intervals during which no current is passing. Both 

 the negative and positive brush in distilled water appear as 

 continuous bands which are patchy and crossed with fine 

 lines. The negative brush in solutions appears as narrow 



