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



current through the brash and a large decrease of potential 

 difference between the electrodes, the decrease being greatest 

 for the negative brush. When once the water has become 

 warm no amount of variation of the current in the trans- 

 former primary will restore the brush characteristic of cold 

 distilled water. 



The positive brush in cold distilled water is more silent 

 than the negative brush, though both make a hissing noise. 

 A steady stream of fine bubbles is ejected from the positive 

 point. The bubbles from the negative point are shot out in 

 a cloud from the brush and the water is kept in considerable 

 agitation. 



When the conductivity of the water is increased by the 

 addition of a little acid or some salt, the negative brush 

 changes into a short luminous tongue about 1 to 2 mm. long. 



Fiar. 3. 



Negative Brush in Solutions. 



It is unsteady, and does not appear to be separated into 

 filaments (fig. 3). In acids it emits a yellow light due to 

 some sodium salt present in solution as an impurity. In salt 

 solutions it emits a light according to the salt dissolved — red 

 for lithium salts, green for copper, blue for zinc, etc. The 

 positive brush is a little longer than the negative and much 



Fie-. 4. 



Positive Brush in Solutions. Discharge (A) in constant agitation. 

 Bubbles are emitted ironi apex B. 



broader, about from 2 to 3 mm. across. It consists of a pale 

 blue discharge spread over what appears to be the top of 

 a bubble, so that it has an umbrella-like shape (fig. 4}. 



