Brush Discharge in Water and Salt Solutions. 469 



Observation of Spectra. 



The spectra I have observed in the brush and capillary 

 discharge are those o£ : — 



Hydrogen. — Series spectrum, and many-lined or secondary 

 spectrum. 



Oxygen. — Series spectrum, and many-lined or elementary- 

 line spectrum. 



Electrode. — Spark lines o£ platinum. These were observed 

 by Konen only in the condensed spark between two 

 platinum poles. 



Solute. — Complete spectrum, in visible part, of the metal. 



Impurities. — J) lines, red and green doublets o£ sodium; 

 blue line (X = 4227) and occasionally the red and 

 green bands of calcium. 



Hydrogen . 



The lines H a , EL, H of the series spectrum could nearly 

 always be discerned. Both this spectrum and the secondary 

 spectrum appear best in distilled water or very weak solutions. 

 In stronger solutions they are much feebler. This is best 

 shown by comparing PL V. fig. 1, a & b with fig. 3, a & b. 

 The insertion of a condenser has generally very little effect 

 on the series spectrum, but when the spark-gap is opened 

 the lines increase in brightness and begin to broaden. 

 With the heaviest discharges the lines are very broad and 

 bright, and a continuous spectrum stretches from the far 

 violet to beyond EL. If we compare one of these photo- 

 graphs, say fig. I, d. with the spectrogram of|the brush in 

 distilled water, fig. 6, 6, we see how relatively feeble H is in 

 the former compared with the increased brilliancy of H a . 

 Fig. 4, d and fig. 9 show this still better. 



The secondary spectrum of hvdrogen decreases in inten- 

 sity as the discharge increases. This is shown in the series of 

 spectrograms, PL Y. fig. 1, a, b, c, d, but best of all in the 

 series fig. 5. As these lines always appear very faintly at 

 the highest discharges, even in a series where they have not 

 been apparent in the uncondensed discharge (see PL V. 

 fig. 3), it would appear that they increase with the current 

 at a very much slower rate than the series lines. The decrease 

 shown in the photographs alluded to above is probably only 

 apparent, and due to the falling off in the number of sparks 

 per second. 



Comparing these results with the capillary discharge, we 

 find that a fine capillary (about *05 mm. diameter or less) 



