474 Spectroscopic Study of the Electric Brush Discharge. 



of the capillary. For fig. 7, C the slit was narrowed and the 

 wire electrode was pushed right down till it reached nearly 

 to the bottom of the capillary. It is interesting to compare 

 this spectrum with fig. 1, b ; the red line of lithium (\ = 6708) 

 in each case is of about equal intensity. 



There can be little doubt then of the importance of the 

 point in the production of the lithium spectrum. As lithium 

 sulphate is a better electrolyte than lithium carbonate and 

 produces the lithium spectrum more readily, it seems sug- 

 gestive that the lithium accumulates close to the point due 

 to electrolytic action, being there vaporized and rendered 

 luminous. Unfortunately 1 was not able to test this point 

 further by examining a unipolar brush, but if the brush were 

 examined with a rotating mirror, at the feebler discharges, 

 one of the alternate bands was a deep red and the other blue. 

 This might easily have been due to the presence of the 

 lithium spectrum in the red band and its absence from the 

 blue. At the higher discharges the bands were the same 

 bluish colour — a result we would expect, considering the 

 relative feebleness of the lithium spectrum at the higher 

 discharges. 



Platinum. 



The spark-lines of platinum occur as the discharge through 

 the brush becomes heavy, and they increase with the intensity 

 of the discharge (see PI. V. figs. 1-4). In the uncondensed 

 brush in distilled water, as the water gets hotter the cm rent 

 and voltage drop, while the brush becomes feebler. The 

 various spectra of oxygen and hydrogen which appeared at 

 first grow fainter, and at length, when the water is on the 

 point of boiling, the platinum lines show up very faintly (see 

 PI. Y. fig. 6, c). 



Summary. 



The series spectrum of hydrogen in both the capillary and 

 brush discharge increases with increase of current density, 

 while the secondary spectrum decreases in relative intensity 

 to the series lines. The series lines broaden considerably 

 with the condensed discharges, and the relative intensity of 

 the lines falls off towards the violet. 



The series spectrum of oxygen appears only with the 

 higher current density discharges, being brighter with 

 higher current density. The elementary-line spectrum 

 appears in the brush with the feebler discharges onty, its 

 brightness also depending on the nature of the solution. It 



