562 



1. Cathodic Luminescence. (Wehnelt interruptor, 

 Chromoscope of v. Bolton.) 



^ 2. The first data about phenomena of" light at tlie anode, as 

 they appear in the WEHNEi.T-interriiptor, were given by Wehnelt 

 (6) himself. Voller and Waltheh found (7) that much stronger light 

 effects are obtained when tlie smaller electrode is made cathode, 

 hence when the interruptor is inserted reversel}'. A very pure 

 spectrum of the electrode metal is then observed, and further some 

 of the hydrogen lines appear. The phenomena also occur when the cell 

 is not inserted as an interruptor, hence without induction coil. 



Without taking these observations sufficiently into account, v. 

 Bolton (8) later described an arrangement which was suitable for 

 spectralanalytic purposes and closely resembled the preceding one. 

 He called this arrangement "Chromoscope". As anode served a 

 thick platinum wire or platinum plate; as cathode he used a pla- 

 tinum wire, or a rod of the metal that was to be examined spectro- 

 analytically. The electrolyte (H,SO,, or better HNO, 1:4) contained 

 in the first case a small quantity of the substance to be examined. 

 When the current is closed by carefully immersing the cathode, 

 very clear and pure spectra of the metals are obtained, which are 

 present as electrode or in the electrolyte, and besides H-lines (espe- 

 cially Ha) and the Na-D-line. v. Bolton used a potential of 110 

 Volt; then the strength of the current in his electrolyte-chromoscope 

 amounted to 0,15 — 0,3 Amp., in his metal chromoscope to 2 Amp. 



Morse (9) investigated the light of the WEHNELT-interruptor more 

 closely. He used an alternate current of a pretty considerable 

 strength, and found that cathode and anode give the same spectrum; 

 the cathodic light was, however, much stronger than the anodic 

 light. He did not observe H-lines. The spectra obtained sometimes 

 resembled the arc-spectrum more closely, sometimes the spark spec- 

 trum, without his being able to give a satisfactory explanation of 

 this. There are, however, always characteristic differences between 

 Wehnelt- and spark-spectra, resp. Wehnelt- and arc-spectra. We 

 shall come back to further observations of Morse later on. 



For the investigation of the cathode spectra the arrangement of v. 

 Bolton is the most suitable; this was still somewhat modified for 

 experiments of longer duration. Fig. 1 represents a simple model of 

 an electrolyte-chromoscope, with which experiments can be made 

 without difficulties. A f/-tube is placed within a cooling-jacket; 

 the legs of this tube are closed by two rubber stoppers, in which 



