350 Mr. L. L. Campbell on 



The disintegration began from the large aluminium wire 

 back of the cathode disk, and the small portion of the cathode of 

 the tube (1) received the mirror deposit first. In about an 

 hour the large bulb B (fig. 1) was about half covered with a 

 bright opaque metallic mirror, showing interference colours. 

 During the disintegration process the cathode wire and 

 disk were covered with a fuzzy pink glow extending 1 to 

 2 mm. from the surface of the metal. No trace of chemical 

 action between the aluminium electrodes and the chlorine was 

 apparent to the eye. The discharge-tube was removed and 

 opened, and the deposit was examined in the usual way with 

 caustic potash, and was found to consist of aluminium metal. 



Disintegration in Bromine. — The bromine was prepared 

 by placing gold monobromide, AuBr, in the annex tube and 

 heating it gently. The bromide decomposes under normal 

 pressure at about 115° C. into Au and Br. The discharge- 

 tube was exhausted as in the case of chlorine, and a small 

 amount of bromine let in. The disintegration began, as 

 before, behind the cathode disk, and proceeded much as in 

 the case of chlorine, except that at the end of an hour the 

 deposit seemed greater than the deposit formed when 

 chlorine was used. The metal of the electrodes remained 

 bright during the disintegration, and no evidence of 

 chemical action was apparent. The metallic deposit when 

 examined proved to be aluminium. 



Disintegration in Iodine. — The iodine was prepared in the 

 annex tube from gold monoiodide, Aul, which decomposes, at 

 atmospheric pressure, at about 120° C. When the same 

 -condition of pressure was obtained in the discharge-tube as 

 was the case when chlorine was used, the disintegration 

 began and was very rapid. A white ring deposit was 

 formed in front of the metallic mirror. On examination 

 this was found to be aluminium iodide. This compound was 

 probably formed by the union of the metal and iodine after 

 the metallic particles had left the cathode. 



Relative Rates of Disintegration in the Halogens. 



The discharge was sent through two tubes connected in 

 series. The tubes were of the same dimensions, the one 

 contained chlorine and the other bromine. The cathode 

 dark-spaces in the tubes were kept of the same width as far 

 as practicable. Thus the pressure and voltage, as well as 

 the current strength, were the same in each tube. The 

 bromine tube received its mirror more rapidly than did the 

 chlorine tube, and after an hour the deposit in the former 

 tube seemed about twice as great as in the latter. 



