354 



Sir W. Bamsay and Mr. F. Soddy. 



[Apr. 14, 



was then completed until not a trace of a bubble passed through the 

 pump. The tap leading to the pump was closed, and that of the 

 burette opened, until the mercury had risen to near the bulb B. 

 On darkening the room the bulb B was brilliantly luminous : indeed, 

 it was possible to read a watch by its light. The liquid air was 

 allowed to evaporate away, and the reservoir of the burette lowered 

 and its tap opened ; by gently raising the reservoir the emanation 

 was all collected in the capillary tube A. The volume of the emana- 

 tion was read from day to day by help of a reading telescope. It 

 contracted regularly ; the tube was coloured deep purple after some 

 days, and this made reading difficult, but by a brilliant illumination 

 behind the rise of the mercury could be followed. No attempt was 

 made to pass a discharge for 28 days ; after that lapse of time the 

 emanation had contracted to a volume occupying only 0"! of a 

 millimetre of the capillary tube at a pressure of about 50 mm., yet 

 it maintained its brilliancy till the very last ; only the length of tube 

 illuminated grew shorter and shorter. On freezing out the mercury 

 vapour by cooling the bulb B with liquid air, the helium spectrum was 

 visible, and at the same time the effect of passing the discharge was 

 to reproduce gas in the capillary tube. 



After the conclusion of the experiment, the tip of the tube was cut 

 off immediately below the platinum wire, and the capillary depression 

 was measured at different levels. The capillary tube was then cut off, 

 and the volume determined by weighing with mercury ; it was then 

 calibrated by a shifting thread of mercury, under a reading microscope. 

 The final results were : — 



Time., Yolunie. Time. Volume. 



Start 0-124 cub. mm. 7 days 0-0050 cub. mm. 



lday 0-027 „ 9 „ 0-0041 



3 days 0-011 „ 11 , 0-0020 „ 



4 , 0-0095 „ ' 12 „ 0-0011 



6 „ 0-0063 „ 4 weeks ... 0*0004 



The comparatively large volume at the start is very remarkable ; we 

 can only record it, it may possibly have been due to the mercury 

 sticking in the capillary tube, which was narrower below. 



Experiment 5. — The former experiment was repeated, this time with 

 a regular capillary tube, of which the volume per centimetre was 

 0*24 cub. mm. It was regular in bore, and the depression due to 

 capillarity was 56*2 mm. of mercury. It was heated, as well as the 

 bulb in which the emanation was to be condensed, to incipient redness 

 during evacuation. The emanation was introduced, the accompanying 

 hydrogen pumped off, and the liquid air jacket removed. The volume 

 of the emanation was read at once, at different pressures. The follow- 

 ing table gives the lengths of the capillary tube, the corresponding 



