1904] On the Production of Helium from Bachum. 349 



Fig. 3. 



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through a comparison prism, when no doubt remained that the yellow 

 line was actually D 3 . By cooling the U-tube, the emanation and 

 dioxide were condensed, and the helium spectrum increased greatly in 

 brilliancy. After half an hour the tube was sealed 

 off. The position of the D 3 line was confirmed to 

 within one-tenth of the distance between the two 

 sodium lines, D 1 and D 2 . 



Experiment 2. — A second apparatus similar to the 

 last was made of entirety fresh glass, so as to exclude 

 any possibility of contamination with helium; and 

 the observation was repeated with 31*8 milligrammes 

 of radium bromide, kindly lent by Professer Euther- 

 ford, which had been kept in the solid state at least 

 3 months. The apparatus was slightly modified, as 

 shown in the dotted lines in fig. 2, so as to avoid 

 taking the gas through the pump.- As before, the 

 whole apparatus was washed out with oxygen, and 

 the copper spiral was glowed in oxygen, so as to 

 oxidise it superficially, and so render it able to deal 

 with the excess of hydrogen, as well as with the 

 constituents of the water which had been decom- 

 posed. After the gas had been admitted by opening 

 the stop-cocks G and H, the copper spiral was kept 

 glowing for three-quarters of an hour. The U-tube 

 was then cooled with liquid air, and tap D was 

 opened. D 3 was seen. Mercury was admitted to 

 the tubes D and C, and the vacuum-tube was sealed off. It now 

 showed all the visible helium spectrum except the faint least refran- 

 gible red, as well as the yellows, green, and violet of mercury. Two 

 unidentified lines were also measured, of approximate wave-length 

 6145 and 5675, the former faint but distinct, the latter moderately 

 bright. The vacuum tube did not glow visibly in the dark, showing 

 that the emanation had been almost completely removed. The U-tube 

 was next placed in communication with the pump, still surrounded 

 with liquid air, but no gas could be extracted; now the U-tube had 

 probably two or three times the capacity of the vacuum tube ; and at 

 the low temperature of liquid air, almost twenty times the quantity of 

 helium must have remained in it. It shone brilliantly in the dark. 

 The passage to the pump was then closed, and the liquid air removed. 

 On again establishing communication, a brilliant phenomenon was 

 observed in the dark ; the glowing emanation passed through the 

 capillary somewhat slowly, rushed along the wider connecting tubing 

 was delayed in passing through the tightly packed phosphorus 

 pentoxide, and finally filled the barrel of the Topler pump. On 

 raising the reservoir, the gas grew more luminous as its volume was 



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