

Production of Vacua, and their Spectroscopic Examination. 237 



3 cubic feet of air or Bath gas, but from hundreds of cubic feet of such 

 products" The helium and other associated material was shown to be 

 more volatile than nitrogen. Pursuing this course of investigation in 

 the summer of this year, the volatile portion of air was examined, 

 when the presence of material giving the same lines as Bath helium 

 was recognised. While this investigation was in progress, Professor 

 Ramsay and Dr. Travers observed the same spectrum in the more volatile 

 portion of argon which they have associated with a new element called 

 neon. The use of liquid hydrogen, as described, proves that the most 

 characteristic line of neon in the yellow, about W.L. 5849, can be detected 

 in 25 c.c. of ordinary air, and the presence of helium in the atmosphere 

 is confirmed.* 



A fourth tube, filled like the preceding one, had a phosphoric pent- 

 oxide tube left on. This showed again the carbonic oxide bands, but 

 no hydrogen lines could be detected ; while the oxide of copper ought 

 to have removed all free hydrogen and transformed all the organic 

 matter into carbonic acid and water. Yet it appears that the 

 spectrum of the carbon compounds is difficult to remove from electrode- 

 less tubes, probably owing to carbonic acid coming from the glass. 

 There were some broad diffuse bands that may arise from the drying 

 agent. The absence of hydrogen in this tube suggests that its presence 

 in the third tube was due to vapour of water coming slowly from the 

 glass. I am greatly indebted to Professor Liveing for making a 

 careful examination of the spectra of these tubes. 



Sir William Crookes was good enough to prepare two tubes with 

 platinum electrodes, which he sparked in vacua till all hydrogen dis- 

 appeared, and then filled with dry air, but without the use of red-hot 

 copper oxide or any agent for the absorption of carbonic acid or the 

 destruction of organic matter. After the cooling with liquid hydrogen, 

 he found on spectroscopic examination, in one no hydrogen, but two 

 faint lines, one about 5852 W.L. and the other 5676 W.L. The 

 second tube showed the same yellow about 5852, the helium line 

 along with 5939 and 6145, the hydrogen lines C and F, and some red 

 lines. The observations of Crookes confirm the presence of neon, 

 helium, and hydrogen. The absence in his tubes of the carbonic oxide 

 spectrum is important, seeing all the electrodeless tubes gave this 

 spectrum. In these tubes the vacuum was very high, and it was 

 difficult to observe the gaseous spectrum. Still, the fact of finding hydro- 



"~ * In a paper along with Professor Liveing, " On the Spectra of the Electric 

 Discharge in Liquid Oxygen, Air, and Nitrogen," ' Phil. Mag.,' 1894, we noted that 

 during the distillation and concentration in vacuo of liquid oxygen and air under 

 diminished pressure that two bright lines appeared in the spectrum at wave-lengths 

 557 and 555, and that one of these lines was very near the position of the auroral 

 line. These lines are now attributed by the same chemists to a new element, 

 crypton. 



T 2 



