236 Prof. J. Dewar. Application of Liquid Hydrogen to the 



"This would give a density of almost inconceivable smallness. 

 Doubtless the supposition made above as to the rate of discharge is 

 very wide of the mark, being much too great. If the velocity of 

 rushing is about half the velocity of sound, the ratio of densities would 

 become 72 x 10 217 . If so it is satisfactory to find that the mathematical 

 following out of the hypothesis leads to a density of the residual air in 

 the vessel which is enormously below what suffices to account for the 

 observed result." A practical mode of rapidly attaining a high vacuum 

 in any vessel is to displace the air with carbonic or sulphurous acid, 

 either at the atmospheric or under diminished pressure, and then to 

 freeze out the remaining gas by the use of liquid air, just as in the 

 experiments with liquid hydrogen. 



The first vacuum tube was an electrodeless one, the air had not 

 been dried, nor the glass specially cleaned. On spectroscopic examina- 

 tion it showed hydrogen lines bright along with the second or compound 

 line spectrum of the same gas, and a series of bright bands defined on 

 the less refrangible side, diffuse on the more refrangible, which occur 

 in the yellow, green, blue, and indigo. These bands were found to be 

 identical with the carbonic oxide spectrum. With a Leyden jar in the 

 secondary circuit the line spectrum of hydrogen disappeared, leaving 

 the second spectrum fainter ; but the carbonic oxide bands remained 

 bright, and there was no appearance of the hydrocarbon spectrum. 

 The second tube had aluminium electrodes, and, like the last, had no 

 special treatment in filling in the air. This tube showed also the line 

 spectrum and the second spectrum of hydrogen; the latter being 

 bright along with the carbonic oxide spectrum ; but on sparking the 

 latter disappeared. No appearance of the hydrocarbon spectrum could 

 be detected, but there was a suspicion of bands in the indigo like the 

 negative pole spectrum of nitrogen. The addition of a Leyden jar 

 brought out nothing new, only intensifying the line spectrum of 

 hydrogen, while leaving the second spectrum bright. In neither of 

 the above tubes could any lines of nitrogen or oxygen be recognised. 

 The third tube was filled with air drawn over cotton wool, red-hot 

 copper oxide, and phosphoric pentoxide, no rubber joints being em- 

 ployed. The spectrum showed the carbonic oxide bands and the 

 hydrogen line spectrum as before. Only the second hydrogen 

 spectrum was feeble. There was a yellow line W.L. 5849, identical 

 with one occurring in the natural gas from the King's Well at Bath. 

 In a paper on " The Liquefaction of Air and the Detection of Impuri- 

 ties,"* the separation of helium from this gas is described by liquefac- 

 tion and fractionation, and it was observed that during the sparking 

 the helium lines were well marked along with "others, the origin of which 

 must be settled later" It was further observed, " With a modified form of 

 apparatus it will be possible to collect any residuary gas from the use not of 

 * ' Chem Soc. Proc.,' November, 1897. 



