Gases of Atmospheric Air, and their Spectra. 209 



For separating the least volatile part of the gases, the vessel 

 E, with its contents, was dispensed with, and the tube o made to 

 communicate directly with that connected with the gauge, 

 sparking tube, and pump; and generally several sparking tubes 

 w r ere interposed between the gauge and pump, so that they 

 could be sealed off successively. The bulk of the liquid in B 

 consisted of nitrogen and oxygen. These were allowed grad- 

 ually to evaporate, the temperature of B being still kept low 

 so as to check the evaporation of the gases less volatile than 

 oxygen. When a great part of the nitrogen and oxygen had 

 thus been removed, the stopcock n was closed, and the tubes 

 partially exhausted by the pump, electric sparks passed through 

 g, and the gases examined spectroseopically. More gas was 

 then evaporated from B, and the spectroscopic examination 

 repeated from time to time. 



The general sequence of spectra, omitting those of nitrogen, 

 hydrogen, and compounds of carbon, which were never entirely 

 removed by the process of distillation alone, was as follows : 

 The spectrum of argon was first noticed, and then as the dis- 

 tillation proceeded the brightest rays, green and yellow, of 

 krypton appeared, and then the intensity of the argon spec- 

 trum waned, and it gave way to that of krypton until, as pre- 

 dicted by Range, when a Leyden jar was in the circuit, the 

 capillary part of the sparking tube had a magnificent blue 

 color, while the wide ends were bright pale yellow. Without 

 a jar the tube was nearly white in the capillary part, and yel- 

 low about the poles. As the distillation proceeded, the tem- 

 perature of the vessel containing the residue of liquid air 

 being allowed to rise slowly, the brightest of the xenon rays 

 began to appear, namely, the green rays about \ 5120, 5292, 

 and 4922, and then the krypton rays soon died out and were 

 superseded by the xenon rays. At this stage the capillary part 

 of the sparking tube is, with a jar in circuit, a brilliant green ; 

 and is still green, though less brilliant, without the jar. The 

 xenon formed the final fraction distilled. 



Subsequently an improved form of apparatus was used for 

 the fractionation. It is represented in fig. 2. A gasholder 

 containing the gases to be separated, that is to say, the least 

 volatile part of atmospheric air, was connected with the appa- 

 ratus by the tube a, furnished with a stopcock c. This tube 

 passed on to the bulb B, which in turn communicated through 

 the tube b and stopcock d with a sparking tube, and so on 

 through the tube e, with a mercurial pump. Stopcock d being 

 closed and c opened, gas from the holder was allowed to pass 

 into B, maintained at low temperature, and there condensed in 

 the solid form. Stopcock c was then closed and d opened, and 

 gas from B allowed to pass into the exhausted tubes between 



