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XXIII. On the Spectrum of Liquid Oxygen, and on the Refrac- 

 tive Indices of Liquid Oxygen, Nitrous Oxide, and Ethylene. 

 By Professors Liveing and Dewar*. 



IN September 1888 were described in this Magazine (p. 286) 

 the absorption-spectrum of oxygen gas in various states 

 of compression. At lower pressures the absorptions known 

 in the solar spectrum as A and B were most conspicuous, and 

 as the pressure increased the other bands described by 

 Jannsen came out with increasing intensity. The former 

 appear to be due to the molecules of oxygen, and increase in 

 intensity directly with the mass of the oxygen producing 

 them ; while the latter appear to arise from the mutual action 

 of the molecules on one another, since their intensity is 

 dependent on the density as well as the mass of the oxygen 

 producing them. 



With the small dispersion employed in these observations 

 the absorptions A and B were not resolved into lines as in 

 the solar spectrum, but they had otherwise the same general 

 characters : A consisted of two bands, and both A and B were 

 sharply denned on the more refrangible edge and gradually 

 faded out on the less refrangible side. Considering how 

 much more diffuse the lines forming these groups in the solar 

 spectrum become as the sun gets nearer the horizon (see 

 M^Clean's photographs), it is probable that, under the cir- 

 cumstances of our experiments, they would not have been 

 resolvable into lines even with higher dispersion. 



Subsequently, in a paper read at the Royal Society (Proc. 

 Hoy. Soc. vol. xlvi. p. 222), we described our observations on 

 the absorption of a thickness of 12 millim. of liquid oxygen. 

 We noticed, as Olszewski had done, the strongest three of the 

 diffuse bands seen in the spectrum of the compressed gas, 

 but could not detect A. The mass of oxygen in 12 millim. 

 of the liquid was not enough to make A visible. 



We have since made observations with larger quantities of 

 liquid oxygen. For this purpose we have used a glass tube of 

 the form shown at a in the annexed figure, about J inch in 

 diameter and 3 inches in length. This tube had the ends blown 

 as flat and clear as possible, and it was enclosed in a box with 

 glass sides bed, and the air in the box well dried, in order to 

 prevent the deposition of hoar-frost on the tube. The liquid 

 oxygen was poured into the tube at the pressure of the atmo- 

 sphere, and at first, of course, boiled violently, until the tube 

 was reduced to the temperature of boiling oxygen, — 181°, 



* Communicated by the Authors. 



