1889.] Absorption- Spectra of Oxygen and its Compounds. 225 



cause of this may be that the development of the diffuse bands 

 depends in some degree on the total pressure of the air, and not only 

 on the partial pressure of the oxygen in it. 



The mass of oxygen which when unmixed with nitrogen made 

 A visible would correspond to that in the tube filled with air at 

 5 atmospheres, and that which made B visible would correspond to air 

 at 10 atmospheres. The differences between these pressures and those 

 which are actually needed to render A and B visible seem too great 

 to be ascribed to errors of observation, and seem to indicate that the 

 addition of the nitrogen has some effect on the absorptive action of 

 the oxygen. On the other hand, Egoroff found that he could still 

 distinguish A when the thickness of air at ordinary pressure was 

 reduced to 80 metres (< Compt. Rend.,' vol. 101, p. 1144). This 

 amount of air corresponds to rather less oxygen than our tube would 

 hold at a pressure of 1 atmosphere. Differences in the sources of 

 light, in the spectroscope, and the observers, would, however, count 

 for a good deal in observations of this kind. 



In order to try the influence of temperature on the absorption, the 

 shorter of our experimental tubes, 165 cm. long, was surrounded 

 by a jacket filled with a mixture of solid carbonic anhydride and 

 ether, which was rapidly evaporated by means of a large air-pump. 

 By this means the temperature would be reduced to —100°. The 

 absorption of oxygen at several different pressures up to 104 atmo- 

 spheres was observed through the cooled tube. We were not, however, 

 able to 'detect any increase of intensity, or other change, in the 

 absorptions which could be ascribed to the cooling. To try the effect 

 of an increase of temperature, the 18-metre tube was surrounded by a 

 jacket and heated up to 100° by steam. Heating appeared to render 

 the diffuse bands rather more diffuse and less distinct. On the whole 

 the influence of a change of temperature of 100° either way is 

 slight. 



We have observed repeatedly the absorption of liquid oxygen in 

 thicknesses of 8 and 12 mm. Our observations confirm those of 

 Olszewski. 8 mm. of liquid oxygen gives plainly the three diffuse 

 bands above C, D, and ¥, respectively. With a thickness of 12 mm. 

 we were not able to detect any more. 



We observed the absorption produced by liquid oxygen on the one 

 hand when it was cooled by its own evaporation until the tension of 

 its vapour was only equal to that of the atmosphere, that is, to a 

 temperature of —181°, according to Olszewski, and also when the 

 temperature of the liquid was allowed to rise under pressure up to 

 nearly the critical temperature. There appeared to be no appreciable 

 difference in the absorption under these different circumstances when 

 the oxygen was completely liquid, when it was near its critical 

 temperature, and when it was completely gaseous; so far at least as 



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