Spectrum of Liquid Oxygen, 207 



appeared at the place of B. This had precisely the same 

 character as that at A ; that is, it had its sharp edge on the 

 less refrangible side and faded gradually on the more refran- 

 gible side. Its sharp edge also did not coincide with the 

 sharp edge of B, but reached nearly to the red potassium-line 

 X6913. By estimation, using the potassium-lines for com- 

 parison, we put the wave-length of the less refrangible edge 

 at about X6905, while its diffuse side was visible to about 

 A 6870, that is, barely to the place of the strong edge of B. 



It is plain that these two bands are related to each other in 

 the same way as the solar groups A and B are related, and 

 we cannot avoid the conclusion that they represent A and B, 

 but modified by the change of the absorbent from the gaseous 

 to the liquid state. 



If, as there is good reason to think, A and B are the ab- 

 sorptions of free molecules of oxygen, the persistence of these 

 absorptions in the liquid seems to show that the molecules in 

 the liquid are the same as in the gas. At the same time the 

 changes they undergo ought to throw some light on the 

 nature of the change in passing from the gaseous to the liquid 

 state, as well as on the causes which produce the sequences of 

 rays which are called channelled spectra. 



We have noticed, as Olszewski also has noticed, that liquid 

 oxygen is distinctly blue. This is, of course, directly con- 

 nected with its strong absorptions in the orange and yellow. 

 On looking at a mass of liquid oxygen through a direct-vision 

 spectroscope in any direction the scattered light shows the 

 strong bands plainly. Indeed they remain visible when the 

 oxygen has evaporated to the last drop, and they increase in 

 intensity as the liquid is cooled, so that when the pressure on 

 the liquid is reduced and the oxygen cooled by its own 

 evaporation to —200° they become exceedingly black. 

 Olszewski states that this blue colour is not, so far as he could 

 make out, due to ozone, and we are of the same opinion. 

 Ozone dissolves easily in liquid oxygen and imparts to it an 

 indigo-blue colour. Such a solution when poured into a 

 saucer of rock-salt assumes the spheroidal state, and as the 

 oxygen evaporates becomes more concentrated, and finally 

 explodes with considerable violence. In the dilute solution 

 we could not detect any absorptions due to the ozone. We 

 attempted to obtain a larger quantity of liquid ozone, or of a 

 concentrated solution, for the observation of its spectrum. 

 Oxygen oxonized in a tube cooled by solid carbonic acid gave 

 small beautiful cobalt-blue drops of liquid, but when a few of 

 these drops collected together in a tube immersed in liquid 

 oxygen to cool it to —181°, they exploded and blew the whole 



