272 Prof. L. Natanson on the Critical 



by some ten degrees. Now if the diffuse absorption-bands of 

 oxygen are produced by the molecules during their encounters 

 with each other in the gaseous and in the liquid states, it 

 might well be supposed that they would be profoundly 

 modified when the oxygen assumed the solid state. Hitherto 

 oxygen has not, when pure, been solidified, but liquid air is 

 readily brought to the solid state by rapid evaporation under 

 reduced pressure (Dewar, Proc. Roy. Inst., 19 Jan. 1894). 

 Whether the solid in this case is homogeneous or only a 

 magma of solid nitrogen mixed with liquid oxygen might be 

 questioned"*, but at all events it must contain oxygen at the 

 lowest temperature that can practically be reached. We 

 therefore tried whether we could detect any difference between 

 the absorptions of solid and liquid air. There was no differ- 

 ence that we could detect in the character of the absorptions, 

 and not much in their intensities. 



In order to test further the effect of temperature, we com- 

 pared the absorption of a thickness of 3 centim. of liquid 

 oxygen boiling under about 1 centim. pressure with that of 

 a like thickness of the liquid boiling at atmospheric pressure. 

 With the colder liquid the bands in the orange and yellow 

 were sensibly widened, mainly on the more refrangible side, 

 the faint band in the green was plainly darker, and the band 

 in the blue appeared somewhat stronger. The difference 

 between the temperatures of the two liquids may have been 

 about 17° C, which does not appear to be a great difference ; 

 but then it is nearly one fifth of the absolute temperature 

 of the warmer liquid. The increased density of oxygen at 

 — 200° C, according to Janssen's law, if extended to the 

 liquid state, should make the absorption greater by about 20 

 per cent, as compared with that at its boiling-point. 



XXII. On the Critical Temperature of Hydrogen and the 

 Theory of Adiabatic Expansion in the Neighbourhood of the 

 Critical Point. By Dr. Ladislas Natanson, Professor of 

 Natural Philosophy in the University of Cracow\. 



I. 



LET us consider a set of "ideal" gaseous bodies; the 

 fundamental assumption we shall adopt is that not 



* I have observed that solid air when placed in a strong magnetic 

 field has the oxygen sucked out of it towards the poles, so that there 

 seems little doubt that the solid air is only a magma of solid nitrogen 

 mixed with liquid oxygen. — J. D. 



t Abstracted from the Bulletin International de VAcademie des 

 Sciences de Cracovie, Mars et Avril 1895. Communicated by Prof. 

 Olszewski. 



