146 New BesearcJies on Liquid Air. [March 27, 



free state approacli hydrogen in volatility. This view is confirmed 

 by the atomic refraction which Gladstone showed was 0*8 that of 

 hydrogen, and from which we may infer that the critical pressure of 

 fluorine is relatively small like hydrogen.* If the chemical energy 

 of fluorine at low temperatures is abolished like that of other active 

 substances, then some kind of glass or other transparent material 

 could be employed in the form of a tube, and its liquefaction achieved 

 by the use of hydrogen as a cooling agent. In any case a platinum 

 vessel could be arranged to test whether fluorine resists being liquefied 

 at the temperature of solid air, and this simple experiment, even if the 

 result was negative, would be of some importance. 



During the conduct of these investigations, I have gratefully to 

 acknowledge the able assistance rendered by Mr. Robert Lennox, my 

 chief assistant. Valuable help has also been given by Mr. J. W. 

 Heath. 



[J. D.] 



* On the other hand, the exceptionally small refractivity value observed by 

 Lord Eayleigh in the case of helium shows that the critical pressure of this body 

 is proportionately high. It would therefore bo more difficult to liquefy than a 

 substance having about the same critical temperature, but possessing a lower 

 critical pressure, like hydrogen. 



