1896.] 



on New Besearches on Liquid Air. 



143 



an instant during the adiabatic expansion of hydrogen under different 

 conditions : — 



The calculations show that little is gained by the use of high 

 pressures. The important inference to be drawn from the figures is 

 to start with as low a temperature as possible. 



From 1884 until his death, in the year 1888, Wroblewski devoted 

 his time to a laborious research on the isothermals of hydrogen at 

 low temperatures. The data thus arrived at enabled him, by the 

 use of Van der Waal's formulae, to define the critical constants of 

 hydrogen, its boiling point, density, &c., and the subsequent experi- 

 ments of Olszewski have simply cimfirmed the general accuracy of 

 Wroblewski's results. Wroblewski's critical constants of hydrogen 

 are given in the following table : — 



Critical temperature —240° 



„ pressure 13-3 atmos. 



„ density 0-027 



Boiling point -250° 



Density at boiling point * 0-063 



In a paper published in the Phil. Mag. September 1884, " On the 

 Liquefaction of Oxygen and the Critical Volumes of Fluids," the sug- 

 gestion was made that the critical pressure of hydrogen was wrong, 

 and that instead of being 99 atmos. (as deduced by Sarrau from 

 Amagat's isothermals) the gas had probably an abnormally low value 

 for this constant. This view was substantially confirmed by Wro- 

 blewski finding a critical pressure of 13*3 atmos., or about one-fourth 

 that of oxygen. The ' Chemical News ' (September 7, 1894) contains 

 an account of the stage the author's hydrogen experiments had reached 

 at that date. The object was to collect liquid hydrogen at its boiling 

 point in an open vacuum vessel, which is a much more difficult 

 problem than seeing the liquid in a glass tube under pressure and at 

 a higher temperature. In order to raise the critical point of hydrogen 

 to about — 200°, from 2 to 5 per cent, of nitrogen or air was mixed 

 with it. This is simply making an artificial gas containing a large 



* It is probahle that the real density of boiling liquid hydrogen may lie 

 between 0-12 and 0-18. 



