NEW RESEARCHES ON LIQUID AIR. 



145 



per cent by volume in hydrogen is equivalent to some 13 per cent by 

 weight. 



The following table gives the theoretical temperatures reached for 

 an instant during the adiabatic expansion of hydrogen under different 

 conditions : 



Initial pressure (atmospheres) . 



500 (Pictet) 



300 (Cailletet).... 

 100 (Wroblewski) 

 180 (Olszewski) .. 



100 



200 



500 



Initial tem- 

 perature. 



Theoretical 

 final tem- 

 perature 



(absolute). 



o 

 —130 







25 







52 



—184 



24 



—210 



14 



—200 



19.5 



—200 



15.7 



—200 



12.7 



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

 sures. 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 bis 

 time to a laborious research on the isothermals of hydrogen at low tem- 

 peratures. The data thus arrived at enabled him, by the use of Van 

 der Waal's formula?-, to define the critical constants of hydrogen, its 

 boiling point, density, etc., and the subsequent experiments of Olszew- 

 ski have simply confirmed the general accuracy of Wroblewski's results. 

 Wroblewski's critical constants of hydrogen are given in the following 

 table : 



Critical temperature degrees . . — 240 



Critical pressure atmospheres . . 13.3 



Critical density . 027 



Boiling point degrees . . — 250 



Density at boiling point l . 063 



In a paper published in the Philosophical Magazine, September, 1884, 

 "On the liquefaction of oxygen and the critical volumes of fluids," the 

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

 and that instead of being 99 atmospheres, 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 Wroblew- 

 ski finding a critical pressure of 13.3 atmospheres, 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 difficut problem than 

 seeing the liquid in a glass tube under pressure and at a higher temper- 



1 It is probable that the real density of boiling liquid hydrogen may lie between 

 0.12 and 0.18. 



SM 96 10 



