LIQUEFACTION OF HYDROGEN AND HELIUM. 



261 



could not be seen under the circumstances, and was only assumed at 

 the most to exist for a second or two during the expansion of the gaseous 

 hydrogen in the small steel bottle. 



The results arrived at by Wroblewski and Olszewski are given in the 

 following table : 





Wroblewski, 1885. 



Olszewski, 1895. 



Critical temperature. . . 



-240° 

 -250° 

 13 at. 



-234° 

 -243° 

 20 at. 



Critical pressure 



The moment the critical point is approximately defined the boiling 

 point is roughly known , and the critical pressure can be inferred from 

 analogy with the behavior of other substances. 



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 Wroblewski 

 finding a critical pressure of 13.3 atmospheres, or about one-fourth of 

 that of oxygen. The Chemical News (Sept. 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 tem- 

 perature. 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 proportion of hy- 

 drogen which is capable of liquefaction by the use of liquid air. The 

 results are summed up in the following extract from the paper : " One 

 thing can, however, be proved by the use of the gaseous mixture of 

 hydrogen and nitrogen, namely, that by subjecting it to a high com- 

 pression at a temperature of —200° and expanding the resulting liquid 

 into air, a much lower temperature than anything that has been recorded 

 up to the present time can be reached. This is proved by the fact that 

 such a mixed gas gives, under the conditions, a paste or jelly of solid 

 nitrogen, evidently giving off hydrogen, because the gas coming off 

 I turns fiercely. Even when hydrogen containing only some 2 to 5 per 

 cent of air is similarly treated, the result is a white solid matter (solid 

 air) along with a clear liquid of low density, which is so exceedingly 

 volatile that no known device for collecting has been successful." 



The report of a Friday evening lecture on New Eesearches on Liquid 

 Air 1 contains a drawing of the apparatus employed for the production 



1 Proc. Roy. Inst., 1896. 



