1899.] on Liquid Hydrogen. 3 



thermals of hydrogen at low temperatures. The data thus arrived at 

 enabled him, by the use of Van der Waal's formulas, to calculate the 

 critical constants, and also the boiling point of liquid hydrogen. 



Olszewski returned to the subject in 1891, repeating and correct- 

 ing his old experiments of 1884, which Wroblewski had failed to 

 confirm, using now a glass tube 7 mm. in diameter instead of one 

 of 2 mm. as in the early trials. He says : " On repeating my former 

 experiments, I had no hope of obtaining a lower temperature by 

 means of any cooling agent, but I hoped that the expansion of 

 hydrogen would be more efficacious, on account of the larger scale 

 on which the experiments were made." The results of these experi- 

 ments Olszewski describes as follows : " The phenomenon of hydrogen 

 ebullition, which was then observed, was much more marked and 

 much longer than during my former investigations in the same direc- 

 tion. But even then I could not perceive any meniscus of liquid 

 hydrogen." Further, " The reason for which it has not hitherto been 

 possible to liquefy hydrogen in a static state, is that there exists no gas 

 having a density between those of hydrogen and of nitrogen, and which 

 might be for instance 7-10 (H = 1). Such a gas could be liquefied 

 by means of liquid oxygen or air as cooling agent, and be afterwards 

 used as a frigorific menstruum in the liquefaction of hydrogen." 



Professor Olszewski, in 1895, determined the temperature reached 

 in the momentary adiabatic expansion of hydrogen at low tempera- 

 tures, just as Wroblewski had done in 1885, only he employed a 

 platinum-resistance thermometer instead of a thermo-juuction. For 

 this purpose he used a small steel bottle of 20 or 30 cc. capacity, 

 containing a platinum-resistance thermometer ; in this way, the tem- 

 peratures registered were regarded as those of the critical and boiling 

 points of liquid hydrogen, a substance which could not be seen under 

 the circumstances and was only assumed 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 Olzewski are given in 

 the following table, and it will be shown later on that Wrob- 

 lewski's constants are nearest the truth. 



Wroblewski, Olszewski, 

 1885. 1895. 



Critical temperature -240° -234° 



Boiling point -250° -243° 



Critical pressure 13 atm. 20 atm. 



The accuracy of Wroblewski's deductions regarding the chief 

 constants of liquid hydrogen following from a study of the iso- 

 thermals of the gas is a signal triumph for the theory of Van der 

 Waals and a moDument to the genius of the Cracow physicist. 

 From these results we may safely infer that supposing a gas is 

 hereafter discovered in small quantity four times more volatile than 

 liquid hydrogen, having a boiling point of about 5° absolute, and 



b 2 



