LIQUID HYDROGEN. 133 



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 enabkxl him, by the use of Van der Waal's formula?, to cal- 

 culate the critical constants, and also the boiling point of liquid 

 hydrogen. 



Olszewski returned to the subject in 1891, repeating and correcting 

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

 using now a glass tube 7 millimeters in diameter instead of one of 2 

 millimeters, as in the early trials. He says: 



"On repeating my former experiments I had no hope of obtaining 

 a lower temperature by means of an\' 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 experiments Olszewski describes as follows: 



"The phenomenon of hydrogen ebullition, which was then observed, 

 was much more marked and much longer than during m}^ former 

 in^'estigations in the same direction. But even then I could not per- 

 ceive any meniscus of liquid hydrogen." 



Further: 



"The reason for which it has not hitherto been possible to liquef}^ 

 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 = l). Such a gas could be liquefied by means of 

 liquid ox3^gen 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 Wrol)lewski had done in 1885, only he employed a 

 platinum-resistance thermometer instead of a thermo-j unction. For 

 this purpose he used a small steel bottle of 20 or 30 centimeters capac- 

 ity', containing a platinum-resistance thermometer. In this wa^' the 

 temperatures registered were regarded as those of the critical and 

 boiling points of liquid h3drogen, 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 hj^drogen in the small steel 

 bottle. 



The results arrived at by Wroblewski and Olszewski arc given in 

 the following table, and it will be shown later on that Wroblewski's 

 constants are nearest the truth. 



Critical temperature. 



Boiling point 



Critical pressure 



Wroblewski, 



1885. 



—240° 



—250° 



13 atm. 



Olszewski, 

 1895. 



—234° 

 —243° 

 20 atm. 



