4 ATTAINMENT OF VERY LOW TEMPERATURES. 



statique et ron est encore moins autorise a preciser s'il a ou non una 

 apparence metalliqiie. 



" J'ai pu placer dans cette mousse ma pile thermo-electrique et j'ai 

 obtenu suivant les pressions employees des temperatures de — 208° 

 jusqu'a — 2ii°C." 



The last statement shows clearly that little weight can be attached 

 to these experiments. 



Professor Wroblewski's more important work consisted in an in- 

 vestigation of the isothermals of hydrogen at low temperatures, under- 

 taken with a view to the calculation of the critical constants. In this 

 work he was engaged at the time of his death, which occurred in 

 1888 through an accident with a paraffin lamp. The results were 

 fortunately ready for publication, and appeared shortly afterwards in 

 the Sitzungsberichte of the Vienna Academy (October 25, 1888). 

 The following values for the critical constant were calculated by 

 means of an equation of the " Clausius " form : 



Critical temperature — 240.4° C. 



Critical pressure — 13.3 atm. 



Critical volume 0.00335 c.c. 



An exhaustive account of Professor Olszewski's later experiments 

 on the liquefaction of hydrogen has been published by him in the 

 Philosophical Magazine for 1895.* The paper also contains a gen- 

 eral account of his researches on liquefied gases. The following is an 

 account of his attempt to liquefy hydrogen. 



Pure hydrogen was compressed into a glass tube 1 1 mm. in external 

 diameter and 7 mm. in internal diameter, containing a very thin-walled 

 glass tube, 6 mm. in diameter, to isolate the hydrogen from the warmer 

 walls of the larger tube. The apparatus was cooled with liquid air 

 boiling under less than 10 millimeters pressure. The remaining opera- 

 tions are described by the author in the following words : 



" I introduced hydrogen into the tube by slowly opening the cock 

 on the cylinder (which contained pure hydrogen under pressure) till 

 the pressure rose to 140 atmospheres. When the hydrogen in the tube 

 had come down to the temperature of the cooling agent, I little by little 

 produced expansion by opening the screw-cock. The phenomenon of 

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

 and much longer than during my former investigations in the same 

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

 hydrogen. 



" I have remarked in these experiments that with a slow expansion 

 the phenomenon of sudden ebullition always appears under the same 

 pressure, no matter how great the initial pressure may be, provided 

 *Vol. 39, p. 188. 



