642 



SCIENCE. 



[N. S. Vol. XI. No. 278. 



cuted, before Wroblewski and Olszewski 

 succeeded in obtaining oxygen as a static 

 liquid, and to collect liquid hydrogen, 

 whicb is a much more difficult problem, 

 has taken just twenty j'ears from the date 

 of the Pictet and Cailletet experiments. 



Wroblewski made the first conclusive 

 experiment on the liquefaction of hydrogen 

 in January, 1884. He found that the gas 

 cooled in a capillary glass tube to the boil- 

 ing point of oxygen, and expanded quickly 

 from 100 to 1 atmosphere, showed the same 

 appearance of sudden ebullition lasting for 

 a fraction of a second, as Cailletet had 

 seen in his early oxygen experiments. No 

 sooner had the announcement been made, 

 than Olszewski confirmed the result by ex- 

 panding hydrogen from 190 atmospheres, 

 previously cooled to the temperature given 

 by liquid oxygen and nitrogen evaporating 

 under diminished pressure. Olszewski, how- 

 ever, declared in 1884 that he saw colorless 

 drops, and by partial expansion to 40 at- 

 mospheres, the liquid hydrogen was seen by 

 him running down the tube. Wroblewski 

 could not confirm Olszewski's results, his 

 hydrogen being always obtained in the form 

 of what he called a ' liquide dynamique,' 

 or the appearance of an instantaneous froth. 

 Olszewski himself seven years later repeated 

 his experiments of 1884 on a larger scale, 

 confirming Wroblewski's results, thereby 

 proving that the so- called liquid hydrogen 

 of the earlier experiments must have been 

 due to some impurity. The following ex- 

 tract from Wroblewski's paper states very 

 clearly the results of his work on Hydrogen : 



" L'hydrogene soumis a la pression de 180 

 atm. jusqu'a 190 atm., refroidi par I'azote 

 bouillant dans la vide (a la temperature de 

 sa solidification) et detendu brusquement 

 sous la pression atmospherique presente une 

 mousse bien visible. De la couleur grise de 

 c.ette mousse, ou I'ceil ne pent distinguer 

 des gouttelettes iucolores, on ne pent pas 

 encore deviner quelle apparence aurait 



l'hydrogene a I'etat de liquide statique et 

 I'on est encore moins autorise a preciser s'il 

 a ou non une apparence metallique. J'ai 

 pu placer dans cette mousse ma pile thermo- 

 electrique, et j'ai obtenu suivant les pres- 

 sions employees des temperatures de —208° 

 jusqu'a — 211°C. Je ne peux pas encore 

 dire dans quelle relation se trouvent ces 

 nombres avec la temperature reelle de la 

 mousse ou avec la temperature d'ebullition 

 de l'hydrogene sous la pression atmospher- 

 ique, puisque je n'ai pas encore la certitude 

 que la faible duree de ce phenomene ait 

 permis a la pile de se refroidir completement. 

 N6anmoins, je crois aujourd'hui de mon 

 devoir de publier ces resultats, afin de pre- 

 ciser I'etat actuel de la question de la lique- 

 faction de l'hydrogene."* 



It is well to note that the lowest ther- 

 mo-electric temperature recorded by Wro- 

 blewski during the adiabatic expansion of the 

 hydrogen (namely, — 211°) is really equiv- 

 alent to a much lower temperature on the 

 gas-thermometer scale. The most probable 

 value is — 2.30°, and this must be regarded 

 as the highest temperature of the liquid 

 state, or the critical point of hydrogen, ac- 

 cording to his observations. In a posthu- 

 mous paper of Wroblewski's on ' The Coni- 

 pression of Hydrogen,' published in 1889, 

 an account appears of further attempts 

 which he had made to liquefy hydrogen. 

 The gas compressed to 110 atmospheres, 

 wras cooled by means of liquid nitrogen 

 under exhaustion to —213.8°. By sud- 

 denlyreducing the pressure, as low a temper- 

 ature as — 223° on his scale was recorded, 

 but without any signs of liquefaction. This 

 expansion gives a theoretical temperature 

 of about 1.5° absolute in the gas particles. 

 The above methods having failed to pro- 

 duce static hydrogen, Wroblewski sug- 

 gested that the result might be attained by 

 the use of hydrogen gas as a cooling agent. 

 From this time until his death in the j'ear 



* Compt. Eend., 1885, 100, 981. 



