208 



Prof. K. Olszewski on the Critical and 



When the temperature of the hydrogen in the steel vessel 

 became equal to the temperature of the surrounding oxygen, 

 I made a slow expansion of the hydrogen to its critical pressure 

 (20 atm.), if I wished to measure its critical temperature, or to 

 the atmospheric pressure, if I wished to determine its boiling- 

 point. As the cooling of the platinum wire during the 

 expansion continued, the galvanometer returned to the zero- 

 point, if the resistance in the resistance-box was chosen so as to 

 be equal to the resistance of the platinum thermometer during 

 the- expansion. If in the first experiment the galvanometer 

 did not return precisely to the zero point, I varied the re- 

 sistances in the resistance-box, and repeated the experiment 

 till that return took place. I thus performed six series of 

 experiments : each of them was composed of about twenty 

 determinations of the critical and the boiling temperature of 

 hydrogen. 



As already mentioned, I used in these experiments three 

 platinum thermometers of different dimensions ; as cooling 

 agents I employed liquid oxygen boiling under a pressure of 

 18 to 12 millim.; in one series of experiments 1 used liquid 

 air, boiling under equally low pressure. The results I obtained 

 were always the same, and relatively very much in agreement 

 with one another, if we consider the great difficulty in per- 

 forming such experiments. The mean numbers, calculated 

 from many experiments, with reference to 1000 ohms at 0°, 

 were as follows : — 



Expansion of Hydrogen 

 from a high pressure to 



Resistance of 

 the Platinum 

 Thermometer. 



Temperature Extrapolated. 



20 atm. (critical pressure) 

 10 „ 

 1 ,., (atmospheric press.) 



383 ohms. 

 369 „ 

 359 „ 



— 234°5 (critical temperature) 



-239° 7 



— 243° - 5 (boiling temperature) 





On the basis of these numbers we can consider — 234°*5 

 as the critical temperature, and — 243°*5 as the boiling-point 

 of hydrogen. 



In a preliminary note, published in 'Nature'*, I gave 

 — 233° as the critical temperature, and — 243° as the boiling- 

 point of this gas. These numbers do not differ much from 



* 'Nature/ No. 1325, March 21. 



