[ 202 ] 



XIV. Determination of the Critical and the Boiling Tempe- 

 rature of Hydrogen. By Dr. K. Olszewski, Professor of 

 Chemistry in the Unioersity of Cracow* . 



IN one of my previous papers f I have described a new 

 method of determining the critical pressure of gases, 

 which may be called the " expansion method," depending on 

 the fact that a gas under high pressure and at a temperature 

 not much higher than its critical temperature, assumes for a 

 moment the liquid state when the pressure is slowly dimi- 

 nished, this being manifested by the turbid appearance of 

 the gas always produced when the pressure is lowered to the 

 critical pressure of the gas experimented with. By means of 

 this method I thus showed that the previously unknown 

 critical pressure of hydrogen lies at 20 atm. In order to 

 verify this method I tested it on two other gases, viz. on ethy- 

 lene and oxygen, the critical pressures of which were accu- 

 rately known. I also mentioned that, until we know of other 

 cooling agents able to produce still lower temperatures than 

 is possible by means of liquid oxygen or air, the expansion 

 method will be the only one which allows us to determine 

 not only the critical pressure but also the critical temperature 

 of hydrogen. For if we could succeed by means of a very 

 sensitive apparatus in determining the temperature of hy- 

 drogen at the moment of its .expansion to the critical pressure, 

 at which the ebullition appears, this would doubtless be the 

 critical temperature of hydrogen. 



On again undertaking my researches, begun in 1891, I 

 proposed to measure the temperature at the moment of the 

 expansion of hydrogen by means of a thermo-electric junction, 

 composed of very thin copper and German-silver wires. But 

 several experiments performed in that direction soon proved 

 that a thermo-electric junction is not suitable for such experi- 

 ments, for the following reasons : — First, a junction composed 

 of two wires soldered together can never be thin enough to 

 assume instantaneously the temperature of the surrounding 

 gas. Secondly , at very low temperatures the junction rapidly 

 loses its sensibility, so that the deflexion of the galvanometer 

 cannot serve to measure the temperature in agreement with 

 the hydrogen thermometer. Then the measuring of low 

 temperatures by means of a thermo-electric junction is possible 



* Presented to the Cracow Academy on June 4, 1895. Communi- 

 cated by the Author. 



t Rozprawy (Transactions) of the Cracow Academy [2] iii. p. 385 

 (1891) ; also Phil. Mag. [5] xxxix. p. 199 (1895). 



