ATTAINMENT OF VERY LOW TEMPERATURES. 5 



that value be not too low. So that by expansions made, beginning 

 with the pressures of 80, 90, 100, no, 120, 130, 140 atm., the phenome- 

 non described constantly appeared at 20 atm. ; but if the initial pres- 

 sure was 70, 60 and 50 atm., the ebullition appeared at a lower and 

 lower pressure. ... 



" To ascertain the truth of this statement I performed two scries 

 of analogous experiments with gases, the critical pressures and tem- 

 peratures of which are accurately known, viz., with oxygen and 

 ethylene. The critical temperature of oxygen is, according to my 

 former researches, —118.8° and its critical pressure is 50.8 atm. In 

 the same apparatus which I used for the experiments with hydrogen I 

 cooled oxygen by means of ethylene boiling under atmospheric pressure 



. and subjected it to slow expansion beginning with initial pressures, 

 from 40 atm., up to 100 atm. The ebullition of oxygen always ap- 

 peared at a pressure of about 51 atm., provided the initial pressure was 

 not lower than 80 atm. . . . 



" I made similar experiments with ethylene, using the apparatus of 



Cailletet. ..." 



These experiments confirmed those made with oxygen, indicating 

 that this " dynamical method " is applicable to the determination of 

 critical pressures, though it would only be employed in cases, like that 

 ' of hydrogen, when no other course was possible. 



The next paper published in the same year* describes the applica- 

 tion of these results to the determination of the critical and boiling 

 temperatures of hydrogen. In place of the glass compression tube a 

 steel vessel containing a very thin-walled glass tube was employed, the 

 whole enclosing a resistance thermometer consisting of a very fine wire 

 of pure platinum wound on a frame of thin mica. The wire had a 

 diameter of 0.06 mm. ; its resistance was determined at the followmg 

 temperatures : 



„ ^ Resistance. 



Temperature. 



qO 1,000 ohms. 



— 78.2° ^°° 



— 182.5° 523 



— 208.3° 453 



The hydrogen was compressed into the steel apparatus, which was 

 cooled as in the previous experiment in liquid oxygen boiling under a 

 pressure of 15 mm., and the expansion was carried out m the usual 

 manner. The resistance of the coil was measured by means of a 

 Wheatstone bridge and reflecting galvanometer, and resistance m the 

 opposite arms of the balance was repeatedly adjusted, till on malang 

 the expansion no deflection of the galvanometer was observed. The 

 following results were obtained : 

 * Philosophical Magazine, 40, 202. 



