294 J. Dewar — Boiling Point of Liquid Hydrogen. 



given by Boyle's law; there is a convenience, therefore, in this 

 form of Chappuis' formula for approximation, because T x can 

 quickly be calculated, and the correcting factor 6 can be 

 applied later if desired. 



In the first experiment (No. 1 of subjoined Table I) ther- 

 mometer No. 1 was filled with electrolytic hydrogen. The 

 initial pressure, (the pressure at 0° C.) was almost three-eighths 

 of an atmosphere, and was taken low in order to obviate any 

 complication from condensation on the walls of the reservoir. 

 Two other possible causes might abnormally reduce the pres- 

 sure at very low temperatures ; these were polymerisation and 

 the presence as impurity of small quantities of gases liquefying 

 above the boiling point of hydrogen. The measurement of the 

 density of the gas at its boiling point showed that there was 

 no polymerisation, and further proof of this was evident in the 

 constancy of the value of the boiling point when different 

 initial pressures were taken. To guard against the presence of 

 gases with a higher boiling point than hydrogen, the electroly- 

 tic hydrogen was allowed to pass continuously for eighteen 

 hours through the thermometric bulb before it was sealed off. 

 It was further calculated that an impurity of oxygen necessary 

 to reduce the boiling point of hydrogen by a degree would 

 amount to 3 per cent, a quantity too large to escape detection. 

 This experiment gave the boiling point of oxygen as — 182 0, 2, 

 and that of hydrogen as — 253°'0. 



In the second experiment (No. 2) a new thermometer, No. II, 

 was constructed with a much smaller value of a?, and as a fur- 

 ther protection against the presence of impurities, palladium- 

 hydrogen was employed as the source of the gas. A rod of 

 palladium, weighing about 120 grams, kindly placed at my 

 disposal by Mr. George Matthey, F.R.S., was charged with 

 hydrogen in the manner described in my paper " On the 

 Absorption of Hydrogen by Palladium at High Temperatures 

 and Pressures,"* and subsequently used as the source of supply 

 to fill the thermometer. The initial pressure was slightly less 

 than that in the first experiment; the corresponding results 

 were -182°-67 and -253°-37.f 



The new thermometer was filled afresh (No. 4) with palla- 

 dium-hydrogen at an initial pressure rather less than one 

 atmosphere, and gave for the boiling point of hydrogen the 

 temperature — 252°*8. This result is a confirmation of the 

 absence of polymerisation. 



The next step was to compare these results with the results 

 of similar experiments made upon another gas whose boiling 

 pQint fell within the range of easily determined temperatures; 



*Proc. Chem. Soc, 1897. 



fThis thermometer gave 99°-7 for the boiling point of water. 



