168 Dewar — The Nadir of Temperature 



Art. XVII. — The Nadir of Temperature and Allied Prob- 

 lems • by James Dewar, LL.D., F.K.S. [Bakerian Lecture 

 (abstract) read before the Royal Society,* June 13, 1901.] 



1. Physical Properties of Liquid and Solid Hydrogen. 2. Separation of 

 Free Hydrogen and other Gases from Air. 3. Electric Eesistance Ther- 

 mometry at the Boiling Point of Hydrogen. 4. Experiments on the Lique- 

 faction of Helium at the Melting Point of Hydrogen. 5. Pyroelectricity, 

 Phosphorescence, etc. 



Details are given in this paper which have led to the follow- 

 ing results: — 



The helium thermometer which records 20 o, 5 absolute as the 

 boiling point of hydrogen, gives as the melting point 16° abso- 

 lute. This value does not differ greatly from the value pre- 

 viously deduced from the use of hydrogen gas thermometers, 

 viz., 16° *7. The lowest temperature recorded by gas thermom- 

 eter is 14° * 5, but with more complete isolation and a lower 

 pressure of exhaustion, it will be possible to reach about 13° 

 absolute, which is the lowest temperature that can be com- 

 manded by the use of solid hydrogen. Until the experiments 

 are repeated with a helium gas thermometer filled at different 

 pressures, with the gas previously purified by cooling to the 

 lowest temperature that can be reached by the use of solid 

 hydrogen, no more accurate values can be deduced. 



The latent heat of liquid hydrogen about the boiling point as 

 deduced from the vapor pressures and helium-thermometer 

 temperatures, is about 200 units, and the latent heat of solid 

 hydrogen is about 16 units. 



The order of the specific heat of liquid hydrogen has been 

 determined by observing the percentage of liquid that has to 

 be quickly evaporated under exhaustion in order to reduce the 

 temperature to the melting point of hydrogen, the vacuum ves- 

 sel in which the experiment is made being immersed in liquid 

 air. It was found that in the case of hydrogen the amount 

 that had to be evaporated was 15 per cent. This value, along 

 with the latent heat of evaporation, gives an average specific 

 heat of the liquid between freezing and boiling point of about 

 6. When liquid nitrogen was similarly treated for comparison, 

 the resulting specific heat. of the liquid came out 0*43 or about 6 

 per atom. Hydrogen therefore follows the law of Dulong and 

 Petit, and has the greatest specific heat of any known substance. 



The same fine tube used in water, liquid air, and liquid 

 hydrogen gave respectively the capillary ascents of 15*5, 2 and 

 5*5 divisions. The relative surface tension of water, liquid air, 

 and liquid hydrogen are therefore in the proportion of 15'5, 2, 

 0*4. In other words, the surface tension of hydrogen at its 



* From an advance proof received from the author. 



