1899.1 



on Liquid Hydrogen. 



pressures, which ought to be applicable to boiling points under 

 reduced pressure. 



The resulting formula is — 



log._p = 7-0808 - = mm. 



(2) 



Now formula (1) gives a boiling point of 14 '2° absolute under a 

 pressure of 25 mm., whereas the second equation (2) gives for the 

 same pressure 15 *4° absolute. As the absolute boiling point under 

 atmospheric pressure is about 22°, both expressions lead to the con- 

 clusion that ebullition under 

 25 mm. pressure ought to re- 

 duce the boiling point some v. 



7° C. For some time experi- 

 ments have been in progress 

 with the object of determining 

 the temperature of hydrogen 

 boiling under about 25 mm. 

 pressure, by the use of the 

 platinum thermometer ; but 

 the difficulties encountered 

 have been great, and repeated 

 failures very exasperating. 

 The troubles arise from the 

 conduction of heat by the 

 leads ; the small latent heat of 

 hydrogen volume for volume 

 as compared with liquid air ; 

 the inefficiency of heat isola- 

 tion ; and the strain on the 

 thermometer brought about by 

 solid air freezing on it and 

 distorting the coil of wire. 

 In many experiments, the re- 

 sult has been that all the 

 liquid hydrogen has evaporated 

 before the pressure was re- 

 duced to 25 mm., or the ther- 

 mometer was left imperfectly 

 covered. The apparatus em- 

 ployed will be understood from 

 Fig. 2. The liquid hydrogen 

 collected in the vacuum vessel 



A was suspended in a larger vessel, of the same kind B, which is so con- 

 structed that a spiral tube joins the inner and outer test-tubes of which 

 B is made, thereby making an opening into the interior at C. The 

 resistance thermometer D and leads E pass through a rubber cork F, 

 and the exhaustion takes place through C. In this way the cold 



To Che pump 



Fig 



