136 LIQUID HYDROGEN. 



a thermo junction which gave entirely fallacioiis results, experiments 

 were made to proAC the excessively low tempiM-atiire of the boiling 

 fluid. In the first place, if a long piece of glass tubing, sealed at one 

 end and open to the air at the other, is cooled by inmiersing the closed 

 end in the liquid hydrogen, the tube immediately tills where it is cooled 

 with solid air. A small glass tube tilled with liquid oxA^gen when 

 cooled in liquid hydrogen is transformed into a bluish white solid. 

 This is a proof that the boiling point of hydrogen is nuich lower than 

 any temperature previously i"eached by the use of liquid nitrogen 

 evaporating in vacuo, seeing oxygen always remains liquid under such 

 conditions. A first trial of putting liquid hydrogen under exhaustion 

 gave no appearance of transition into the solid state. When the 

 vacuum tube containing liquid hydrogen is immersed in liquid air so 

 that the external wall of the vacuum vessel is maintained at about 

 — 190°, the hydrogen is found to evaporate at a rate not far removed 

 from that of licjuid air from a similar vacuum vessel under the ordinary 

 conditions of temperature. This leads me to the conclusion that with 

 proper isolation it will be possible to manipulate liquid hydrogen as 

 easily as liquid air. 



The boiling point of liquid hydrogen at atmospheric pressure in the 

 first instance was determined by a platinum-resistance thermom(>ter. 

 This was constructed of pure metal and had a resistance of 5.3 ohms 

 at 0° C which fell to about 0.1 ohm when the thermometer was 

 immersed in liquid h^'drogen. The reduction of this resistance to 

 normal air thermometer degrees gave the boiling points —2.38.2° and 

 —238.9°, respectively, b}^ two extrapolation methods, and —237° ])y a 

 Dickson formula.* The })oiling point of the liquid seems therefore to 

 be —238° C, or 35° absolute, and is thus about 5 higher than that 

 obtained by Olszewski by the adiabatic expansion of the compressed 

 gas and al)out 8° higher than that deduced by AA^roblewski from Van 

 der Waal's eijuation. From these results it may be inferred that the 

 critical point of hydrogen is al)out 50° absolute, and that the critical 

 pressure will probably not exceed 15 atmospheres. 



If we assume the resistance reduced to zero, then the temperature 

 registered by the electric thermometer ought to be —244° C. At the 

 boiling point of hydrogen registered by the electric-resistance ther- 

 mometer, if the law correlating resistance and temperature can be 

 pressed to its limits, a lowering of the boiling point of hj^drogen by 

 5° or 6° C. would, therefore, produce a condition of affairs in which 

 the platinum would have no resistance, or would become a perfect 

 conductor. Now. we have every reason to believe that hydrogen, like 

 other liquids, will boil at a lower temperature the lower the pressure 

 under which it is volatilized. The question arises, how much lower- 

 ing of the temperature can we practically anticipate? For this pur- 



^ See Philosophical Magazine, 45, 525, 1898. 



