On the Liquefaction of Hydrogen and Helium. 257 



compression. My old experiments on the density of hydrogen in 

 palladium gave a value for the combined body of 0'62, and it will be 

 interesting to find the real density of the liquid substance at its 

 boiling point. Not having arrangements at hand to determine the 

 boiling point, two experiments were made to prove the excessively 

 low temperature 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 immersing the closed end in the liquid hydrogen, 

 the tube immediately fills, where it is cooled, with solid air. The 

 second experiment was made with a tube containing helium. 



The * Cracow Academy Bulletin ' for 1896 contains a paper by 

 Professor Olszewski, entitled " A Research on the Liquefaction of 

 Helium," in which he states " as far as my experiments go, helium 

 remains a permanent gas and apparently is much more difficult to 

 liquefy than hydrogen." In a paper of my own in the * Proceedings 

 of the Chemical Society,' No. 183 (1896-7), in which the separation 

 of helium from Bath gas was effected by a liquefaction method, the 

 suggestion was made that the volatility of hydrogen and helium 

 would probably be found close together just like those of fluorine 

 and oxygen. Having a specimen of helium which had been 

 extracted from Bath gas, sealed up in a bulb with a narrow tube 

 attached, the latter was placed in liquid hydrogen, when a distinct 

 liquid was seen to condense. A similar experiment made with the 

 use of liquid air under exhaustion in the same helium tube (instead 

 of liquid hydrogen) gave no visible condensation. From this 

 result it would appear that there cannot be any great difference in 

 the boiling points of helium and hydrogen. 



All known gases have now been condensed into liquids which can 

 be manipulated at their boiling points under atmospheric pressure 

 in suitably arranged vacuum vessels. With hydrogen as a cooling 

 agent, we shall get within 20 or 30 of the zero of absolute tem- 

 perature, and its use will open up an entirely new field of scientific 

 inquiry. Even as great a man as James Clerk Maxwell had doubts 

 as to the possibility of ever liquefying hydrogen.* No one can pre- 

 dict the properties of matter near the zero of temperature. Faraday 

 liquefied chlorine in the year 1823. Sixty years afterwards Wrob- 

 lewski and Olszewski produced liquid air, and now, after a fifteen 

 years' interval, the remaining gases, hydrogen and helium, appear as 

 static liquids. Considering that the step from the liquefaction of air 

 to that of hydrogen is relatively as great in the thermo-dynamic sense 

 as that from liquid chlorine to liquid air, the fact that the former 

 result has been achieved in one-fourth the time needed to accom- 

 plish the latter, proves the greatly accelerated rate of scientific 

 progress in our time. 



* See ( Scientific Papers,' vol. 2, p. 412. 



