l6 ATTAINMENT OF VERY LOW TEMPERATURES. 



In my first experiments the hydrogen before entering the regen- 

 erator coil of the Hampson apparatus, which was cooled by making 

 liquid air in it, was passed through a coil immersed in solid carbonic 

 acid and alcohol ( — 78° C). The result was negative; indeed, it 

 appeared that the temperature of the inside of the apparatus began to 

 rise as soon as the hydrogen was allowed to expand in it, for on opening 

 the liquid air cock at the base of the apparatus the temperature of the 

 gas which escaped ceased after the first few minutes from being ex- 

 tremely cold. 



More than two months were spent in similar experiments with like 

 results. If, however, these experiments led to no immediate results, 

 they showed clearly that even though it might be theoretically pos- 

 sible to liquefy hydrogen by the method of free expansion without 

 employing liquid air as a cooling agent, it was practically essential to 

 cool the gas to the lowest attainable temperature before allowing it to 

 expand. This knowledge, and the experience in dealing with com- 

 pressed hydrogen, gained in the course of these experiments led me to 

 design an apparatus with which I was at once successful in obtaining 

 liquid hydrogen. The apparatus I constructed, with the assistance of 

 Mr. J. Holding, without whom I could not have carried on these re- 

 searches ; it cost but a few shillings, and after being slightly modified 

 it served me again in 19*02 in my researches on the properties of liquid 

 hydrogen. 



VII. The First Hydrogen Liquefier. 



This apparatus has been fully described in a paper read before the 

 Physical Society of London in November, 1900.* Fig. 3, A and B, 

 shows the general structure of the apparatus as first used, and the 

 modifications which were introduced into it for my later experiments. 



In the original form (A), the hydrogen, under a pressure of from 

 150 to 180 atmospheres, was first cooled to — 75° by passing through a 

 coil A immersed in a mixture of solid carbonic acid and alcohol. It 

 then passed through a coil contained within the central chamber B, 

 which, during an experiment, was continually replenished with liquid 

 air. The coil passed through the floor of the chamber B into a lower 

 chamber C, which communicated with an exhaust pump through the 

 pipe f. Liquid air was allowed to flow from B into C through a valve, 

 which was controlled from above by the lever h, and evaporating under 

 a pressure of 100 mm. reduced the temperature of the compressed gas 

 to below — 200°C. 



The gas then entered the regenerator coil D, which was much 

 shorter than in the Hampson air liquefier, being 180 mm. long and 50 

 mm. in diameter. The reason for taking: these dimensions will be dealt 



* Philosophical Magazine, 1901, p. 411. 



