1900.] on Solid Hydrogen. 475 



liquid nitrogen must be isolated from the influx of beat by being 

 placed in a vacuum vessel, and the condensation of its vapour must 

 be effected by tbe use of liquid hydrogen. 



No boiling-out operation is necessary witb tbe cryopborus we aro 

 about to use. The apparatus is shown in Fig. 6. 1 he vacuum tube 

 B contains liquid nitrogen. It is fitted on by an indiarubber joint 

 to a wide piece of glass tubing doubly bent at right angles, A D ; and 

 in order to allow the gas from the boiling liquid to escape before the 

 experiment begins an aperture C is left which can be closed with 

 a stop-cock. On closing C, and inserting a part of the tube A into 

 a vessel containing liquid hydrogen, the gas within is condensed, and 

 thereby the pressure of the vapour in the interior of the vessel is 

 reduced, forcing the liquid nitrogen in the other part of the apparatus 

 to boil witb great violence. In a few minutes the temperature of the 

 nitrogen is so much reduced that it passes into the solid state. 

 Many other liquid gases might be used to replace the nitrogen in this 

 experiment. In making a selection, however, it is necessary to tako 

 only those bodits that possess a reasonably high tension of vapour at 

 the melting point. The process would not succeed easily with a sub- 

 stance like oxygen, that has no measurable tension of vapour in the 

 solid condition. 



In the autumn of 1898, after the production of liquid hydrogen 

 was possible on a small scale, its solidification was attempted by boil- 

 ing under reduced pressure. At this time, to make the isolation of 

 the hydrogen as effective as possible, the liquid was placed in a small 

 vacuum test-tube, placed in a larger vessel of the same kind. Ex- 

 cess of hydrogen partly filled the annular space between tbe two 

 vacuum vessels. On diminishing the pressure by exhaustion tho 

 evaporation was mainly thrown on the liquid hydrogen in the annular 

 space between the tubes. In this arrangement the outside surface of 

 the smaller tube was kept at the same temperature as the inside, so 

 that the liquid hydrogen for the time was effectually guarded from 

 influx of heat. With such a combination the liquid hydrogen was 

 evaporated under diminished pressure, yet no solidification took place. 

 Seeing experiments of this kind required a large supply of the liquid, 

 other problems were attacked, and further attempts in the direction of 

 producing the solid for the time abandoned. During the course 

 of the present year many varieties of electric resistance thermometers 

 have been under observation, and witb some of these the reduction of 

 temperature brought about by exhaustion was investigated. Ther- 

 mometers constructed of platinum and platinum-rhodium (alloy) were 

 only lowered 1^° C. by exhaustion of the liquid bydrogen, and they 

 all gave a boiling-point of —2-15° C, whereas the reduction in tem- 

 perature by evaporation in vacuo ought to be 5° C, and the true boil- 

 ing-point from —252° C. to —253° C. In the course of these 

 experiments it was noted that almost invariably a slight leak of air 

 occurred which became apparent by its being frozen into an air- 

 snow in the interior of the vessel, where it met the cold vapour of 

 bydrogen. When conducting wires covered witb silk have to pass 



