4: Professor Dewar [Jan. 20, 



therefore incapable of direct liquefaction by the use of liquid hydro- 

 gen, yet by a study of its isotbernials we shall succeed in finding 

 out its most important liquid constants, although the isolation of the 

 real liquid may for the time be impossible. 



In a paper published in the ' Philosophical Magazine,' September 

 1884, " On the Liquefaction of Oxygen and the Critical Volumes of 

 Fluids," the suggestion was made that the critical pressure of 

 hydrogen was wrong, and that instead of being 99 atmospheres (as 

 deduced by Sarrau from Amagat's isothermals) the gas had probably 

 an abnormally low value for this constant. This view was sub- 

 stantially confirmed by Wroblewski finding the critical pressure of 

 13*3 atmospheres, or about one-fourth of that of oxygen. The 

 • Chemical News,' September 7, 1894, contains an account of the 

 stage the author's hydrogen experiments had reached at that date. 

 The object was to collect liquid hydrogen at its boiling point, in an 

 open vacuum vessel, which is a much more difficult problem than 

 seeing it in a glass tube under pressure and at a higher temperature. 

 In order to raise the critical point of hydrogen to about —210°, 

 from 2 to 5 per cent, of nitrogen or air was mixed with it. This is 

 simply making an artificial gas containing a large proportion of 

 hydrogen which is capable of liquefaction by the use of liquid air. 

 The results are summed up in the following extract from the paper : 

 " One thing can, however, be proved by the use of the gaseous 

 mixture of hydrogen and nitrogen, namely that by subjecting it to a 

 high compression at a temperature of —200° and expanding the 

 resulting liquid into air, a much lower temperature than anything 

 that has been recorded up to the present time can be reached. This 

 is proved by the fact that such a mixed gas gives, under the condi- 

 tions, a paste or jelly of solid nitrogen, evidently giving off hydrogen, 

 because the gas coming off burns fiercely. Even when hydrogen 

 containing only some 2 to 5 per cent, of air is similarly treated, the 

 result is a white solid matter (solid air) along with a clear liquid of 

 low density, which is so exceedingly volatile that no known device 

 for collecting it has been successful." This was in all probability the 

 first liquid hydrogen obtained, and the method is applicable to other 

 difficultly liquefactible gases. 



Continuing the investigations during the winter of 1894, and the 

 greater part of 1895, the author read a paper before the Chemical 

 Society in December of that year entitled, " The Liquefaction of Air 

 and Research at Low Temperatures," * in which occasion was taken to 

 describe for the first time the mode of production and use of a Liquid 

 Hydrogen Jet. At the same meeting Professor William Eamsay made 

 an announcement of a sensational character, which amounted to stating 

 that my hydrogen results had been not only anticipated but bettered. 

 The statement made to the Society by Professor Eamsay, reads as 



'Proceedings ' nf the Chemical Society, No 158, 1895. 



