702 Miss Agnes M. Clerhe 



gaseous blend, subjected to powerful pressure at a temperature of 

 - 200° C, and then permitted to expand, gave rise to a degree of cold 

 below any previously attained, and there resulted a deposit of solid 

 air, together with a clear liquid of small density, too volatile for 

 collection by any available device. This was, doubtless, the first 

 sample of genuinely liquefied hydrogen ever exhibited to view. 



Professor Dewar's object, however, was not merely to catch sight 

 of liquid hydrogen, but to get hold of it. Enclosed in a glass tube, 

 under pressure, it still remained comparatively inaccessible. Until 

 it could be made to accumulate, at its boiling-point, in open vacuum- 

 vessels, no satisfactory study of its nature was feasible. This goal 

 was finally reached through the introduction of the regenerating 

 coil. The principle of self-intensification had been, in 1857, applied 

 by Siemens to the production of cold. In subsequent years its 

 efficacy in this direction was turned to account for industrial pur- 

 poses by Coleman, Solvay, Linde and others ; while Dr. Kamerlingh 

 Onnes had recourse to it in his cryogenic laboratory at Leiden in 

 1894. The prompt and copious liquefaction of refractory gases 

 thus became an ordinary operation ; but it was only at the Royal 

 Institution that the facilities secured wore made to serve for largely 

 widening the scope of research. 



In December 1895, Professor Dewar read a paper before the 

 Chemical Society describing the mode of production and use of a 

 liquid hydrogen jet. Owing to the rapid movement of the con- 

 densing gas, and the low specific gravity of the resultant liquid, 

 attempts to collect it were fruitless ; but, with better isolation aud 

 more perfectly adapted vacuum-tubes, their future success was antici- 

 pated. Meanwhile, research at some 20° or 30° above absolute zero 

 was already practicable, by using a liquid-hydrogen spray as a 

 cooling agent. Financial difficulties alone stood in the way, and 

 they were not allowed wholly to bar progress. The type of re- 

 generative apparatus employed in 1895 being satisfactory, it was 

 resolved to develop it on a greatly enlarged scale in a liquid-air 

 plant, combining special arrangements for dealing with hydrogen. 

 Its construction took a year, and many months were occupied in 

 testing its capabilities. That they were of the high order required 

 to compel the unconditional surrender of the gas, was at last visibly 

 attested by the dropping of the condensed fluid into a triply-coated 

 vacuum-vessel, May 10, 1898. By a certain dramatic fitness, the 

 first display before an audience of this, so to speak, preternatural 

 substance was at Professor Dewar's lecture in commemoration of the 

 Centenary of the Royal Institution, June 7, 1899. A spheroidal 

 vessel, silvered and vacuum-protected, containing one litre of liquid 

 hydrogen, stood on the table, immersed in a bath of liquid air, for 

 the savants of two continents to see. With these precautions, 

 evaporation from it was not inconveniently rapid. The removal, 

 however, of a plug of cotton-wool from the mouth of the receptacle 

 caused an immediate deposition of air-snow; and the clogging of 



