56 



NATURE 



[May 19, 1898 



All this is typical of British methods. The members 

 of a great private Institution have secured the services of 

 a man in whose abilities they believe. They supply him 

 freely with the sinews of war, and he justifies their con- 

 fidence by achieving a success which, as far as our present 

 knowledge goes, could only have been won by a combin- 

 ation of great resources and very great skill. We heartily 

 congratulate Prof. Dewar and his supporters on this 

 result, and on the fact that the world now possesses liquid 

 hydrogen — so to speak — on tap. 



The conditions of the experiment give some idea of 

 the difficulties which have been overcome. Hydrogen 

 cooled to - 205' C. escaped, under a pressure of 180 atmo- 

 spheres, into a vacuum vessel surrounded by a space 

 which was itself maintained at a temperature of - 2oo~ C. 

 Thus constrained it liquefied. 



About 20 c.c. of the liquid were collected in another 

 protected vessel, into which it dripped from that above 

 described. It is transparent, colourless, with a well- 

 defined meniscus, and apparently with a relatively high 

 refractive index. 



We sincerely hope that this great success will not be 

 marred by a controversy as to priority, of which some 

 symptoms have already appeared in a leading article in 

 the Standard and elsewhere. The time is long past 

 in which the liquefaction of a gas was interesting as 

 proving that under proper conditions all substances can 

 be liquefied. For many years nobody has had doubts 

 on that point. We have learned to look upon the 

 liquefaction of a gas as important, mainly because it 

 affords a means of studying at very low temperatures 

 not only the liquefied gas itself, but also other kinds of 

 matter. Experiments in which momentary liquefaction 

 is attained are chiefly ^interesting as showing that some 

 approach is made to realising the condition under which 

 more stable results may be expected. They take a much 

 higher rank if the skilful experimenter can wrest from the 

 substance in a transitory condition some information as 

 to the properties which the material would have if it 

 were reduced to the state which has been called a 

 " static liquid." To attain these results in the case of so 

 intractable a substance as hydrogen is an achievement 

 of a very high order. But when this has been done it 

 cannot be fairly contended that all the rest follows as a 

 matter of course. 



There have been discoveries in which the first step 

 was all-important. The discovery, for instance, of the 

 Rontgen rays opened an entirely new range of facts 

 to scientific investigation. In other cases the root-idea 

 had long been common property, and the merit, like 

 that of Captain Bunsby's observation, " lays in the 

 application of it." It has long been known that if 

 hydrogen were ever liquefied inquantity, both cooling to a 

 very low temperature, and a rapid expansion would play 

 a large part in the operation. The difficulties of the 

 experiment lay, not in understanding these principles, but 

 in applying them, and the difficulties were so enormons 

 that the investigator who has overcome them deserves 

 our admiration. He has performed not only a great 

 " tour de force," but has cleared the way to a region 

 hitherto unexplored, to a whole series of researches 

 which become more interesting and important as the 

 absolute zero is more nearly approached. 



It appears to us, therefore, that there is no necessity 

 to belittle the work either of Prof. Dewar or of others 

 who have been active in the same line of research. 

 Cailletet and Wroblewski obtained results which, to judge 

 from his address to the French Academy, reported in 

 the Times o{ May 17, are regarded as inconclusive by 

 so high an authority as M. Moissan. At the best, and 

 assuming the liquid obtained to have been hydrogen, 

 its existence in the liquid form was very brief. Prof. 

 Olszewski also ha ; published a full account of how he 

 obtained hydrogen for a moment in a mist-like state, in 



NO. 1490, VOL. 58] 



which he measured some of the constants of the liquid. 

 Yet nothing but the paucity of language could lead to 

 the idea that this feat was the same as that which Prof. 

 Dewar has accomplished. Had we no other evidence 

 of the existence of water, something might be learned 

 from the study of clouds ; but nobody contends, on that 

 ground, that a cloud is the same thing as a duck-pond. 

 Yet the difference between the two is hardly, if at all, 

 greater than the practical difference between hydrogen 

 without visible form or surface, in a state of momentary 

 or "dynamical" liquefaction, and hydrogen as a "static '" 

 liquid, with a clearly defined meniscus, boiling away 

 quietly under conditions which enable the observer to 

 record its appearance, to handle and to use it. 



By insisting on this difference, we do not for a moment 

 wish to cjuestion the merits of Prof. Olszewski's work. 

 He used the means at his disposal admirably, and m ide 

 measurements of the critical temperature and boiling- 

 point of hydrogen, which, tested as they were by check 

 experiments on oxygen and ethylene, were of great value. 



Prof. Olszewski was, however, fully conscious of the 

 difference between these results and those which Prof. 

 Dewar has now achieved. He again and again explained 

 with the utmost candour that he had seen no meniscus, 

 and that he had failed to reduce hydrogen to the state 

 of a " static liquid." He further expressed the opinion 

 that these desiderata would not be attained until a cooling 

 agent was discovered in the form of a gas, with a density 

 between those of hydrogen and nitrogen. No such gas 

 has been used by Prof. Dewar, yet hydrogen has now 

 been seen by himself, by Lord Rayleigh and others as a 

 well-defined liquid mass. The merits of this achievement 

 will be in no wise diminished by a generous recognition 

 of the researches of Olszewski, but on the other hand it 

 would be most unfair to minimise the magnitude of 

 Prof. Dewar's success by classing it merely as a repetition, 

 on a larger scale, of another man's work. It is in the 

 words of M. Moissan a " wonder of modern chemistry." 



The following abstract of the paper will give further 

 details : — 



In a paper entitled " The Liquefaction of Air and Research 

 at Low Temperatures,'" read before the Chemical Society, and 

 published in the Proceedings, No. 158, an account is fjiven of the 

 history of the hydrogen problem and the result of my own expe- 

 riments up to the end of the year 1895. The subject is again 

 discussed in a Friday evening lecture on " New Researches on 

 Liquid Air" {l\oy. Inst. Proc, 1896), which contains a drawing 

 of the apparatus employed for the production of a jet of hydrogen 

 containing liquid. It was shown that such a jet could be used 

 to cool bodies below the temperature that could be reached by 

 the use of liquid air, but all attempts to collect the liquid ir> 

 vacuum vessels failed. No other investigator has so far im- 

 proved on the results described in 1895. The type of apparatus 

 used in these experiments worked well, so it was resolved to 

 construct a much larger liquid air plant, and to combine with it 

 circuits and arrangements for the liquefaction of hydrogen, which 

 will be described in a subsequent paper. This apparatus, ad- 

 mirably constructed by the engineers, Messrs. Lennox, 

 Reynolds, and Fyfe, took a year to build up, and many 

 months have been occupied in testing and making preliminary 

 trials. The many failures and defeats need not be detailed. 



On May 10, starting with hydrogen cooled to -aos^C, and 

 under a pressure of 180 atmospheres, escaping continuously from 

 the nozzle of a coil of pipe at the rate of about 10 cubic feet to 

 15 cubic feet per minute, in a vacuum vessel double silvered and 

 of special construction, all surrounded with a space kept below 

 - 200" C. Liquid hydrogen commenced to drop from this 

 vacuum vessel into another doubly isolated by being surrounded 

 with a third vacuum vessel. In about five minutes, 20 c.c. of 

 liquid hydrogen were collected, when the hydrogen jet froze up 

 from the solidification of air in the pipes. The yield of liquid 

 was about i per cent, of the gas. The hydrogen in the liquid 

 condition is clear and colourless, showing no absorption spec- 

 trum, and the meniscus is as well defined as in the case of liquid 

 air. The liquid must have a relatively high refractive index and 



