ON ARTIFICIAL REFRIGERATION. 921 



liquid was seen on the surface of the quicksilver, in quantity about rr;^,fjj 

 part of the volume of air. The gasometer was at another time charged 

 witii carburetted lijdrogen," and "it was subjected to diflerent pressures, 

 and it began to liquefy at about 40 atmospheres, and at 1,200 atmos- 

 pheres the whole was liquetied." 



"These instances of apparent condensation of gaseous fluids were first 

 observed in January, 182li; but for want of chemical knowledge requisite 

 to ascertain the exact nature of the liquids produced, I did not pursue 

 the inquiry further; and as the subject has been taken up by those who 

 are eminently qualified for the investigation, I need not regret my ina- 

 bility to make full advantage of the power I had the means of api)lying." 



Jacob Perkins knew probably more than any of his contemporaries 

 as to the means whereby an apparatus could be constructed to stand 

 such pressures. lie aftervv'ards invented the steam-gun, and no doubt 

 his Ivuowledgo of the liquefaction of gases led him directly to the recon- 

 densation of the ether vapor in the ice-machine patented, a drawing of 

 Avliich is appended to this paper. Sir Humphrey Davy appeared in no 

 admirable light on this question in relation to Faraday. He was presi- 

 dent of the Eoyal Society in 1823, and in this year he asked his pupil 

 and assistant to liquefy chlorine. Can Perkins's important paper, draw- 

 ings and all, have been lost by mere accident ? Dr. Andrews has i^ointed 

 out that to determine the certainty of the liquid and solid state of matter 

 is a much more difticult subject for experiment than the relation between 

 gases and liquids. In this relation Mr. Perkins's observations of the 

 crystalization of acetic acid under i^ressure is at all events interesting. 



However this may be, we may repeat in Mr. Wurtz's words that " the 

 experiments of MM. Raoul Pictet and Cailletet have removed from 

 science the distinction between i)ermanent and condensable gases." 

 Cailletet liquefied oxygen and carbonic oxide on the 2d of December, 

 1877. Being a candidate for election to a seat in the Academy of 

 Sciences he delayed the announcement, after having consigned a state- 

 ment of the discovery to a sealed packet, till the session of the 24th of 

 December. At the same time Raoul Pictet's results by low temperature 

 produced with the combined aid of sulphurous and carbonic acid gases 

 were i)ublished, and confirmed Cailletet's exijeriments in which lique- 

 faction lias been induced by "detente" or expansion of the gas compressed 

 at low temperature. On the last day of 1877 Cailletet liquefied hydrogen, 

 nitrogen, and atmospheric air, and on the 11th of January ^I. Pictet 

 solidified hydrogen, proving it to be a metal, as previously supposed by 

 Professor Dumas. 



This suspicion had been almost transformed into certainty by the ad- 

 mirable work of Graham, in foruiing hycbMjgenium alloys — notably with 

 palladium : and while palladium itself was known to be capable of but 

 feeble magnetism, its hydrogenium alloy was found to become strongly 

 magnetic. 



Space forbids that I should prolong this history, but it is important 



