HISTOEY OF COLD AND THE ABSOLUTE ZEEO. 219 



than li([iiid hydrogen, yet by a study of its isotherinals at low tein])er 

 aturc we shall succeed in tinding- its most important Tuiuid constants, 

 althoui^h the isolation of the real liquid may for tlu^ time he impossible. 

 It is perhaps not too much to say that as a prolitic source of knowledg-e 

 in the department dealini>- with the continuity of state in matter, it 

 would be necessary to go l)ack to Carnot's c^'^cle to find a proposition 

 of greater importance thaji the theory of van der Waals and his devel- 

 opment of the law of corresponding states. 



It will be apparent from what has just been said that, thanks to th(^ 

 labors of Andrews, van der Waals, and others, theory had again far 

 outrun experiment. We could calculate the constants and predict 

 some of the simple physical characteristics of liquid oxygen, hydrogen, 

 or nitrogen with a high degree of confidence long before any one of 

 the three had been obtained in the static liquid condition permitting of 

 the experimental verification of the theory. This was the more tanta- 

 lizing, because, with whatever confidence the chemist may anticipate 

 the substantial corroboration of his theory, he also anticipates with 

 almost e(|ual conviction that as he ap])roaches more and more nearly to 

 the zero of absolute temperature he will encounter phenomena com- 

 pelling modification, revision, and refinement of formulas which fairly 

 covered the facts previously known. Just as nearh^ sev^enty years ago 

 chenusts were waiting for some means of getting a temperature of 100-' 

 below melting ice, so ten years ago they wei'e casting about for the 

 means of going 100'- lower still. The difficulty, it need hardly l)e said, 

 increases in a geometrical rather than in an arithmetical ratio. Its 

 magnitude ma}^ be estimated from the fact that to produce liquid air 

 in the atmosphere of an ordinary laborator}^ is a feat analogous to the 

 production of licjuid water starting from steam at a white heat and 

 working with all the implements and surroundings at the same high 

 temperature. The problem was not so much liow to produce intense 

 cold as how to save it when produced from being immediately leveled 

 up by the relativel}' superheated surroundings. Ordinary nonconduct- 

 ing packings were inadmissible because they are both cumbrous and 

 o})aque, while in working near the limits of our resources it is essential 

 that th(» product should be visible and readily handled. It was while 

 puzzling over this mechanical and manipulatiNe difficulty in 18*J2 that it 

 occurred to me that the principle of an arrangement used nearly twenty 

 years before in some calorimetric experiments." which was based upon 

 the work of Dulong and Petit on radiation, might be employed with 

 advantage as well to protect cold substances from heat as hot ones from 

 rapid cooling. I therefore tried the efi'ect of keeping liquefied gases in 

 vessels having a double wall, the annular space between l)eing very 

 highly exhausted.'' Experiments showed that liquid air evaporated at 



""On the physical constants of hydrogenniin," Trans. Roy. Soc, ed. 187;!. 

 '' It now appears that similar vessels were employed by Professor V^ioUe uia researcli 

 entitled "Sur un calorimetre par refroidissement," Comp. Rendu, 1882. 



