748 Prof. H. E. Armstrong on Low-Temperature Research 



The appearance was only manifest in the case of oxygen com- 

 pounds. In this lecture another striking demonstration was given 

 showing that ozone could be produced by heating oxygen to about 

 1600° in a platinum tube. A diagram of this apparatus also will be 

 found in the printed abstract. 



The inquiry was resumed at a later date (p. 41). 



The Liquefaction of Gases. 



Faraday's work on this subject ceased in the year 1845 ; he had 

 carried the inquiry as far as the knowledge of the time permitted. 

 It was not until "^ Andrews, in 1864, had studied the behaviour of 

 carbon dioxide under pressure at various temperatures and, as a con- 

 sequence, had introduced a new theoretical conception — that of the 

 critical temperature : the temperature above which liquefaction of a 

 gas could not be effected, whatever the pressure — that the direc- 

 tion was indicated in which progress could be made. Between the 

 close of 1877 and early in ls78, the scientific world learnt with the 

 greatest surprise that two independent workers, M. Cailletet, a French 

 ironmaster, and M. Pictet, a Swiss engineer, using very different 

 methods, had both succeeded, it was affirmed, in liquefying not only 

 oxygen but also hydrogen. The apparatus they used is figured and 

 described under " Hydrogen," in a short article the writer contributed 

 to the ninth edition of the " Encyclopedia Britannica " (vol. ix, 

 p. 433). 



On June 14, 1878, in a lecture on " The Liquefaction of G-ases," 

 Prof. Dewar gave a complete though condensed summary of the 

 work done up to that date on the subject. He then described the 

 remarkable achievements of MM. Cailletet and Pictet and gave 

 demonstrations of the method adopted by the former with apparatus 

 similar to that he had used : the method involved the sudden release 

 of the pressure on a small quantity of highly compressed, cooled gas, 

 liquefaction being due to the cooling caused by the sudden expansion * 

 it was rendered obvious through the momentary formation of a mist 

 in the tube. 



The lecture ends on a note of optimism which was only justified 

 after many years, very largely through work done in the Royal 

 Institution. " The work of Faraday has been completed ; every gas 

 may be forced to appear as a liquid." 



It is worth noting that the lecturer did not commit himself to 

 saying — has been but merely may he. It was soon realized that, 

 although correct as regards oxygen, Pictet's statement about hydrogen 

 could not be accepted and that, under the conditions he developed, the 

 liquefaction, let alone the solidification, of hydrogen was impossible. 

 It is now known that the solid spoken of as solid hydrogen, projected, 



