344 HISTORY OF CHEMISTRY. [LECTURE XVI. 



temperatures by determining the potential of thermo-electric 

 currents, which is now largely employed, also originated with 

 them. 57 In the experiments that have been carried out latterly, 

 however, on the liquefaction of air and of other gases, Pictet's 

 method has been abandoned again, and recourse has been 

 taken to that of Cailletet (the latter method having been con- 

 verted into a dynamical or continuous one) ; that is to say, the 

 expansion of highly compressed gases has been employed in 

 order that the necessary lowering of temperature may be 

 effected. Thus Dewar, 58 in his experiments upon the produc- 

 tion of liquid air, liquefied, by its own expansion, air which was 

 under a pressure of 100 atmospheres and was cooled by solid 

 carbonic anhydride ; whereas the recent technical method con- 

 sists in cooling exclusively by expansion, and the effect of the 

 latter is turned to account in a very ingenious manner by the 

 employment of a self-intensive apparatus. Linde 59 in Germany, 

 and Hampson 60 in England almost at the same time con- 

 structed technically efficient forms of apparatus, based upon 

 this method, for the production of liquid air. 



Liquid air has not as yet, however, found any technical 

 application upon the large scale. Nearly pure oxygen is ob- 

 tained from it very cheaply, and the attempt has been made to 

 apply it in the technology of explosives, or to the production 

 of high temperatures, but no ultimate pronouncement can be 

 made with respect to this. Of far greater importance are the 

 results that liquid air has achieved in scientific investigation, 



In the first place, it must be mentioned that Dewar, by its 

 aid, has succeeded in liquefying helium, 01 and in obtaining air, 

 oxygen, and hydrogen in the solid state ; and that in doing so 

 he has achieved almost everything that can be done in this 

 direction. Dewar is at present engaged in trying to reach still 



57 Compare Holborn and Wien, Wiedem. Ann. 59, 220 ; and Lad en burg 

 and Kriigel, Berichte, 32, 1818. r>8 Journ. Royal Institution, 1878 ; 



1883-1885; 1892-1899. 59 Z. d. Vereines deutscher Ingenieure, 39, 1157. 

 60 British Patent, April 1896. 61 The Times, nth May 1898; Phil. 



Mag. [5] 45, 543 ; Comptes Rendus. 126, 1408 ; Ann. Chim. [7] 14, 145 ; 

 Proc. Chem. Soc. 14, 129, 146. 



