NEW RESEARCHES ON LIQUID AIR. 1 



By Professor Dewae, M. A., LL. D., F. R. S., M. R. I. 



Of all the forms of engineering plant used in low-teniperature 

 research, the best and most economical for the production of liquid air 

 or oxygen is one based on the general plan of the apparatus used by 

 Pictet in his celebrated experiments on the liquefaction of oxygen in 

 the year 1878. Instead of using Pictet's combined circuits of liquid 

 sulphur dioxide and carbon dioxide, maintained in continuous circula- 

 tion by means of compression, liquefaction, and subsequent evapora- 

 tion, it is preferable to select ethylene (after Cailletet and Wroblewski) 

 for one circuit, and for the other either nitrous oxide or, better, carbon 

 dioxide. Further, instead of making highly compressed oxygen to be 

 liquefied by heating potassium chlorate in an iron bomb directly con- 

 nected with the refrigerator, it is safer and more convenient to use gas 

 previously compressed in steel cylinders. The stopcock that Pictet 

 employed to draw off liquid and produce sudden expansion was in his 

 apparatus placed outside the refrigerator proper, but it is now placed 

 inside, so as to be kept cool by the gases undergoing expansion. This 

 improvement was introduced along with that of isolating the liquid 

 gases by surrounding them with their own cooled vapor in the appa- 

 ratus made wholly of copper, described and figured in the Proceedings 

 of the Royal Institution for 1886. In all continuously working circuits 

 of liquid gases used in refrigerating apparatus, the regenerative princi- 

 ple applied to cold, first introduced by Siemens in 1857, and subse- 

 quently employed in the freezing machines of Kirk, Coleman, Solvay, 

 Linde, and others, has been adopted. Quite independently, Prof. Kam- 

 erlingh Onnes, of Leyden, has used the regenerative principle in the 

 construction of the cooling circuits in his cryogenic laboratory. 2 Apart, 

 therefore, from important mechanical details and the conduct of the gen- 

 eral working, nothing new has been added by any investigator to the 

 principles involved in the construction and use of low- temperature appa- 

 ratus since the year 1878. Detailed drawings of the Royal Institution 



1 Eead at weekly evening meeting of Eoyal Institution of Great Britain, March 

 27, 1896, Edward Frankland, esq., D. C. L., LL. D., F. E. S., vice-president, in the 

 chair. Printed in Proceedings of the Institution, Vol. XV, Fehruary, 1897, page 133. 



2 See paper hy Dr. H. Kamerlingh Onnes on the " Cryogenic laboratory at Leiden, 

 and on the production of very low temperatures," Amsterdam Akademie, 1894. 



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