1894.) Professor Deivar on Scientific Uses of Liquid Air. 393 



WEEKLY EVENING MEETING, 

 Friday, January 19, 1894. 



Sir Frederick Bramwell, Bart. D.C.L. LL.D. F.R.S. 

 Honorary Secretary and Vice-President, in the Chair. 



Professor Dewar, M.A. LL.D. F.R.S. M.B.I. 



Scientific Uses of Liquid Air. 



When Faraday was working on liquid gases in this Institution 

 about 1823, with such means as were then at his command, his 

 inquiry was limited to the determination of the specific gravities 

 and vapour pressures of such bodies. Twenty years later, by the 

 use of solid carbonic acid, the greatest cold then possible was 

 obtained, and Faraday made admirable use of Thilorier's new 

 cooling agent to extend his early investigations. Just as liquid 

 carbonic acid produced in glass tubes was of no use as an agent for 

 effecting the liquefaction of more resisting gaseous matters, until it 

 could be manipulated in the solid state, so liquid air, until it could 

 be handled, stored and used in open vessels, like any ordinary liquid, 

 could not be said to possess scientific uses in any wide sense. Such 

 operations become easy when double-walled vacuum vessels (such 

 as were described in a former lecture) are employed in the conduct 

 of experiments where substances boiling at very low temperatures 

 have to be manipulated. The chief scientific use of liquid air 

 consists in the facilities it gives for the study of the properties of 

 matter at temperatures approaching the zero of absolute temperature. 

 In this lecture the expression liquid air may mean either oxygen or 

 air. Where a constant temperature is required oxygen is used. 

 Liquid air made on the large scale may contain, after it is collected 

 in open vacuum vessels, as much as 50 per cent, of oxygen. Such 

 a liquid boils between — 192° and — 182° C, and the longer it is 

 stored the nearer it comes to — 182° C. or the boiling point of pure 

 oxygen. For a number of experiments of a qualitative character, 

 whether it is liquid air or oxygen that is used makes no difference. 

 In many of the experiments to be recorded, liquid oxygen made 

 from the evaporation of liquid air was employed. In pursuing 

 this subject in consort with Professor Fleming,* a long series of 

 experiments, involving the use of large supplies of liquid oxygen, have 

 been carried out on the electric resistance of metals and alloys, and 



* ' The Electrical Resistance of Metals and Alloys at Temperatures Approach- 

 ing the Absolute Zero.' By James Dewar, LL.D. F.R.S. and J. A. Fleming, 

 M.A. D.Sc. F.R.S. Professor of Electrical Engineering in University College, 

 London, Phil. Mas. 1892. 



