240 Professor Sir James Dewar [Jan. 2a, 



WEEKLY EVENING MEETING, 



Friday, January 23, 1014. 



Sir James Crichtox-Browxe, J. P. M.D. LL.D. D.Sc. F.R.S., 

 Treasurer and Vice-President, in the Chair. 



Professor Sir James Deavar, LL.D. D.Sc. F.R.S. JI.R.I., 

 Fullerian Professor of Chemistry, R.I. 



The Coming of Age of the "Vacuum Flask." 



Twenty-one years ago the.appHcation of vacuum jacketed vessels to 

 the storage and manipulation of liquefied gases or for conserving hot 

 liquids was made in the Laboratory of the Royal Institution. Such 

 vessels are now popularly called " Thermos Flasks." The insulating 

 properties of a vacuum in preventing the influx of heat by the elimina- 

 tion of convection currents had been known to physicists ever since 

 the investigations of D along and Petit on the laws of radiation, in the 

 early part of the last century, proved the important part played by 

 the gas particles surrounding a body in dissipating heat, otherwise 

 than by pure radiation . As far back as 1 8 7 3 a highly exhausted annular 

 metallic vessel was used by the lecturer in calorimetric experiments 

 described in my paper on " The Physical Constants of Hydrogenium." * 

 This naturally suggested that the use of high vacua in the annular space 

 surrounding vessels containing liquid gases would be advantageous. 

 The experiments which led up to the use of glass vessels isolated by 

 a vacuum space are fully described in the Friday Evening Discourse 

 on January 20, 1 893.1 Some of the early forms of vessels then 

 described are shown in Fig. 1. 



One of the primary difficulties was connected with the construc- 

 tion in glass of concentric spherical or cylindrical vessels that would 

 withstand the atmospheric pressure, and Ijear considerable oscillations 

 of temperature without cracking. This was a serious impediment 

 which was only gradually overcome by the growing demand and by 

 improvements in the blowing and adequate annealing of the glass : 

 some of the various developments of form rising out of the needs 

 of low^ temperature research are figured in the abstract of the 

 Discourse of January 18, 1001, which is now reproduced. 



A sufficient vacuum can be obtained with the ordinary Sprengel 

 pump. Glass flasks so exhausted were quite satisfactory for heat 



* Trans. Roy. Soc. Ed. xxvii. p. 167. 

 t Proc. Roy. Inst., xiv. p. 1. 



