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



and more especially that scientific men could be got to give them any 

 currency in this country." 



On this occasion, a small-scale laboratory apparatus for the lique- 

 faction of oxygen and other gases was exhibited and explained. The 

 value of vacuum vessels was also demonstrated and made obvious to 

 all by means of a calorimeter consisting of three similar vacuum 

 tubes joined to a common stem ; in one of these the annular space 

 contained air ; in the other vessels it was exhausted but the walls of 

 one were silvered in addition ; ethylene was liquefied in each of the 

 inner tubes and the rate at which evaporation took place in each 

 tube was indicated by the height of the flame given when the escaping 

 gas was fired at a tube inserted into the mouth of the vessel. 



A variety of interesting demonstrations were given on this occa- 

 sion, one being of the method of ascertaining the density of liquid 

 oxygen and of liquid air by weighing various substances in the liquid. 

 Probably the most significant was that showing that the gas nitric 

 oxide might be condensed to a nearly white sohd which became a 

 blue liquid when melted, the colour being more pronounced at the 

 melting than at the l)oiling-point, a fact which might be regarded as 

 evidence that the gas had been entirely deprived of the higher 

 oxide. The observation is of importance as an indication that, at 

 low temperatures, the simple molecule NO — one of the most enig- 

 matical compounds known to the chemist — is capable of combining 

 with itself. It may be surmised that perhaps three such simple 

 molecules are associated in the coloured liquid. 



On this occasion, one of Prof. Dewar's most fascinating demon- 

 strations wa« first displayed — that of burning a jet of hydrogen 

 below the surface of liquid oxygen ; graphite and diamond were also 

 burnt in this way in face of the audience. The demonstrations were 

 striking, not only as instances of daring and of dexterous manipu- 

 lation but also on account of the proof that was given of the 

 formation of ozone, under such conditions, by the gradual conversion 

 of the colourless solvent into a blue liquid, owing, to the condensation 

 of the ozone and its dissolution in the liquid oxygen. It must be 

 supposed that in all cases of combustion in oxygen, the molecule of 

 the gas undergoes dissociation, thus : — 



+ -h ^ Oo. 



It is permissible to lay stress on the fact that such observations 

 do not really prove that chemical action may take place at the 

 lowest temperature, nor that their occurrence is independent of the 

 presence of a third factor ; directly the hot body is introduced into 

 the liquid it must create its own atmosphere and within this every 

 grade of temperature may prevail. 



The report of the lecture contains the all-significant statement : 



