256 Sir James Detcnr [Jan. 20, 



WEEKLY EVENING MEETING, 



Friday, January 20, 1911. 



His Grace the Duke of Northi^aiberlaxd, K.G. D.C.L. F.R.S., 

 President, in the Chair. 



Professor Sir James Dewar. M.A. LL.D. D.Sc. F.R.S. M.R.I., 

 Fullerian Professor of Chemistry. 



Chemical and Phi/siral Change at Low Temperatures. 



The retarding effect of extremely low temperatures on chemical 

 action has long been known, and it was generally supposed that at a 

 sufficiently low temperature all such action would be completely 

 suspended. This inference was much shaken • when it was found 

 that liquid hydrogen and solid fluorine combined with explosive 

 violence at 20° absolute.* One of the most characteristic reactions of 

 ozone is that it can be dissolved in carbon disulphide at a tempera- 

 ture of about —100° C, showing a deep blue colour, whereas on 

 slightly raising the temperature the colour disappears owing to rapid 

 oxidation. But perhaps the most remarkable of all low temperature 

 reactions is the fact mentioned in the Friday Evening Discourse, 1910,t 

 that soHd oxygen at the temperature of boiling hydrogen is capable 

 of being partially transformed into ozone by the impact of ultra-violet 

 rays. In this case the action is clearly a molecular transition, involv- 

 ing the absorption of energy, taking place in the solid state in one 

 body, and not an interaction of two bodies as in the cases of ozone 

 and carbon disulphide, and the combination of liquid hydrogen and 

 soUd fluorine. 



Action of Ozone at the Temperature of Liquid Air. 



A convenient method of illustrating the effects of low tempera- 

 tures on chemical action is by the use of liquid and gaseous ozone. 

 For the purpose of experiment its condensation can be easily effected 

 with the aid of liquid air, in the following manner. Oxygen, after 

 cleaning by passing through a U-tube B (Fig. 1) immersed in liquid 

 oxygen, is exposed to the silent electric discharge in the ozoniser C, and 

 bubbled through the tube D, the end of which dips into Uquid air in 



* Moissan and Dewar, Comptes Rendus, vol. CXXXVI. p. 643. 

 t Proc. Roy. lust., vol. XIX. p. 925. 



