1910] Light Reactions at Low Temperatures 021 



WEEKLY EVENING MEETING, 



Friday, Jaiiuaiy 21, 1910. 



Sir William Orookes, LL.D. D.Sc. For. Sec. Roy. vSoc. 

 Honorary Secretary and Vice-President, in the Chair. 



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

 Fullerian Professor of Chemistry. 



Light Reactions at Low Temperatures. 



[ABSTRACT.] 



The physiological action of light was the subject of my first Friday 

 Evening Lecture. At that time it almost seemed that we should not 

 materially add to our knowledge of physiological problems by the 

 application of very low temperatures. Later researches conducted in 

 conjunction with Professors McKendrick and Macfadyen established 

 that mere cooling did not destroy putrefying organisms, and also that 

 other bacilli were not destroyed by continued alternations of warmth 

 and extreme low temperatures. Seeds which had been kept for six 

 hours in liquid hydrogen suffered no loss of vitality, neither did 

 bacteria. It has been thought that chemical action is impossible 

 at the low temperatures now obtainable, but there are reactions 

 which are still possible. As an example your attention will be drawn, 

 among other things, to the results of some recent experiments on 

 phosphorescent bacteria, these organisms being peculiarly adapted for 

 investigations of this kind from their special property of producing 

 luminosity during life. 



In dealing with light reactions, care must be taken to exclude the 

 action of the radiant heat which always accompanies it. This involves 

 the need of some arrangement like a water cell built up with quartz 

 windows, which absorbs heat but is transparent to invisible light of 

 short wave-length. 



Experiments showing some effects of light radiation. — Here is a 

 tall glass jar containing some chlorine peroxide, a yellow gas mixed 

 with the air. When the radiation from the arc lamp is made to pass 

 through it, decomposition is at once evident from the clouds which 

 are formed. 



The change of colour by cooling which is shown by some substances 

 is of a different order. A strip of paper coated with red iodide of 

 mercury can be cooled by simply dipping half-way into liquid air. 

 The effect is to change the red to yellow in the cooled region. 



The fluorescent appearance of some bodies when exposed to light is 

 well known. This tall cylinder contains simply water, illuminated by 



