258 



Sir James Dewar 



[Jan. 20, 



the vacuum vessel E. In a short time a ring of blue liquid begins to 

 form in the tube a little above the level of the liquid air. This is 

 condensed liquid ozone, which quickly dissolves when brought into 

 contact with the liquid ah-. 



The rapid oxidation of silver, as shown by the blackening of the 

 metal which results from the action of ozone on a plate of polished 

 silver at ordinary temperature, is well known ; if, however, a strip of 

 silver G (Fig. 1) be cooled in liquid air and placed in the tube F 

 connected to the ozoniser C and subjected to the action of the 

 gaseous ozone, no blackening is noticed for a considerable time, but as 



soon as it warms up to the 

 temperature of the room the 

 strip turns black. If a similar 

 piece of silver be immersed 

 in liquid air containing ozone 

 in solution, and left there in- 

 definitely, there is no apparent 

 action and no blackening 

 results. 



From the early days of 

 low temperature research it 

 has been known that mere 

 cooling to the temperature of 

 liquid air does not destroy 

 bacterial life, the organisms 

 recovering their vital func- 

 tions after weeks of immer- 

 sion. The bactericidal effect 

 of the ultra-violet light was 

 discussed in the Friday 

 Evening Discourse, 1910, on 

 Light Reactions at Low 

 Temperatures,* when it was 

 shown that the eifect of the 

 ultra-violet light on bacteria, 

 even at the temperature of 

 liquid air, was to pulverize 

 the organisms. It has been found by experiment that the bacteria 

 can be protected from the action of the ultra-violet light by means of 

 thin sheet lead. Aluminium foil, on the other hand, is sufficiently 

 transparent for the ultra-violet rays to remain effective in killing the 

 bacteria. 



Bacteria cooled in liquid air may also be subjected to the action 

 of the cathode discharge in the following way. A glass tube A 

 (Fig. 2), provided with platinum electrodes B and C, is connected 



* Proc. Roy. Inst., vol. XIX., p. 921. 



Fig. 



