1911] 0)1 Chemical Change at Low Temperatures. 261) 



In both cases the brown solid was formed in the U-tube, but the 

 quantity obtained was less than under the ordinary conditions of 

 temperature. 



In none of the experiments was the amount of brown solid obtained 

 greater than in those in which the vapour from carbon disulphide at 

 - 78'' C. was passed through an ozoniser, and these conditions were 

 therefore adopted for all subsequent experiments. 



The determination of the ratio between the amounts of brown 

 solid formed in the U-tube and of carbon disulphide passed through 

 the ozoniser was found to be difficult owing to the almost invariable 

 breaking of the tube during the transformation. 



The ratio of the weight of the solid to that of the carbon disulphide 

 varied from 1 to 10 to 1 to 50 in different experiments, and was found 

 to depend on the form of the apparatus and the amount of solid sur- 

 face over which the ozoniser product passed. Another very potent 

 influence was found to be the deposit on the ozoniser surface. A 

 clean ozoniser gave a much larger quantity of brown solid than an 

 ozoniser that was coated with a deposit. 



The Transformation of the Condensed Ozoniser Product 

 INTO A Non-Volatile Solid. 



II The solid deposited in the condenser at - 185" C. is at first 

 white, but soon acquires a broAvn colour, the darkest portion being 

 nearest the liquid air surface. On allowing the temperature to rise, 

 the brown colour spreads rapidly, and this change is usually accom- 

 panied by a glow or flash and a detonation which may be violent 

 enough to shatter the condenser. The transformation may, however, 

 take place quietly without an audible detonation or a visible flash, 

 and, on the other hand, a detonation may take place while the con- 

 denser is still immersed in liquid air. 



The interposition of a cotton-wool filter between the ozoniser and 

 the condenser diminishes the intensity of the phenomena observed in 

 the condenser to a very considerable extent, and at the same time 

 increases the rate at which the brown solid is deposited in the ozoniser 

 and leading tubes. 



Quantitative experiment showed that the interposition of cotton- 

 wool filters reduced the rate of flow of carbon disulphide to about 

 one-fourth its former value, and the amount of brown solid to about 

 one-fifteenth. 



When the U-tube was replaced by a condenser of the test-tube 

 form cooled to —210° C. by immersion in liquid air under exhaustion 

 and the gases admitted, the solid deposit which was formed on the 

 bottom of the wide tube was perfectly white. After 15 minutes, 

 however, the deposit had acquired a brown colour, showing that even at 

 - 210° C. the transformation was taking place slowly. On allowing the 

 temperature to rise to - 185° C. the transition took place more rapidly. 



