50 



T ran s^orf ions. 



of the kinetic theory is that this factor is very small — this dilution should 

 have little effect in reducing the number of collisions between aldehyde 

 molecules and oxygen atoms. It is known that in solution the effect of 

 some inert substance, as far as retarding the reaction is concerned, is very 

 slight, and the same probably holds in the gaseous state. The effect of 

 this factor, if at all noticeable, would be to reduce the value of K' as the 

 oxygen-pressure increased. 



These seem to be the only possible determining factors from the theo- 

 retical standpoint, and if, as Dr. Ewan found, the action goes on readily 

 with the oxygen-pressure at 450 mm., and ceases practically altogether 

 with the pressure at 550 mm., no theoretical explanation seems forthcom- 

 ing ; in fact, it is almost inconceivable that so sudden a break should occur. 



The Effect of Temperatuke on the Reaction. 



The effect of rise of temperature on the reaction is, as would be expected, 

 to increase the value of K'. At first increase of temperature by a few 

 degrees seems to have very little effect, but at 50° C. the aldehyde is 

 oxidized very rapidly, practically the whole being converted into acetic 

 acid in the course of a few hours. There can be no doubt that the degree 

 of dissociation of oxygen atoms becomes greater as the temperature rises, 

 and this, together with the increased speed of the molecules, would account 

 for the increased rate of oxidation. It was not considered necessary to 

 make experiments at a temperature higher than 50° C, as little further 

 would be illustrated, the speed at that temperature being sufficiently great 

 to measure accurately. In the first experiment' at 21° C. the proportion 

 of aldehyde is rather greater than in the other cases, giving perhaps a 

 higher value of K' than otiicrwise. 



Partial pressure of nitrogen = 20 mm. 

 Partial pressure of acetic acid= 12 mm. 



Partial pressure of nitrogen =17 mm. 

 Partial pressure of acetic acid = 15 ram. 



