﻿534 Dr. T. Ewan on the Rate of Oxidation 



dC 

 j- 1 is the rate at which the system AjBj . . . changes into 



the other system CjDj ... d is the concentration of the first 

 system, C A , C B ,&c.the concentrations of the substances A, B . . . 



In cases in which the numbers of molecules taking part in 

 a reaction are unknown, measurements of the velocity of the 

 reaction may be made use of for their determination. 



Applying this to the reaction between aldehyde and oxygen, 



we have — -—■ in equation 6 proportional to —~- in 



equation 5. C A we may put proportional to the pressure of 

 the aldehyde-vapour, and C B to the pressure of the oxygen 

 gas. Making these substitutions in 6, we get 



~~dt = coust 2>%'Pl 



and comparing this with 5, w r e see that m = l and n=^. The 

 reaction between aldehyde and oxygen may therefore be written 



C 2 H 4 + = C 2 H 4 2 . 

 We must suppose that the reaction consists in the addition of 

 an oxygen atom to a molecule of aldehyde. 



The assumption that a certain small number of oxygen atoms 

 exist normally in oxygen gas, is in accordance with our present 

 knowledge on the subject. Williamson was led by his studies 

 on the formation of ethers to propose the theory that the atoms 

 of which the molecules of a gas are composed frequently 

 change partners. For this to be possible, a certain number 

 of atoms must be at any moment in the act of transition, that 

 is free. The theory of Clausius, based on the phenomena of 

 electrolytic conductivity, and more recently that of Arrhenius, 

 supposes a similar condition to exist in solutions of electro- 

 lytes. In 1884 J. J. Thomson * developed a mathematical 

 theory of chemical reactions between gases, based on the ideas 

 of Williamson and Clausius ; the results are in agreement with 

 those obtained experimentally with aldehyde and oxygen. 



The probability of the existence of free atoms in oxygen 

 gas may be shown in another way. There can be little doubt, 

 from analogy, that the oxygen molecule would, at a sufficiently 

 high temperature, be dissociated into its atoms. Equilibrium 

 will be established when the concentration of the atoms has 

 reached a certain value which is determined by the equation 

 rj — kC, 2 



V (0 2 ) — /CU (0)J 



w T here C (0 } is the concentration of the oxygen molecules and 

 * Phil. Mag. [5] xviii. p. 233 (1884). 



