Mr Bevan, A Method of following the Course, etc. 269 



A method of following the course of certain chemical actions, 

 and a period of induction in the action of excess of water on 

 monochloracetic acid. By P. V. Bevan, M.A., Trinity College. 



[Read 12 March 1906.] 



The experiments which are described in this paper arose from 

 an endeavour to trace the initial course of the action of water on 

 monochloracetic acid, with a view to testing the theory that, in 

 actions of this type where a double decomposition takes place, the 

 first stage of the action is an association of the two reacting 

 molecules. In certain other chemical actions, especially the union 

 of hydrogen and chlorine, an induction period, a period during 

 which the action does not go on with the maximum velocity under 

 the conditions of the experiment, is observed. This induction 

 period admits of explanation if we assume that the first stages of 

 the action consist in a union between the reacting molecules, or 

 of these with other molecules, to form a molecular aggregate, 

 in which the individual atoms can come into each other's spheres 

 of action. The action then would go on by a breaking down of 

 these aggregates giving rise to the final products. 



It is difficult to form a picture of the process of such actions, 

 unless something of this kind takes place, as for example in the 

 case of hydrogen and chlorine when we have the two perfectly 

 stable systems which in a pure state shew practically no tendency 

 to combine even under the influence of light. And in such an 

 action as that of monochloracetic acid and water it seems probable 

 that, for a pair of molecules to react, they should first get into 

 some more intimate relation than that simply of a dissolved 

 molecule and molecule of solvent. The action takes place accord- 

 ing to the equation 



CH 2 ClCOOH + H 2 = CH 2 . OH . COOH + HC1, 



glycollic acid and hydrochloric acid being formed. This action 

 has been studied*, and it has been found to follow the normal 



* Buchanan, Berichte, iv. 340, 1871. Van 't Hoff, Studies in Chemical 

 Dynamics, p. 14. 



