480 UNIVERSITY OF VIRGINIA PUBLICATIONS 



In 1905 Brunner worked with zinc in solutions of hydrochloric acid, and 

 also in iodine solutions (11). This work, while on the whole confirming 

 the theory of reaction velocity given above, is very far from satisfactory. 

 The most systematic and definite work thus far done along this fine was 

 done by Van Name and Edgar in 1910. 



Work of Van Name and Edgar. In 1910 R. G. Van Name and Graham 

 Edgar undertook a series of experiments for the purpose of determining 

 more exactly reaction velocities between metals and dissolved halides 

 for the purpose of testing the validity of the diffusion theory of reaction 

 velocity. Having a very definite end in view Van Name and Edgar took 

 all possible precautions against such sources of error as were likely to 

 invahdate in any way their work for the particular end in view. All of 

 their work was done at the temperature of 45°; the stirring was thoroughly 

 and uniformly accomphshed by means of an eighth horse power motor. 

 Samples of iodine solution were withdrawn at desired intervals and titrated. 

 The velocity constant k could be determined as many times as desired 

 from the same materials. The following from Van Name and Edgar will 

 make clear the method of calculation (12). 



From the point of view of the diffusion theory the mechanism of the reaction 

 is as follows: the weight of iodine which reaches and reacts with the surface of the 

 metal in the time interval dt is the amount which can diiJuse through the adherent 

 layer of liquid in that time, that is according to Fick's law, it is proportional to the 

 concentration fall across the layer. Owing to the rapidity of chemical reaction the 

 concentration of the iodine at the surface of the metal is always practically zero. 

 At the outer surface of the layer it is equal to c, the concentration of the main solu- 

 tion. Hence the concentration fall is c, and if m is the total weight of available 

 halogen in the solution, 



dm _ d (co) _ 

 ~1t di ■ 



where K is the velocity constant. Integration for constant volume gives 



Van Name and Edgar worked with Hg, Cu, Zn, and Ag. Though 

 most of their work was done in iodine solution, some was also done in 

 bromine solution. Some attention was paid to the effects of stirring at 

 different rates, and to temperature effects. 



As was to be expected the rate of reaction was increased in all cases 

 by increasing the rate of stirring. This is in perfect accord with the diffu- 

 sion theorj^, for we would expect the unstirred laj^er to be thinner when the 

 stirring was rapid than when slow. 



