80 ROYAL SOCIETY OF CANADA 



namni's work comes here, 1891), and finding quantitative relations 

 wliere the latter had seen none. Noyes used this method nimiber three 

 in his own work, and discovered the first reactions of the third order 

 studied since the time of Hood. 



The next incident is the appearance of the second edition of Ostwald's 

 Lehi-buch, or rather of the second ectition of vol. 2, part 2, Heft 2, with 

 the chapter on kinetics. In tliis, after reviewing the methods of working 

 in common use, viz. : methods three and four of our classification, 

 Ostwald suggests working with all the chemicals but one in excess, and 

 determining the effect of that one on the rate — Harcourt's method, so 

 far. Harcourt's name is not mentioned at all in this connection, how- 

 ever, and reading a little further shows that it is not Harcourf s method 

 after aU; because when it comes to determining the efi'ect of the con- 

 centration of B on the rate, instead of preparing the experiments with a 

 different excess of B, it is proposed to make b small in turn, and so with 

 aU, one after the other. The method used in Harcourii's paper seems to 

 have been quite forgotten. 



^¥hen planning work for the laboratory for the winter of 1902, I 

 read this new method of Ostwald's with the greatest interest, and fully 

 appreciated the advantages set out so clearly by the author. 



On thinking over the case in which I was specially interested, how- 

 ever (the reaction between chloric and hydriodic acids in presence of free 

 iodine) I found that the effect of the iodine concentration could not be 

 ascertained, by this new method; to ascertain it, it would be necessary to 

 make up a solution, in which the concentration of the iodide was much 

 lower than that of the others, including that of the iodine. Now, it is 

 impossible to prepare a solution containing much iodine and little iodide, 

 Uie iodine won't dissolve. And on further thought, I saw that my object 

 could be attained by comparing the rates in two solutions, in both of 

 which the iodide was in excess, but different excesses. The method of 

 Harcourt again, at last. 



I didn't know it was Harcourt's at first ; in fact, it was only in the 

 winter, when the work was well advanced, that in connection with some 

 work that Mr. Bell ^ was doing, I had occasion to read Harcourt's paper, 

 and found what I had begun to regard as my method clearly described. 

 This tool once in our hands, it is not surprising that we should be 

 able to solve problems that had proved too much for some of the best 

 known chemists working under less favourable circumstances. 



Tlie rates of oxidation of hydriodic acid, for instance, by the oxy- 



»Jour. Pbys. Chem., 7, 61 (1903). 



