232 ROYAL SOCIETY OF CANADA 



action of the third order; N'03'es^'' showed by a recalculation based on 

 method three^ that tinder some circumstances, at least, it is of the first. 

 Mr. Forster,'^ who subjected the reaction to a "systematic exploration," 

 showed it had no "order" at all; tha,t the effect of increasing (tlie 

 concentration of the potash was first to increase and then to decrease the 

 rate. The relations found by Forster had not been guessed by liis pre- 

 decessors, and, consequently, were not revealed by their method of 

 working. 



The last reactions of which I shall speak, are the reactions gnouped 

 under the common name " induction." Here, twoi reactions take place 

 in the solution at once, and the rates of each are affected by the concen- 

 trations of four or more chemicals.^® The experimental study of compli- 

 cated cases like these is, to put it shortly, absolutely impossible by any 

 method other than that which I have called " systematic exploration." 

 Guess and Try is no good ; not that one can't guess — some people, I don't 

 know whether any chemists among them, are able to guess the result of 

 a honse race, or of a flurry in stocks — blut the " trying " needs the 

 systematic procedure. 



Manchot,-*' Schilow, and Luther ^^ guessed at the mechanism of tlie 

 induction by iron of the reaction between chromic acid and hydrogen 

 iodide. Miss Benson's experiments ^^ showed that they guessed wrong ; 

 and a long series of experiments by Mr. DeLury^^ on the induction of the 

 same reaction by arsenious acid, furnish the first proven case of induc- 

 tion according to the peroxide formula. No oither cases of induction have 

 been studied from this point of view; and no others can be, except by 

 this method. 



Working with this tool of Harcourt's, we have been able to sharpen 

 it a little, and extend its usefulness. Without going into details, it was 

 obviously only a short step to pass to the " method of constant rates,"-* 

 in which all the concentrations, and rates as well, are kept constant dur- 

 ing the experiments. 



"Zeit. phys. Chem.. /.S. 129 (1895). 

 "Jour. Phys. Chem.. 7. fi4() (1903). 

 "Jour. Phys. Chem.. //. 9 (1907). 

 ~Liebig's Annalen. S25, 9.^ (1902). 

 "Zeit. phya. Chem., /,o, 777 (1903). 

 «Jour. Phys. Chem.. 7. 356 (1903). 

 "Jour. Phys. Chem., 11, 54 (1907). 

 "Jour. Phys. Chem., 7. 92 (1903). 



