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ROYAL SOCIETY OF CANADA. 



distinguished two ways of trying, or testing the assumptions 

 by experiment. I shall not enlarge on these further than to say thaA the 

 better way, the sliarpcr test, involved comparing experiments in which 

 tlie initial concentrations of the chemicals were varied, while the other 

 relied altogether on the results of a series of analyses of the same solu- 

 tion at different intervals of time. The first of these methods was used 

 by van't Hoff in his book, the other, exclusively, by his successors, for 

 twelve years. 



To resume, then, thene are shown in this table four ways of deter- 

 mining the relation between the rate of a chemical reaction and the con- 

 centrations. Systematic exploration, Harcourt and Esson, 1866 ; a 

 hybrid method, 1878 ; and the method of guess and try, with two ways 

 of trying, of which the better was used by van't Hoff in 1884, and the 

 other w^as in general use between 1884 and 1895. 



Method. 



1 . Systematic Exploration — 

 Harcourt & Esson's. . . 



2. Hybrid 



Guess and Try 



3. (a) varying initial cone's. 



4. (b) varying time only... . 



5. The logical extreme • . . . 



Definition. 



a, B, C, D, ...T 

 a, b, C, D, ...T 

 a, 1), c, d, . . .T 



a, b, c, d, . • .t 



Used by 



H and E, 1866 

 Hood, 1878 



van't Hoff, 1884 

 General, 1885-1895 

 Not employed 



I should like to put aJl tliis in a diagram; tliat will make it look 

 more like physical chemistry. The only trouble is what co-ordinates to 

 use. The dates will do for the abscissas, that's obvious, and I will put 

 Harcourt and Esson high up, because the method they employed was the 

 one best adapted for the purposes of discovery, and Hood a little further 

 down, and then van't Hoff, with the method of varied initial concentra- 

 tions, and then all the chemists from 1885 to 1895. So that the abscissae 

 are chronological, and the ordinates psychological. 



I would not like to give the impression that van't Hoff, for instance, 

 used a method that was unsuitable for the purpose he had in hand. He 

 had a definite object, and his method enabled him to attain it. In Hood's 

 case, too, there was a special reason — not a vei*y good one, perhaps — 

 that kept him from using method number one; and he too got all he 

 wanted with number two. But the fact is plain, that as time went on, 



