Mr. M. M. Pattison Miiir on Chemical Classification. 89 



pound radicles as imagined by the school of Berzelius was 

 exceedingly distasteful to the substitutionists. The properties 

 of a compound depended, in their view, not so much upon the 

 elements which it contained as upon the position of these 

 elements. 



We have in the idea of substitution, as a guide in classifi- 

 cation, a distinct advance upon the idea of dualism. The 

 sole point upon which the attention must be concentrated is 

 not, says the upholder of substitution, the composition of a 

 substance ; we must also pay regard to its reactions, whether 

 of formation or of decomposition. The new school therefore 

 attempted to combine the older method of the study of reac- 

 tions with the newer method of the study of composition; only 

 it made the former study of real importance by giving it a 

 quantitative significance. 



At first the substitutionists were too eager, too inclined to 

 regard position of the component elements as all important. 

 Elated with the success which had attended their attacks upon 

 the clumsy and often contradictory formulae of dualism, they 

 for a moment forgot the truths which dualism typified. Espe- 

 cially did they oppose themselves in opposing the conception 

 of compound radicles. But they wanted many new facts 

 before a satisfactory theory could be established. Destruc- 

 tive criticism could be carried on with the aid of but few 

 facts ; the construction of a new wide-spreading generaliza- 

 tion was only to be hoped for as the result of long-conti- 

 nued and exact labour. 



9. The facts which the upholders of substitution gathered to- 

 gether, taken along with those already amassed by their prede- 

 cessors, soon obliged the adherents of the new school to 

 look on the nature of the substituting element or radicle as 

 influencing the nature of the compound. Thus, by substi- 

 tuting potassium in place of part of the hydrogen of water 

 a strongly alkaline substance was produced ; by substituting 

 the group NO2 for the same hydrogen, a strong acid w^as 

 formed. The two products differed widely in their proper- 

 ties ; nevertheless they might be both regarded as derived 

 from the same original substance by substitution. Such ex- 

 periments as this led to the idea of substituting radicles, 

 which was again developed into the modern doctrine of com- 

 pound radicles, — to the idea of types, which subsequently found 

 its fullest expression in the general theory of valency, — and, 

 lastly, to the reconcilement of the two ideas formerly opposed — 

 namely, that all depends upon the position, and that all depends 

 upon the nature, of the elements or radicles in a compound 

 body. 



