44 J)i'. W. Odling on the Doclrinc of Equivalents. 



bodies, but simply as useful means of manifesting their relations 

 and modes of formation. 



Kokule has recently published a paper in whicli these views 

 are brought forward more definitely, and with an amount 

 of illustration heretofore not possible. He has shown how the 

 abstraction of hydrogen increases the basicity of the radical, and 

 how compounds containing mult-equivalcnt radicals may be 

 rationally represented by several formulse. Semi-benzidine, for 

 instance, may be represented either as a di-aramonia, in which 

 two atoms of hydrogen are replaced by the bi-equivalent radical 

 (C^ H"*)", or else as benzine, in which two of hydrogen are replaced 

 by two of amidogen, &c. * 



The circumstance that the single atoms of certain elements 

 and groupings have each the property of replacing two, three, or 

 more atoms of hydrogen by equivalent substitution, that they 

 are, in fact, mult-equivalent, is now, I believe, generally admitted. 

 But, prior to the recognition of mult-equivalent radicals, 

 Gerhardt, who first pointed out the difference between the atomic 

 weight and equivalent of an element, contrived to make all atomic 

 weights correspond with the hydrogen equivalent, by according to 

 several of the elements two distinct atomic weights. Thus, for 

 iron we had two atoms, ferrosum = 28, and ferrieura = 18"7; for 

 platinum we had two atoms, platinosum=98*5, and platinicum 

 = 492 ; for bismuth, antimony, and aluminium we had bismi- 

 thicum, antimonicum, and aluminicum respectively. Gerhardt 

 certainly employed ferricum and its congeners in an atomic sense, 

 and Laurent distinctly argued that they had every right to be 

 considered as atoms. Each of these atoms was respectively equiva- 

 lent to an atom of hydrogen, and was represented by its own par- 

 ticular symbol, as illustrated in the following chlorides : — 



Fe CI ferrous. 



fe CI ferric (FFe'" CP = 3 fe CI) . 



Pt CI platinous. 



ptCl platinic (Pt"CP = 2ptCl). 



Mci'brstz:}(K'"ci'=3bici). 



al CI aluminic (AAF CP = 3 al CI). 



These formulse are, I conceive, perfectly admissible, and occa- 

 sionally very commendable, if used merely to represent equivalent 

 quantities ; but if used to represent the atoms of the elements, 

 or the smallest indivisible proportions of the elements which 

 can enter into combinations, they are, I conceive, incorrect. 

 From my acquaintance with Gerhardt, I believe that latterly, 

 after he had begun to employ mult-equivalent radicals, he was 



* Annalcn der Chemie tind Pharmacie, civ, 129, 1857. 



