DR A. CRUM BROWN ON ISOMERIC COMPOUNDS. 716 



transition from acetonitrile to hydride of ethyl ; and, 3. That hydride of ethyl is 

 not identical with methyl gas. 



By carrying this argument a little further, and making use of no additional 

 assumption, we arrive at an absurdity,— thus, the carbon radical of the acetic 

 series is the same as that of oxyacetic (glycollic) acid, that again is the same as that 

 of oxalic acid, therefore as that of oxalic nitrile or cyanogen gas ; but in cyanogen 

 gas we have the two carbon atoms united by two primary affinities ; but we have 

 before proved, that in the acetic series they are united by a primary affinity of the 

 one, and a secondary affinity of the other. It is obvious, then, that at least one of 

 our assumptions is false. And when we closely examine the two general assump- 

 tions (1. and 2.), we shall see reason to believe, that neither of them is rigidly true. 



It is well known that the replacement of one equivalent in a compound by 

 another, while it leaves the " chemical structure," or " chemical position" of the 

 other atoms unchanged, exerts an influence on the intensity of the chemical at- 

 traction, not only of the equivalents directly concerned in the replacement, but of 

 all the equivalents in the molecule.* To see this we have only to compare the 

 nature of the force, uniting H to O in acetic acid, and in GlycocoU, 



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We here see the hydrogen and the ammonia residue NH^ exerting a " disturbing" 

 influence on the relation of oxygen to hydrogen through two carbon atoms. Many 

 other examples will at once occur to every chemist. The nature of the equivalents, 

 that is, of the force they exert, is thus seen to be variable, but the facts of abso- 

 lute isomerism force us to admit, that this variation in the character and intensity 

 of the chemical force exerted by the difterent equivalents of one atom depends 

 upon something else, as well as upon the nature of the other equivalents with 

 which that atom is united. 



We find, then, that although the nature of one equivalent of an atom does 

 change, as the other equivalents are united with different substances, there must 

 be some original difference between them, which renders absolute isomerism pos- 

 sible. In what this original difference consists, whether it is essential or merely 

 accidental (using the word in its strictly logical sense), we cannot as yet say. 



We may thus divide the force, uniting any two equivalents, into two com- 



* BuTLEROw notices this disturbing influence (Zeitschrift, vi. 516) as opposing an obstacle, which 

 he seems to regard as for the present insuperable, in the way of determining whether a difference 

 exist or not among the equivalents of a multequivalent atom. 



VOL, XXIII. PART III. 9 F 



