708 DR A. CRUM BROWN ON ISOMERIC COMPOUNDS. 



metameric ; in other words, whether the theory of atomicity is insufficient alone 

 to explain their difference. 



1. Are there two isomeric series having the common formula C„H,(n+i) ? 

 Or are these bodies identical ? Till lately, most chemists would have replied 

 unhesitatingly that these substances were different. According to the observa- 

 tions of Frankland, hydride of ethyl and methyl gas, otherwise so like qne 

 another, show a very different reaction when treated with chlorine in diffused 

 day-light. Were this observation confirmed, it would be quite sufficient to prove 

 that the two bodies were not identical. Several chemists (Cakius, Schorlemmee) 

 have, however, lately expressed doubts as to the correctness of Frankland's 

 observation, and it would certainly be satisfactory that it should be repeated 

 with special precautions. 



That these bodies are not metameric, that is, that the theory of atomicity is 

 incapable of explaining the difference between them (assuming, as we may do. 

 till Frankland's observation be found incorrect, that there is a difference), is 

 evident. For there is on that theory only one possible constitutional formula for 

 a substance having the composition and molecular weight expressed by the 

 empirical formula C.^Hg, viz., 



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 The same reasoning is sufficient to show that the other pairs in this series, as 

 methyl-ethyl and hydride of propyl, ethyl and hydride of butyl, &c., are not 

 metameric. The question of the identity of these bodies must, however, be still 

 regarded as an open one. 



2. There can be little doubt that chloride of ethyl and the substance produced 

 by the reaction of chlorine on hydride of ethyl are essentially different. The 



* I may here shortly explain the graphic notation which I employ to express constitutional 

 formula, and by which, it is scarcely necessary to remark, I do not mean to indicate the physical, 

 but merely the chemical position of the atoms. An atom is represented by its usual symbol, 

 surrounded by a circle with as many lines proceeding from it as the atom contains equivalents, thus 

 an unequivalent atom is represented by Q— , a biequivalent atom by — @— or ©Z, and so on of 

 the others. When equivalents mutually saturate one another, the two lines representing the 

 equivalents are made continuations of one another, thus water is (h) — (V) — Q. Formic acid 



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r 



&c. 



(i) 



This method seems to me to present advantages over the methods used by Professors Kekule 

 and Erlenmeyer ; and while it is no doubt liable, when not explained, to be mistaken for a repre- 

 sentation of the physical position of the atoms, this misunderstanding can easily be prevented. 



