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Mr. J. E. Marsh. Researches on the [Dec. 5, 



isomers which, shall be the optically opposite isomers of these two. 

 In this latter case, therefore, the two acids will also be related, as 

 male'ic and f umaric acids, but the laevo-acid will correspond to male'ic 

 and the dextro- to fnmaric. This laevo-camphoric acid is without 

 doubt the acid which Chautard obtained by the oxidation of laevo- 

 camphor, and the fumaroid dextro-acid I hope to obtain from it by 

 the hydrolysis of the acid chloride. 



Now, accepting unreservedly Van't Hoff's carbon-atom hypothesis, 

 we find that the isomerism of the camphoric acids is not explained by 

 different structural formulas, but rather by one and the same structural 

 formula, admitting of at least four different arrangements of the 

 atoms in space. There will be then two conditions attached to such 

 a structural formula : (1) Either it will contain two doubly-linked 

 carbon-atoms, each of them being united to two different groups, and 

 one of these groups containing also an asymmetric carbon-atom ; (2) 

 or the formula may consist of a closed chain of carbon-atoms, of which 

 two or more are asymmetric. In the latter case, it is necessary to 

 mention a further restriction, namely, that when there are only two 

 asymmetric carbon-atoms in the ring, there must not be symmetry in 

 the formula, or, in other words, the image of neither isomer must be 

 identical with its object (see ' Phil. Mag.,' 1888, vol. 26, p. 426). It 

 is the more necessary to mention this restriction as it applies to 

 Wreden's formula, a formula which does not admit of rotatory power 

 in the maleinoid acid, that is, in the ordinary camphoric acid. 



Turning now to some of the formulae proposed for camphoric acid 

 by different chemists, we find that in general they satisfy one or other 

 of the conditions before mentioned. But Kekule's formula, which 

 fulfils the first condition, and Kachler's, which satisfies the second, 

 cannot be accepted, on the ground that they do not represent cam- 

 phoric acid as a derivative of hexahydrometaxylene. Wreden's 

 formula which does thus represent camphoric acid does not, as I have 

 just mentioned, satisfy the restricted second condition. Armstrong's 

 formulae satisfy the second condition, and also represent camphoric 

 acid as a derivative of hexahydrometaxylene, but Armstrong's for- 

 mulae appear to me liable to objection on the ground of the formula 

 for camphor from which they are derived. These formulae represent 

 camphor either as not containing a ketonic group, or if it contain a 

 ketonic group as containing also a closed chain of four carbon-atoms. 

 Now, we know no instances of stable rings of four carbon-atoms, if 

 indeed we know instances of such rings at all ; and it is unlikely that 

 camphor is the one exception to what may be regarded as a general rule. 



The formulae which I have proposed for camphor and camphoric 

 acid appear to be opposed by no facts, and also explain perfectly the 

 isomerism of the camphoric acids. Camphor is represented by the 

 formula — 



