2 Dr. E. J. Mills on Isome?ism. 



but not as certainly offering true instances of isomerism. The 

 illustrious writer, with his usual caution, was willing to classify, 

 but no doubt thought it too early to speculate. 



Dumas, however, in the course of the next year published a 

 formal essay*, having been led to do so on account of Robiquet's 

 opinion as to the identity of chlorine, bromine, and iodine, and 

 also from the discovery by Wohler of the artificial formation of 

 urea. He states at the outset his inability to conceive the mo- 

 lecules of matter assorted at random (disposees au hasard) in a 

 definite organic combination ; the harmony of their arrangement 

 can, it appears to him, be foreseen from analogy and demon- 

 strated by experiment. His previous study of the ethers, indeed, 

 enables him to arrive at a conclusion which he thus states: — 

 " Nearly all the combinations of organic nature contain carbon 

 in two conditions. To take the simplest case, that of a compound 

 analogous to an ordinary salt, we find an oxygenated carbon 

 acid united to a carbide of hydrogen. The carbon, then, is at 

 once positive in the acid and negative in the base " (p. 329) . 



Shortly after he remarks, " organic isomers can easily be 



conceived to exist. Those which have the same atomic weight 

 are produced, I consider, by different binary combinations. In 

 those which have different atomic weights we see the same com- 

 binations more or less condensed " (p. 331). Isomerism, how- 

 ever, is a very general and also a gradual phenomenon. "Iso- 

 merism .... appears capable of affecting all bodies more or less 

 profoundly" (p. 332). And again, "If we conceive any sub- 

 stance possessed of a certain molecular arrangement which can 

 be permanently modified, we shall thereby be able to impress 

 upon it more or less profound isomeric modifications 3} (p. 332). 

 The various degrees of intensity of these modifications are de- 

 tailed. Thus the commencement of isomerism consists in changes 

 of hardness, cohesion, crystalline form, &c, the chemical proper- 

 ties remaining the same ; as in the two kinds of sulphur. If 

 this molecular movement continue, the chemical properties will 

 alter, but the atomic weight remain unchanged. At this stage 

 the molecular groups have undergone an essential alteration. 

 Lastly, the atomic weight is disturbed — either from the atom 

 admitting a greater number of elementary atoms, or from an ob- 

 vious shifting in the arrangement of binary compounds. All 

 combinations are assumed to be of binary constitution — this 

 being supposed demonstrable in voltaic decompositions, as well 

 as in those brought about by other physical and chemical means. 

 The essay concludes with an attempt to prove, from certain rela- 

 tions among their atomic weights, that the elements themselves 

 offer instances of isomerism. It appears evident that Dumas 

 * Ann. de Chim. et de Phys. vol. xlvii. p. 324. 



