6 Dr. E. J. Mills on Isomerism. 



has since published a special work on isomerism*. The facts of 

 which he discourses are thus explained at the outset. M There 

 are three predominating principles in chemistry — the nature of 

 the elements, their relative proportion, and their arrangement. 

 We are about to consider but one of these — to inquire what may 

 occur if we suppose the same elements combined in the same 

 proportions, their relative arrangement only being made to vary. 

 This is the problem of isomerism" (p. 5). "I call isomeric bodies 

 those which are formed of the same elements united in the same 

 proportions, but presenting different properties, a proof of a dif- 

 ferent arrangement" (p. 5). Simple and compound substances 

 are included in his definition. Physical isomerism has to do 

 with purely physical causes ; magnetized and unmagnetized iron 

 are instances of it. u Generally the transformation of a body 

 into an isomer gives rise to a calorific phenomenon — that is, to a 

 disengagement or absorption of heat" (p. 15). The classifica- 

 tion given is substantially the same as his previous one ; only a 

 fifth division is made (kenomerism) to include " bodies formed 

 by the elimination of different or identical elements, at the ex- 

 pense of distinct compounds" — as when glycol losing water, and 

 ethylic alcohol losing hydrogen, produce ethylenic oxide and alde- 

 hyde respectively. The allotropy of the elements is discussed 

 at considerable length ; and the author expresses his belief in 

 the doctrine of the fundamental unity of matter, — a conclusion, 

 indeed, common to several writers on isomerism, and which may 

 be said to have descended to us from the earliest times of philo- 

 sophical speculation. Berthelot's treatise is not characterized by 

 many theoretical novelties, but, as a comprehensive account of 

 the present position of isomerism, it cannot fail to be interesting 

 and valuable to the general chemical reader. 



Crum Brown f has recently examined the theory of differences 

 in units of affinity, and finds that there is nothing absurd in the 

 theory itself, but that Butlerow's special mode of treatment leads 

 to contradictory results. He gives the name " absolute " isomers 

 to those of which rational formulae furnish no account. The 

 molecules of several isomers are graphically represented, this 

 special notation being fundamentally that of Dalton, to which 

 straight lines have been added to indicate " bonds " J or units of 

 affinity. 



The history of but few theories can yield so remarkable a re- 

 sult as follows from the preceding narration. With an almost 



* Legons sur I'lsomerie, 1863. 



t "On the Theory of Isomeric Compounds," Trans. Roy. Soc. Edinb. 

 1864, p. 707. 

 X Frankland, Chem. Soc. Journ. [2] vol. iv. p. 377- 



