ON THE CONSTITUTION ETC. OF ESSENTIAL OILS. 



217 



G. Cymene from Hesperidene Dibromide. 



H. Cymene from Nutmeg-terpene Dibromide. — This cymene, of course, also 

 contained the cymene which preexisted in the hydrocarbon used ; the pre- 

 existing cymene was about 10-12 per cent, whilst the total cymene obtained 

 was 55 per cent, of the hydrocarbon used. 



The following were the physical characteristics of these specimens : — 



Each of these eight specimens gave analytical numbers agreeing with the 

 formula Cj^H^^. On oxidation with dichromate of potassium and sulphuric 

 acid the same result was obtained in each case ; viz. pui-e terephthalic acid 

 was obtained in quantity varying from 30 to 60 per cent, of hydrocarbon 

 used, no isophthalic acid being formed, and acetic acid perfectly free from 

 higher homologues was obtained, the results being verified by analysis of the 

 products. 



It is hence inferred that only one kind of cymene exists, and that that 

 boils at very close upon 176°-5, having a specific gravity of 0-860, a specific 

 dispersion of 0-0405, and a refraction-equivalent of 75-0. The production 

 of this cymene from four isomeric terpenes, viz. turpentine-oil (Williams, 

 Barbier, Oppeuheim), citrene (Oppenheim), hesperidene (Wright), and nut- 

 meg-terpene (Wright), gives rise to many speculations as to the mutual 

 relations of these substances. It may be noticed as regards their formulariza- 

 tion in accordance with modern conventions, that Kekule's formula for benzene 

 permits of the ascription of three formulae only for bodies that are dihydrides 

 of cymene if this hydrocarbon be viewed as a 1-4 benzene derivative, but of 

 six if it be considered a 1-2 derivative or a 1-3 derivative. If, there- 

 fore, it be assumed, as seems most probable, that cymene belongs to that 

 series to which 1-4 formulae are ascribed, it must be supposed that at any 

 rate one of these four terpenes is either a 1-2 or a 1-3 derivative. Now, 

 whatever may be the actual nature of the process symbolically indicated by a 

 transference of a group of symbols from one part of a " structural '' formula 

 to another, it is pretty evident that it must correspond to the performance of 

 work of some kind, and hence is intimately connected with the subject 

 touched upon above, vi^. the relations between " Intrinsic Chemical Energy " 

 and Isomerism. Were it possible to estimate the amounts of heat involved 

 in the reactions 



C,„H, + Br,=C,H,,Br, 



C,„H,,Br, =2HBr-HC,„H,, 



