PROCEEDINGS 



OF 



THE ROYAL SOCIETY. 



Researches on the Action of Organic Substances on the Ultra - 

 Violet Rays of the Spectrum. Part III. An Examination 

 of Essential Oils." By W. N. Hartley, F.R.S.E., &c, Pro- 

 fessor of Chemistry in the Royal College of Science for 

 Ireland, Dublin, and A. K. Huntington, F.C.S., Associate of 

 the Royal School of Mines. Communicated by Professor 

 Stokes, Sec. R.S. Received July 22. Read November 20, 

 1879. 



Much chemical and physical research has been devoted to the class 

 ■of bodies known as essential oils, as, for instance, the investigations of 

 Dr. J. H. Gladstone ("Journal of the Chemical Society," vol. xviii, 

 p. 1 ; vol. xxiii, p. 147 ; vol. xxv, p. 1), of Dr. C. R. A. Wright 

 ("Isomeric Terpenes and their Derivatives," vol. xxvi, pp. 549 and 

 686 ; vol. xxvii, pp. 1, 317, and 619), and of Dr. W. A. Tilden (loc. 

 cit., vol. xxviii, pp. 514 and 1258), as well as many others. 



It is now well known that essential oils consist for the most part of 

 isomeric hydrocarbons, which may be divided into three polymeric 

 groups, possessing the composition denoted by the f ormulas — 



^10^16 C 20 H 32 . 



To the first class belong the hydrocarbons derived from turpentine, 

 orange, nutmeg, myrtle, and several others, while the second group 

 includes the hydrocarbons from rosewood, cubebs, calamus, cascarilla, 

 patchouli, and cloves. The third group is represented by colophene. 

 Though of unknown constitution, these bodies exhibit a close rela- 

 tionship to benzene derivatives. 



Many of the oils are articles of great commercial value and conse- 

 quently are subject to adulteration, a fact which, in addition to the 

 scientific interest they possess, led us to submit a number of specimens 

 to examination in the spectroscope. 



We have to acknowledge assistance rendered to us by the kindness 

 of several gentlemen who supplied us with samples, namely, Dr. Glad- 



VOL. XXXI. B 



