Examination of Essential Oils. 



15 



Substances causing strong absorption bands in the spectrum transmitted by 



dilute solutions. 



The following oils and derivatives of essential oils show strong- 

 absorption bands in their photographed spectra. For the most part 

 they are bodies known to contain the aromatic nucleus as an essential 

 part of their constitution. Thus the oils of bay, pimento, and cloves 

 contain the substance eugenol, C 6 H 3 .OH.OCH 3 .C 3 H 5 ; oil of cassia con- 

 sists of cinnamic aldehyde, C 6 H 5 .C 2 H 3 .COH ; and oil of aniseed contains 

 anethol, C 6 H 4 .OCH 3 C 3 H 5 ; and oil of thyme, thymol, C 6 H 3 .OH 3 .C 3 H 7 , 



Some other oils, such as bergamot and oil of peppermint, as like- 

 wise the bodies menthole, carvole, and myristicol, have an unknown 

 constitution. The three latter substances are known to be isomeric. 

 (" Journ. Chem. Soc," Gladstone, vol. xxv, p. 1.) 



Great interest is attached to our examination of these, since we con- 

 sider it to be proved from the character of the spectra they transmit, 

 that the nucleus of menthole is a terpene, while the benzene ring is 

 the inner basis of carvole and myristicol. Bergamot appears to be a 

 terpene mixed, with some derivative of the aromatic series, but oil of 

 peppermint on the other hand is essentially a substance belonging to 

 the latter class. 



Oil of Bay (Dr. Gladstone). — There was a fair quantity of this 

 substance, and the following fractions were separated by distilla- 

 tion : — 



1st fraction boiling at 190—200° C. 

 2nd „ „ 200—220° ,, 



3rd „ „ 220-240° „ 



4th „ „ 240—260° „ 



The two principal fractions boiling at 190 to 200°, and from 220 

 to 240°, were photographed. 



The fraction boiling between 190 — 200° solutions containing 10 1 00 , 

 s oW tmoo- aild lok were examined. 



The first absorption band commenced midway between lines 12 and 

 17 Cd, and in a solution containing 50 1 00 of the oil, this continues 

 nearly to the line 18 Cd ; at this point a narrow band of rays is trans- 

 mitted. The widening out of this band is somewhat rapid between 

 two 05 and tmoo) after which it is somewhat more gradual, there being- 

 still some absorption at 1 in 50,000. 



The fraction boiling between 220 — 240° solutions containing 1 in 

 1,000, 5,000, and 10,000 were photographed. The absorption in these 

 solutions appears at nearly the same points, but is more intense. This 

 is quite what one might expect supposing the fraction with the higher 

 boiling-point to contain a greater proportion of the absorbing body 

 than the other. 



