Examination of Essential Oils. 



11 



Oil of Cedar Wood (Dr. Gladstone). — There was no distillate at any 

 temperature below 250° C, and only a few drops at 260°. 



1st fraction, boiling-point 260 — 265°. 

 2nd „ „ 265—270°. 



This oil, like several others, polymerises easily dnring distillation ; 

 consequently, a freshly distilled specimen on redistillation leaves a 

 resinous residue in the retort. The portion boiling between 265° and 

 270° was examined after diluting 1,000, 3,000, 6,000, and 10,000 

 times. (Diagram 7.) 



An examinatioD of the diagrams which contain the results of ob- 

 servations on the preceding substances will show that in bodies of the 

 same constitution the absorption of the ultra-violet rays is greater the 

 larger the number of carbon atoms in the molecule. That is to say, 

 the oils with the higher boiling-points such as calamus, patchouli, and 

 the denser turpentine oil, are those which are the least transparent 

 after dilution with alcohol. 



With two exceptions, none of the substances already examined 

 exhibit absorption bands. The exceptions alluded to are the first 

 specimen of carraway hydrocarbon, which we shall show further on, 

 containing a small quantity of cymene, and the blue oil from 

 patchouli. 



As we shall have occasion to remark on the evident presence of 

 cymene in several essential oils, it may be convenient to give an 

 account of specimens of cymene which we have examined, and direct 

 attention to the absorption bands which are made to appear by 

 diluting the liquid to various degrees, as shown in the diagram. 



Cymene No. 1. — This specimen was prepared by Dr. C. R. A. W right, 

 and examined optically by Dr. Gladstone. Its source was probably 

 oil of lemons. It began to distil at 172°, and nearly all the liquid 

 came over below 176° C. 



The portion boiling between 173° and 175° was completely soluble 

 in fuming sulphuric acid with only a pale brownish coloration. It 

 was examined first without dilution, and subsequently when diluted 

 to 1,000, 2,000, 4,000, 5,000, 8,000, 20,000, 50,000 and 100,000 

 volumes. Three well-defined absorption bands are visible with a dilu- 

 tion of 4,000 and 5,000 times ; a band similar to that lying below the 

 line 17 Cd appears to be characteristic of the hydrocarbons derived 

 from benzene. See diagrams of benzene, ethyl-benzene, mesitylene, 

 toluene, &c, in Part II of this research (" Phil. Trans.," Part I, 1879). 

 (Diagram 10.) 



Cymene No. 2. — About 250 grms. were obtained from Mr. 

 Kahlbaum's agents. The boiling-point of nearly the whole of it 

 lay between 173° and 176°. No portion of this was so pure as the 



