ON OUR KNOWLEDGE OF SPECTRUM ANALYSIS. 



315 



The refraction-equivalent of myristicol' agrees ■well with numbers 

 characteristic of compounds of the aromatic series. It may be inferred 

 from these facts taken together that this substance is composed largely, 

 but not wholly of some benzene derivative. 



The refraction-equivalent of carvole is also abnormal, like that of 

 bodies of the aromatic series. Its absorptive power is remarkable, it still 

 being very considerable even when the substance is diluted to 1 in 300,000 ; 

 whereas the absorption-band in the case of myristicol has practically 

 disappeared at about 1 in 20,000. Similarly bergamot may be shown to 

 be a mixture of a terpene with a benzene derivative, and oil of peppermint 

 to be composed entirely, or nearly so, of a benzene derivative. 



The following is a summary of 

 the conclusions drawn regarding Oil of aniseed. B.P., 220-223° C. Theabsorption- 

 the terpenes : — ^and is due to anethol, C6H4 | (^jj^ 



1. Terpenes, with the composi- 

 tion CioHjg, possess in a high de- 

 gree the power of absorbing the 

 ultra-violet rays of the spectrum, 

 though they are inferior in this re- 

 spect to benzene and its derivatives. 



2. Terpenes, with the compo- 

 sition C15H24, have a greatly in- 

 creased absorptive power. 



3. Neither the terpenes them- 

 selves, nor their oxides nor their 

 hydrates, exhibit absorption-bands 

 under any circumstances when 

 pure, but always transmit continu- 

 ous spectra. 



4. Isomeric terpenes transmit 

 spectra which generally differ from 

 one another in length, or show 

 variations on 

 diluted. 



5. The process of diluting with 

 alcohol enables the presence of 

 bodies of the aromatic series to be 

 detected in essential oils ; and even 

 in some cases the amount of these 

 substances present may be approxi- 

 mately determined. 



The accompanying diagram 

 may be taken as typical of the ab- 

 sorption-spectra referred to. The 

 light portion represents the region 

 of absorption. 



The results so far obtained by Professors Hartley and Huntington 

 naturally led to the consideration whether substances with two doubly- 

 linked adjacent carbon atoms exhibit any bands in their absorption- 

 spectra, and other similar questions. These points have been independently 

 investigated by Prof. Hartley, since his appointment to the Royal College 

 of Science, Dublin.'* 



• Gladstone, Jom: C/iem. Foe. vol. xxiii. p. 149, 

 ' C/tem. Soc, read June, 1880. 



the substance being 



Absorption still strong at 300,000. 



