324 liTHERliAL OILS-. 



volatile oiLs, which chemists class as Terpine, are dis- 

 persed in the air, because the}' ox^•dise the most rapidly. 

 It is ph\'siolog'ically interesting- to test the susccptibilit}' 

 of our sense of smell to perfumes. A few milligrammes 

 of musk are sufficient to scent exep a well-ventilated 

 room for ^ears. We smell this musk, and ^•et there can 

 be onh' an iniinitesmal quantity in the air which surrounds 

 us. Experiments made by Pass^', with alcoholic solutions 

 of strong smelling substances, have proved that the five- 

 hundred-thousandth part of a milligramme of \'anilla is 

 sufficient to appreciably' perfume a litre of air. The 

 same effect is obtained by live thousandths of a milligramme 

 ot camphrir : five millionths of a thousandth part of a 

 milligramme of artilicial musk sufficed to be perceived b)- 

 the olfactor\' nerves. Expressed in figures this would 

 be: 0.000,000,000,005 of a gramme: and yet the suscep- 

 tibilit\- of our organs of smell is considerabh' inferior to 

 that of man\' animals. 



In their principal chemical constituents ethereal oils 

 show no great complexity'. The elements carbon and 

 h\'clrogcn enter into them all : oxygen is generally present 

 in larger or smaller i.|uantities and sometimes nitrogen or 

 sulphur. But simple as this ma^' seem at first sight, we 

 find it to be more complicated when a closer investigation 

 is made into the constitution of these substances. We 

 owe to the works of the chemist Otto M'allach, of 

 G(ittingen, a further, ^'et not complete, acciuaintance of 

 the sLibject. I^ut only those who are N'crsed in the whole 

 range of Chemistry' will be able to follow the scientific 

 treatise on this question. 



