Combustible Substa nces. 219 



the spirit and acid in the ordinary way, only al- 

 lowing more acid. He set the mixture by, well 

 corked, and after some time found the ether 

 swimming at the top, with a watery fluid at 

 bottom. This process is disagreeable, on ac- 

 count of the vapours and the danger of burst- 

 ing the vessel. There are also a muriatic and 

 acetic ether. 



3. OILS are combustible substances formed by 

 nature in animal and vegetable bodies. They 

 may be distinguished into two principal kinds ; 

 the volatile and the fixed. 



1st. The volatile aromatic or essential oils 

 affect the tongue generally with great pungency 

 and heat, and have all more or less <)dour, ge- 

 nerally strong. They have no smoothness, slip- 

 periness, or unctuosity when felt between the 

 fingers, a quality that belongs to the fixed or 

 unctuous, which are particularly bland to the 

 taste and smell ; and these two qualities distin- 

 guish them, viz. want of taste and of smell. 

 \Vhat have been called the empyreumatic re- 

 semble so much the aromatic, that they are only 

 distinguished by their origin, being produced by 

 means of fire. 



Volatile oils, as well as the fixed, are com- 

 posed chiefly of two ingredients, hydrogen and 

 carbon, but they contain a larger proportion of 

 hydrogen than the fixed oils, from which they 

 may easily be distinguished, as when dropped on 

 paper and evaporated they leave no mark or stain 



L2 



