Combustible Substances. 



unchangeable; hence it is common to scorch 

 ends of stakes, &c. which are to be put in the 

 earth, and when thoroughly charred, there is 

 scarcely an end of their duration. Neither 

 moisture, air, nor any thing else affects charcoal 

 as long as it continues cold, nor even heat itself 

 alone, provided the charcoal is kept in close ves- 

 sels. The explosion of gunpowder greatly de- 

 pends on the charcoal it contains, which fur- 

 nishes an essential ingredient of that volume of 

 air which expands upon every explosion. 



II. Of the compound combustibles. Dr. 

 Thomson most judiciously remarks that they 

 are almost all combinations of carbon and hy- 

 drogen, or of carbon, hydrogen, and oxygen. 

 They comprehend a great part of all vegetable 

 and animal substances. But from the present 

 imperfect state of chemical science, and still 

 more from the nature of these lectures, which 

 are only elementary, we must confine ourselves 

 to the following : 1, Alcohol, or ardent spirits ; 

 2, Ether; 3, Volatile oils; 4, Fixed oils; 5, 

 Tan. 



1st. ALCOHOL, or ardent spirits, have the lat- 

 ter name from their inflammability and volatility. 

 The old chemists gave the name of spirit to 

 every subtile penetrating liquor obtained by dis- 

 tillation. It is called ardent to distinguish it 

 from those that are not inflammable. When 

 most pure, it is called rectified spirit of wine, or 

 alcohol. It is obtained by fermentation from 



