34- Chemistry. [Lecture 25. 



is added it will drop the iron, and unite with the 

 alkali. The body thus let fall is said to be pre- 

 cipitated, and is called a precipitate, and the sub- 

 stance which is employed to cause its precipitation 

 is called a reagent. 



These observations may serve to afford a ge- 

 neral idea of the effects of heat and mixture. In 

 the remainder of this lecture I shall endeavour 

 to give an outline of the principal doctrines of 

 modern chemistry, and particularly with respect 

 to the simple substances. I shall in the two fol- 

 lowing lectures proceed to point out more par- 

 ticularly the chemical effects of heat and mix- 

 ture. I shall next describe the chemical apparatus 

 or instruments; and shall then briefly examine 

 and explain the nature and properties of mineral 

 substances, salts, earths, metals, combustibles, 

 and waters, as far as chemistry has made us ac- 

 quainted with them; and lastly shall treat of 

 vegetable and animal substances in the same 

 manner, particularly as to the nature of their 

 constituent parts. 



It is one of the great uses of philosophy to 

 make us better acquainted with an intelligent 

 Providence, to show how wisely and with what 

 infinite design all things in the heavens and on 

 the earth are disposed; and every step we advance 

 affords fresh cause for admiration. You have 

 just been contemplating the wonders of the fir- 

 mament. Those which modern chemistry dis- 

 plays to your view, though on a minuter scale, 



