CHEMISTRY. 



CHAPTER I 



INTRODUCTORY. 



1. Difference between Chemistry and Natural Philosophy. 

 Chemistry treats of the composition of substances, while 

 in Natural Philosophy, or Physics, their mechanical con- 

 ditions and relations alone are regarded. For example, in 

 Natural Philosophy we look at the laws governing the 

 pressure and movements of water, while in Chemistry we 

 inquire of what water is composed, and into the composi- 

 tion of what substances it enters. And so of other sub- 

 stances solid, liquid, and gaseous. 



2. Elementary Substances. In making its investigations, 

 chemistry decomposes such substances as are composed of 

 two or more things. When any substance is found that 

 can not be decomposed or separated into two or more 

 things, it is termed an element, or an elementary substance. 

 On the other hand, all those substances which can be de- 

 composed are called compound. Iron is an element, for it 

 can not be decomposed : it is one thing. But iron rust is 

 a compound substance composed of three things, for water 

 and a gas called oxygen, existing in the air, unite with iron 

 to form rust. 



