A PRIZE ESSAY. 
7 
are old names of things which you kni>w. Of the 
fifteen, you know nearly one half by name and by 
nature. These are potash, soda, lime, magnesia, iron, 
sulphur. Perhaps you will add, that you know car¬ 
bon is coal, or rather coal carbon. You have heard 
from some travelling lecturer at your town Lyceum, 
that oxygen and hydrogen together form water ; that 
oxygen and nitrogen form the air you breathe ; that 
nitrogen and hydrogen form ammonia, or sal volatile, 
which gives the sharp smell to the smelling bottle. 
Besides, the thing has been said so often that you 
must have heard it, that chlorine, the substance which 
bleaches in bleaching salts, united to soda, makes 
common salt; or if chlorine is united to ammonia, sal 
ammoniac is formed. Now by changes and combina¬ 
tions among these fifteen things, nature makes every¬ 
thing we find in plants. Many of these are invisible 
as is the air. The substance called chlorine perhaps 
you have never seen, but if you ever smelt it you 
will never forget it. It is often smelt in a piece of 
bleached cotton, when opened in the shops. It gives 
the smell to bleaching powder used to disinfect the 
air, during cholera and other diseases. If you could 
see it, it would appear merely a faint yellowish- 
green air. It is all-powerful on vegetation. As it 
forms a part of common salt, say half of its weight, 
we may dismiss the further consideration of it, by 
saying, that, in some shape or ether, chlorine is uni¬ 
versally diffused in soil and plants. 
CHEMICAL SUBSTANCES DEFINED. 
The list above may be divided as follows :—-First, 
the airy or volatile; secondly, the earths and metals; 
thirdly, the alkalies; fourthly, the inflammables. Only 
the third and fourth divisions require to be explained 
or defined. The substances called potash and soda 
are termed alkalies. They are said to have alkaline 
