298 Common Science 



element iodine. (The iodine you use when you get 

 scratched is the element iodine dissolved in alcohol.) 

 It is not necessary for you to remember the chemical 

 symbols unless you mean to become a chemist or unless 

 you read a good deal about chemistry. But almost 

 every one knows at least that H means hydrogen, O 

 means oxygen, and C means carbon. 



When a chemist wants to show that water is made of 

 hydrogen two parts and oxygen one part, he writes it 

 very quickly like this : H 2 O (pronounced " H two O "). 

 " H 2 O " means to a chemist just as much as " w-a-t-e-r " 

 means to you ; and it means even more, because it tells 

 that water is made of two parts hydrogen and one part 

 oxygen. If a chemist wanted to write, " You can take 

 water apart and it will give you two parts of hydrogen and 

 also one part of oxygen," this is what he would put down : 



If he wanted to show that you could combine two parts 

 of hydrogen and one part of oxygen to form water, he 

 would write it quickly like this : 



These are called chemical equations. You do not need 

 to remember them; they are put here merely so that 

 you will know what they look like. Some of them are 

 much longer and more complicated, like this : 



HC 2 H3O 2 +NaHC0 3 -^H 2 + CO 2 +NaC 2 H 3 O 2 . 



This is the chemist's way of saying, " Vinegar is made of 

 one part of hydrogen gas that will come off easily and 

 that gives it its sour taste, two parts of carbon, three 

 parts of hydrogen that does not come off so easily, 



