CHAPTER XVI 

 COMMON COMPOUNDS OF OTHER ELEMENTS 



Classes of Compounds. In this chapter we shall deal 

 only with a few classes of compounds whose names are 

 in quite common use. We have already used the terms 

 oxide and acid a number of times in this book. These 

 are two of the four large classes of compounds. The 

 other two are bases and salts. 



Oxides. Because of its importance we are accustomed 

 in our preliminary study of oxygen to think that most of 

 it is in the air, but we soon learn that this is not the case. 

 Eight ninths of the weight of water is oxygen, but even 

 water contains but a small part of the total amount of 

 oxygen in the earth. Water is an oxide as is carbon 

 dioxide. Oxygen unites with many elements to form 

 oxides. 



Acids. An acid is a hydrogen compound whose dilute 

 water solution usually has a sour taste. It turns a blue 

 litmus solution red. Litmus is a blue dye which is ob- 

 tained from a kind of moss. It readily dissolves in water, 

 and when a drop of acid is added to the resulting blue 

 liquid, the color changes to red. 



A number of acids react chemically with metals, giving 

 off hydrogen. For example, when hydrochloric acid and 

 zinc are brought together, zinc chloride is formed and large 

 quantities of hydrogen are produced. Copper vessels 

 should not be used for cooking foods which contain acids, 

 even though they may be very inactive acids, since 



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