ACIDS, BASES, AND SALTS ; NEUTBALIZATIOK 23 



chemical elements, hydrogen is also noteworthy as being 

 the lightest chemical element known. 



Metallic elements. — All the elements we have con- 

 sidered so far are called by chemists, nonmetals, to distin- 

 guish them from another group of elements called metals. 

 Some of these metallic elements are very familiar to us 

 under the names of iron, zinc, copper, gold, etc. Beside 

 these more familiar metals, thei-e are others that form 

 important parts of our bodies but which very rarely occur 

 uncombined owing to their greater affinity. Such are the 

 elements calcium, potassium, sodium, and magnesium. 

 The most important characteristic of metals is that when 

 they combine, it is with a nonmetallic element, and very 

 rarely with another metal. Such compounds of metals 

 and nonmetals fall very readily under two classes, bases, 

 and salts. All chemical elements are divisible into metals 

 and nonmetals. 



Acids, bases, and salts; neutralization. — When iron is 

 exposed to the air it takes on a reddish coating that we call 

 rust. This action is hastened by the presence of moisture. 

 This rust is merely a compound of the metal iron with 

 the oxygen of the air or water. Similarly other metals 

 such as potassium, sodium, and calcium, etc., are able to 

 unite with the oxygen of air or water and form oxides. 

 If we dissolve some of these latter oxides in water the 

 mixtures have peculiar properties. They have a slippery 

 feel and a soapy taste, and when we put into them a piece 

 of paper dyed red with the vegetable coloring matter, litmus, 

 they change the color of the paper from red to blue. Such 

 mixtures are not solutions but true chemical compounds 

 of the oxides and the water, and are called bases. If 

 we put the paper which was colored blue by these bases 



