22 CHEMISTRY, GEOLOGY 



MAGNESIA. You have seen the magnesia 

 sold by the druggists, or in the shops. It is in 

 lumps, very white and powdery. In that state 

 it is called carbonate of magnesia. It has a 

 metallic base, called magnesium. When carbon- 

 ate of magnesia is burned where the air cannot 

 get at it. it is called calcined magnesia. There 

 is a kind of limestone called MagHesian, from 

 which magnesia is procured. It is also obtained 

 from sea- water. Magnesia is a very mild alkali. 

 All the alkalies, when mixed with acids, combine 

 with them, arid make what are called salts. In 

 the act of uniting, the mixture froths up, and 

 looks as though it was boiling. This boiling up 

 and frothing is called effervescence. 



IRON is a well-known metal. It is the most 

 useful of all the metals. It is found in the earth, 

 and is called iron ore. Iron is obtained by 

 smelting the ore in large and very hot furnaces. 

 Steel is iron combined with carbon. Iron is a 

 soft metal, steel is very hard. Iron is ductile, 



Questions. What do you know about magnesia ? What 

 is calcined magnesia ? What is it obtained from ? What is 

 its metallic base called ? What do the alkalies do when mixed 

 with acids ? What is the frothing up called ? Can you tell 

 me anything about iron ? Where is iron found ? How is it 

 obtained ? 



