CHAPTER XIV 

 ELEMENTS, COMPOUNDS, AND MIXTURES 



Interrelation of the Sciences. The different branches 

 of science, such as physics, chemistry, biology, physical 

 geography, and botany, are not separated by any very 

 definite boundaries, as we shall see. In the study of phys- 

 ical geography we must know something of the other 

 sciences in order to understand the changes that have 

 occurred and are occurring in the life of the earth. 

 Weathering depends upon both physical and chemical 

 changes. Winds are caused by heat, a physical agent. 

 A study of plants and animals involves the study of nu- 

 merous physical and chemical changes. So we could go 

 on citing example after example of the ways in which the 

 sciences interlock and are dependent upon one another. 



How matter is changed. We may change most 

 substances in many ways. If we apply heat to a 

 piece of iron, it becomes hot ; as more heat is applied it 

 becomes red hot and gives off light. If the heating con- 

 tinues, the iron finally melts and may be poured into a 

 different form. As the liquid iron cools it passes back 

 through these various changes and finally becomes a cold, 

 black piece of iron again. A piece of iron, when rubbed 

 with a magnet, itself becomes a magnet and exhibits the 

 property of attracting pieces of iron and steel. After a 

 time the magnetism is lost. Through these various 

 changes the iron has never ceased to be iron. 



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