CHAPTER XVII 



WATER 



( Water = H 2 0) 



Introduction. Of all substances on the surface of the 

 earth, water is by far the most abundant. 



In the liquid form it makes up the oceans, lakes, seas, 

 rivers, springs, and brooks, while the air holds vast 

 quantities of it in the gaseous form. Add to this the 

 vast stretches of ice and snow of the polar regions, and 

 one soon realizes the truth of the statement, " three- 

 fourths of the earth's surface is covered with water." 



Composition. For a long time water was regarded 

 as an element. However, toward the close of the 

 eighteenth century it was proved to be a compound of 

 the two elements, hydrogen and oxygen. 



This can be shown in two ways. First, by breaking 

 up the compound into its elements with the electric cur- 

 rent; and, second, by combining the two elements by 

 ignition. 



Take an electrolysis apparatus, such as is shown in 

 Figure 42, and fill the burettes with water containing a 

 small amount of sulphuric acid. Each arm of the appa- 

 ratus holding the burette is closed at the bottom with 

 a rubber stopper, through which passes a glass tube 



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