WATER. 107 



frothy sud or lather with a small quantity of soap, the lime or 

 magnesia which has made the water hard has used up — i.e., 

 has wasted — the soap or part of it. 



How may soft water be made hard ? By adding an 

 extremely small percentage of lime to it. . 



How can hard water be made soft? By boiling it. This 

 can be proved by the soap test. The reason is too difficult to 

 be taught experimentally in this grade. The lime in hard 

 water is held in solution by free carbonic dioxide ; the heat 

 drives this gas off and the lime settles to the bottom of the 

 kettle. Water can be softened chemically and strangely 

 enough one method is to add more lime, enough to use up the 

 free C0 2 and then all the lime is precipitated. 



Why is water in the lakes and rivers softer than what is in 

 the wells? (Well-water where there is no limestone is not 

 usually hard.) 



How comes the well-water to be so clear ? Try to construct 

 a filter of sand and earth and crushed charcoal. Put in turbid 

 or chalk-whitened water and catch the clear filtrate. 



Uses of Water. — What are the uses of water in the house- 

 hold, on the farm, and in the factory ? 



How is mankind served by water in the ocean, in the lake, 

 in the river ; by falling water, running water, still water ? 



For what purposes is the solid form particularly useful? 

 The gaseous form? 



Why cannot plants and animals live without water ? 



What is meant by the old saying that water and fire are 

 man's good friends but bad enemies. 



Potable Waters. — Why should drinking water be pure and 

 clean ? 



Waters that are " riley," discolored or possessed of taste or 

 smell, are not always or necessarily unwholesome. Waters 



