CHAPTER XV 

 DRINKING WATER 



216. Pure water. Water is the only food which man 

 habitually takes without its previous preparation. Water 

 is the same from whatever source, but substances dissolved 

 in the water change its appearance. Carbonic acid gas, 

 oxygen, and air are dissolved in all ordinary water, and in 

 it float particles of dust and often a few harmless living 

 germs. Such water is clear and colorless. It has a slight 

 taste, due to the dissolved air. When the air is expelled 

 by boiling, the water is insipid and almost tasteless. 



217. Hard and soft water. Water also contains a vari- 

 able amount of mineral matter, especially lime, soda, and 

 potash. Water containing lime makes the fingers feel 

 slightly rough and puckered. The lime combines with 

 soap, forming a scum which will not dissolve. Water con- 

 taining lime is said to be hard, while water with little or no 

 lime is soft. Although some gases and minerals are dis- 

 solved in all water, they are harmless and do not make it 

 impure, but rather they give it a more pleasant taste. 

 When very hard water is boiled, some of the lime is 

 deposited on the sides of the kettle, and the water is 

 improved but not made soft. 



218. Mineral waters. When much mineral matter is present 

 the water is called mineral water. The principal minerals thus found 

 in water are salt, lime, soda, potash, iron, and sulphur. These waters 

 form springs in various parts of the country, and have borne a great 



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