SPRING-WATER. 53 



impurities are left behind, and accordingly condensed 

 steam is perfectly pure water; there are numerous 

 contrivances for thus purifying water. The common 

 still, which consists of a vessel to generate steam in, 

 and a pipe, passing through a tub of cold water, to 

 condense the steam, is a familiar example. 



74. This explains why rain-water is much purer 

 than other sorts of water, because when the heat of 

 the sun evaporates water from the surface of the 

 earth, all the impurities which it contains are left 

 behind; and of course when this vapor is cooled and 

 falls down in the form of rain, it must be very nearly 

 pure. 



75. Springs, which rise from the ground, always 

 contain earthy matters dissolved in them, which vary 

 in nature and quantity, with the soil through which 

 the springs rise. The presence of these impurities 

 in water in any quantity gives to it that peculiar* 

 character which is termed hardness. Sometimes 

 springs contain a small quantity of iron or sulphur, 

 and other substances, which constitute the many 

 varieties of mineral waters. These matters, like the 

 more common earthy impurities, are all derived 

 from the beds of stone, sand, or clay, through which 

 the springs rise; because the source of all springs is 

 rain-water, which, falling pure from the clouds, 

 becomes contaminated by filtering through the earth, 

 and collects in holes and cavities, or porous beds 

 of sand, constituting springs and wells. 



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