LIQUIDS. 303 



dicial because it is too hard, or because it is too soft; and they may 

 relieve their ailments simply by removing to a neighborhood where 

 they can drink a different water. 



"Water now and then contains metals like iron, lead and copper. 

 It ought not to be drunk if there be more than one-tenth of a grain 

 of iron or copper in a gallon of water. A very minute proportion 

 of lead is injurious. 



RAIN-WATER is soft, and naturally contains the smallest amount 

 of solid impurity; but unless carefully collected in specially clean 

 vessels in the open country, and then covered, it is likely to become 

 impure. If the atmosphere be impregnated with smoke from 

 crowded dwellings or fumes from chemical and other factories, it can- 

 not be relied on for purity. If, however, it fall through a pure 

 atmosphere it may be contaminated with what has accumulated on 

 housetops and in water-pipes, and if collected from the roofs of 

 houses and stored in underground tanks, is often polluted to a dan- 

 gerous extent. It is therefore rarely in a fit state for drinking, 

 though it may be very useful for domestic purposes. Its freedom 

 from earthy salts, moreover, renders it liable to contamination from 

 leaden pipes if it should be brought through them. But so beneficial 

 are its effects upon the skin, that an exclusive use of rain-water for 

 washing would greatly modify, if not entire remove many skin- 

 diseases. 



SPRING-WATER is rain-water which has percolated through the 

 earth, and acquired saline elements from the soil through which it 

 has passed. Chalybeate and other mineral waters are thus charged 

 and to such a degree as to render them unsuitable for ordinary 

 drinking or culinary purposes. They should be taken only when 

 prescribed as medical agents. 



It is a fallacy to suppose that surface-well water is purer than 

 that obtained from deep wells, because it is more sparkling and often 

 cooler and clearer. The sparkling of these waters is due to the 

 presence of carbonic-acid gas, and that acid is derived from the de- 

 composition of animal and vegetable substances. 



WELL- WATER is collected spring- water. If the well be deep, 

 and there is no leakage into it from some higher layer of soil, or 

 from some neighboring decaying animal or vegetable matters, it 

 usually affords a safe and wholesome drink. Some of the purest 

 water is obtained from deep wells. Of the different varieties of drink- 

 able water the best for dietetic purposes are deep spring and well- 

 waters. Superficial well-water, however clear, bright and tasteless, 

 should be regarded with suspicion, for it is frequently saturated with 

 leakage or soakage from privies, drains or cesspools, often covered up 

 and unknown. W'ater collected from uncultivated land and allowed 

 to subside in reservoirs, or filtered through sand, constitutes good 

 water for domestic purposes; but water collected from the surface 

 or drains of cultivated land is always more or less polluted with 

 organic matter, even after subsidence in lakes or reservoirs and 



