154 WATER 



Alum, even in minute amount, clears turbid water. Oxida- 

 tion gradually destroys disagreeable or dangerous foulness ; 

 hence a running stream, contaminated even by sewage 

 several hundred yards higher up, may again become clear 

 and wholesome. Alkaline permanganates, by similar oxida- 

 tion, promptly destroy organic contamination. Boiling 

 destroys most noxious living vegetable and animal matters, 

 drives off carbonic acid gas, and thus throws down calcium 

 carbonate, the cause of temporary hardness. Sodium car- 

 bonate, or lime, as in Clarke's process, diffused through hard 

 water, which is then allowed to settle, abstracts carbonic 

 acid gas, and causes subsidence of calcium and magnesium 

 carbonates, and also reduces the permanent hardness pro- 

 duced by calcium sulphate. For chemical and pharma- 

 ceutical purposes, aqua destillata is requisite, and distillation 

 leaves behind all impurities except a trace of organic 

 matters, and one to two per cent, per volume of air. Such 

 distilled or other pure water is understood to be used when 

 * water ' is ordered in prescriptions. 



Mineral waters are unfit for general use on account of 

 their undue proportion of mineral matters or gases, or from 

 their being at a higher temperature than that of the locality 

 in which they are found. The most common mineral waters 

 are those containing iron and salines. Sea water has a 

 specific gravity of 1027 ; i,n imperial pint contains about 

 312 grains of solid matters, of \vhich about 240 grains are 

 common salt. 



ACTIONS AND USES. Water is nutrient, diluent, anti- 

 pyretic, diuretic, and detergent. Introduced into the body 

 in excess of its requirements, it is removed usually within 

 six hours, chiefly by the kidneys, and in less amount by the 

 skin and bowels. When given cold, the kidneys perform 

 the main excretory office ; but when used hot, water is an 

 adjuvant diaphoretic, cathartic, and (warm) in dogs and 

 other carnivora, an emetic. Water applied topically, as in 

 the form of hot fomentation, or the familiar warm-compress, 

 is emollient and anodyne, abates congestion of circum- 

 scribed inflammation and wounds, and its beneficial effects 

 are also reflexly propagated to adjacent parts. At high 

 temperatures water is an irritant, but dry steam mixed with 



