HYDROGEN. 71 



The waters of springs, wells, rivers, etc., differ widely from 

 each other; they all contain more or less of substances dissolved 

 by the water in its course through the atmosphere or through 

 the soil and rocks. The constituents thus absorbed by the 

 water, are either solids or gases. 



Solids generally found in natural waters, are common salt 

 (sodium chloride), gypsum (calcium sulphate), and carbonate of 

 lime (calcium carbonate); frequently found are chlorides and 

 sulphates of potassium and magnesium, traces of silica and 

 salts of iron. The gases absorbed by the water are chiefly con- 

 stituents of the atmospheric air, oxygen, nitrogen, and carbon 

 dioxide. One hundred volumes of water contain about two 

 volumes of nitrogen, one volume of oxygen, and one volume of 

 carbon dioxide. 



Mineral waters are spring waters, containing one or more sub- 

 stances in such quantities that they impart to the water a pecu- 

 liar taste and generally a decided medicinal action. According 

 to the predominating constituents we distinguish bitter waters, 

 containing larger quantities of magnesium salts; iron waters, 

 containing carbonate of iron; hepatic waters, containing sul- 

 phuretted hydrogen; acidulous waters, containing larger quan- 

 tities of carbonic acid, etc. 



Drinking water. A good drinking water should neither be 

 an absolutely pure water, nor a water containing too much of 

 foreign matter. "Water containing from 1 to 3 parts of total 

 solids (chiefly carbonate of lime and common salt) in 10,000 

 parts of water and about 1 volume of carbon dioxide in 100 

 volumes of water, may be said to be a good drinking water. 

 There are, however, good drinking waters which contain more 

 of total solids than the amount mentioned above. 



Most objectionable in drinking water are organic substances, 

 especially when derived from animal matter and in a state of 

 decomposition. The presence of organic matter in water may 

 be demonstrated by evaporating about one litre of it in a small 

 porcelain or platinum dish over a steam bath. The residue left 

 represents the total solids, and is generally of a white color. 

 If this residue, upon being further heated over a flame, turns 

 black (by separation of carbon), the presence of organic matter 

 is indicated. 



