THE CHEMISTRY OF UNDERGROUND WATERS. 813 



THE CHEMISTRY OF UNDERGEOUND WATERS. 



Br Professor G. A. DAUBEEE, 



MEMBER OF THE FRENCH ACAUEIIY OF SCIENCES. 



TO understand the chemical composition of subterranean waters, 

 we must inquire anew of the geological constitution of the 

 coixntry, and it will usually answer with precision and certainty. 



Water does not have to remain long in the soil to dissolve and 

 remove various substances from the rocks. Chemical analysis has 

 already shown that such substances exist in the water-sheets of al- 

 luviums in more notable proportions than in the neighboring rivers. 

 The difference is sufficient to explain why in Hungary, Egypt, India, 

 and China, river-water is preferred to well-water for culinary uses. In 

 the subsoil of inhabited places, water is not charged with mineral sub- 

 stances only ; but the liquids of manure-heaps and other elements of 

 corruption are transmitted to it by sewers, factories, and cemeteries. 

 The unhealthy effect of the impurities thus conveyed to the wells has 

 been frequently recognized ; and it would be surprising if water ex- 

 posed for centuries to such infiltrations did not cease to be potable. 



The most common bodies found to be contained in subterranean 

 waters are oxygen, nitrogen, and carbonic-acid gases, chlorides, car- 

 bonates, silicates, and sulphates of lime, magnesia, and soda, and or- 

 ganic substances, in the pi'esence of excessive proportions of which 

 water may cease to be drinkable, or even fit for domestic uses. 



Water sometimes acquires also useful properties during its subter- 

 ranean course. Springs which are employed as therapeutic agents are 

 endowed with mineral qualities. The name of mineral is sometimes 

 extended to other springs the high temperature of which makes them 

 susceptible of similar uses, even when the amount of foreign matter 

 they contain is inferior to what is included in many potable waters. 



Chloride of sodium, or sea-salt, is sometimes present in so feeble 

 proportions as not to be perceptible to the taste. It is derived from 

 very widely distributed rocks, which contain traces of it. In other 

 springs it exists in much stronger proportions. Such springs derive 

 their salinity from beds of rock-salt, which it has been found jirofitable 

 to mine or bore for directly. 



Gypsum is dissolved in water under similar conditions. It is pres- 

 ent in large masses and in a very fine state of division in the Parisian 

 Tertiary beds, and, being freely soluble, gives hardness to many 

 springs. It is often associated with other substances, which give 

 therapeutic qualities to water, as in the cold springs of Contrexeville 

 and Vittel in the Vosges, and the hot springs at Agovie and Schinz- 

 nach in Baden. The mineralization in these cases is due to the presence 

 of the soluble sulphates of lime and magnesia, which are furnished by 



