HYDROLOGY. 117 



third, sulphureous ; fourth, chalybeate. loduretted, Bromu- 

 retted, and acid waters are by some writers added to these 

 classes. Still further defined, they stand thus : 



FIRST. 



The acidulous waters contain and evolve gases, principally 

 carbonic acid, making them pungent to the taste and spark- 

 ling. They hold in solution saline substances, mostly car- 

 bonates of lime, magnesia, soda, and iron, with common 

 salt. 



SECOND. 



Saline waters abound in salts, sulphate of magnesia or 

 Epsom salts, sulphate of soda or Glauber salts, the medi- 

 cinal properties of which are well known to all. Chloride 

 of sodium or common salt, and carbonic acid are sometimes 

 found in them. 



THIRD. 



The sulphureous, which are characterized by a gas charged 

 with sulphur, called sulphuretted hydrogen, or sulphohydric 

 acid gas. The presence of this gas is recognized by well- 

 known and familiar tests. This class is again subdivided 

 into those waters which contain free sulphuretted hydrogen 

 gas, those which contain carbonic acid or acidulo-sulphure- 

 ous and those which contain carbonic acid and sulphuretted 

 hydrogen, and those also which contain iron with other 

 sulphureous combinations. 



FOURTH. 



This class embraces the chalybeate or ferruginous waters. 

 The iron in most of these waters is in a state of a carbonate 

 of protoxide dissolved in carbonic acid. They also contain 

 the sulphate of iron, or common copperas. 



The medicinal qualities of these waters are of course 

 the therapeutic properties of iron in general. There is 

 another division of waters into cold, and thermal or heated. 

 All the four classes of mineralized waters are found in either 



