12 AMERICAN MINERAL WATERS. 



[Fe(HCO 3 ) 2 ]. These bicarbonates, especially the calcium and mag- 

 nesium salts, are the constituents which produce that characteristic 

 of waters known as hardness. If such waters are boiled the bicar- 

 bonates are decomposed, the carbon dioxid passing off, the less 

 soluble normal carbonate being precipitated according to the following 

 equation : Ca(HCO 3 ) 2 = CaCO 3 + CO 2 + H 2 0. 



The iron and magnesium bicarbonates are similarly decomposed by 

 boiling. The normal magnesium salt, however, being much more 

 soluble than the corresponding calcium salt, the magnesium can not 

 be so completely removed from solution by the decomposition and 

 precipitation. Waters containing these bicarbonates which are 

 decomposed by boiling are said to be temporarily hard as distin- 

 guished from waters containing other salts of calcium and magne- 

 sium, as for instance, the sulphates, chlorids, and nitrates, which can 

 not be decomposed and removed by boiling. For this reason waters 

 containing the latter salts are said to be permanently hard. 



Solution of readily soluble mineral matter without an accompanying 

 chemical decomposition is also a large factor in determining the char- 

 acter of mineral waters. Thus when water in its passage through 

 the earth comes in contact with strata of such readily soluble material 

 deposited in some former geologic era it may become saturated with 

 such salts. As the salinity of the water in its passage through the 

 rocks is increased its solvent power for certain minerals is also in- 

 creased, and often a substitution occurs, the water taking up certain 

 mineral constituents and depositing some of the mineral matter 

 already held in solution. 



Even after the water has become more or less mineralized, further 

 changes due to both chemical and physical agencies may alter its 

 character. Lefort, in discussing the subject, says: " Mineral waters 

 when they are exposed to contact with air suffer a modification or 

 alteration which has a cause exclusively chemical or both mechanical 

 and chemical. Certain minerals, among them bicarbonates, have a 

 tendency to lose carbon dioxid; therefore, some salts, no longer pro- 

 tected by the great excess of gases which existed in the mineral water 

 in the state of oversaturation and being by nature easily altered, 

 absorb one of the elements of the air (oxygen) and become completely 

 modified." As examples of these two classes of change, may be 

 mentioned the decomposition of ferrous bicarbonate and the changes 

 produced in waters containing the sulphur compounds. 



Another important factor involved in the change of the mineral 

 character of a water is a change in pressure. The solubility of gases 

 in water increases with pressure, which in some cases affects the 

 solubility of certain salts. It follows, therefore, that water charged 

 to supersaturation with a gas may undergo a marked transfor- 

 mation when the gas is released either by the water issuing at the 



