148 CHEMISTRY OF NATURAL WATERS. [IX. 



such that only .191 of carbonic acid, or just about one third 

 of the carbonic acid present, is required for the neutral car- 

 bonate. Nor is this change due entirely to a less amount of 

 carbonate of soda; the carbonates of lime and magnesia in 

 1847 required .246, and in 1865 only .153, of carbonic acid. 

 The changed conditions which we here meet with may be ex- 

 plained by supposing that the carbonated bases are due to the 

 mingling in different proportions of neutral carbonate of soda 

 (generated by the reaction indicated in 13) with an earthy- 

 saline water holding a constant amount of free carbonic acid ; 

 which, in some cases, is more than is required to form bicar- 

 bonates, but in others, as we have seen above, shows a de- 

 ficiency. 



66. If we admit, as I have already assumed, that the 

 waters of the second and third classes have been generated by 

 the mingling of solutions of carbonate of soda with waters of 

 the first class, it can readily be shown that these solutions 

 contained chiefly or exclusively the neutral carbonate. If we 

 add a solution of bicarbonate of soda to earthy-saline waters 

 of the first class, it is easy to obtain solutions holding twenty 

 grammes or more of bicarbonate of magnesia to the litre ; while 

 in none of the natural waters of the second class do our anal- 

 yses show the existence of much over one gramme to the litre. 

 Again, if we suppose any considerable amount of chloride of 

 calcium to be decomposed by bicarbonate of soda, the separa- 

 tion of the lime in the form of neutral carbonate, and the 

 liberation of the second equivalent of carbonic acid, would 

 yield waters holding an excess of carbonic acid above that 

 required to form the bicarbonates of the solution. From the 

 absence of such an excess, as appears in the case of the waters of 

 Caledonia, Varennes, and St. Leon, and from the small amount 

 of bicarbonate of magnesia in these waters, it may be concluded 

 that the alkaline salt whose addition has changed their charac- 

 ter was the neutral carbonate of soda. 



67. Examples are not wanting of waters in which, as in 

 those of Caledonia in 1847, the carbonic acid is insufficient to 

 form bicarbonates (or even neutral carbonates) with the bases 





