138 CHEMISTRY OF NATURAL WATERS. [IX. 



rine and the carbonic acid that chloride of calcium, chloride of 

 magnesium, bicarbonate of lime, and bicarbonate of magnesia 

 coexist. When such a solution is submitted to evaporation 

 at ordinary temperatures, provided there is present a sufficient 

 amount of chloride of calcium, carbonate of lime alone is de- 

 posited, and chloride of magnesium remains in solution. In 

 case the chloride of calcium is insufficient, the lime is still first 

 deposited as carbonate, and the more soluble magnesian car- 

 bonate is precipitated by further evaporation. When, how- 

 ever, such a water is boiled, a reverse process takes place, 

 the carbonate of lime slowly decomposes the magnesian chlo- 

 ride, and carbonate of magnesia is deposited, while chloride 

 of calcium remains in solution. Hence if the amount of chlo- 

 ride of magnesium be great enough, and the ebullition suffi- 

 ciently prolonged, the precipitate will at length contain only 

 carbonate of magnesia ; while an equivalent of chloride of cal- 

 cium, now found in the solution, represents the carbonate of 

 lime which the analysis of the precipitate at an earlier stage 

 of the ebullition would have furnished. 



As an example of this may be cited the analysis of a water 

 of Class II. from Ste. Genevieve, where the precipitate, after 

 a few minutes' boiling, contained carbonates of lime and mag- 

 nesia in the proportion 12 : 750. When, however, another 

 portion was boiled down to one sixth, the precipitate was 

 found to be pure carbonate of magnesia. The water of another 

 spring of the same class, that of Plantagenet, [described in the 

 original paper,] gave as the result of ebullition a precipitate 

 of .8904 of carbonate of magnesia and .0330 of carbonate of 

 lime ; while the liquid retained a portion of lime equal to .1364 

 of chloride of calcium, besides .2452 of chloride of magnesium, 

 in 1,000 parts. When, however, this water 'is left to spon- 

 taneous evaporation, the whole of the lime separates as carbon- 

 ate, and the liquid remains for a time charged with carbonate 

 of magnesia, probably as sesqui-carbonate. This solution is, 

 however, after a time spontaneously decomposed even in closed 

 vessels, with deposition of a portion of crystalline hydrated 

 carbonate of magnesia ; another portion remains in solution, 



