IX.] CHEMISTRY OF NATURAL WATERS. 139 



together with, chloride of magnesium, but is precipitated by 

 ebullition. (Amer. Jour. Science (2), XXVII. 173.) 



55. Bicarbonate of magnesia and chloride of calcium, when 

 brought together in solution, undergo mutual decomposition 

 with separation of carbonate of lime, if the solutions are not 

 too dilute. At the ordinary temperature and pressure, water 

 saturated with carbonic acid will not hold more than about one 

 gramme of carbonate of lime to the litre (1 : 1,000), equal to 

 only 0.88 grammes of carbonate of magnesia. (The solubility 

 of carbonate of lime in pure water is well known to be much less, 

 and is, according to Bineau, equal to 1 : 30,000 or 1 : 50,000.) 

 We should not, therefore, expect to find that water holding 

 chloride of calcium in solution would yield, by boiling, more 

 than the latter amount of magnesian carbonate ; so much might 

 evidently be formed by the action of dissolved carbonate of 

 lime which the water might hold as bicarbonate. I have else- 

 where described a series of experiments on the solubility of 

 bicarbonate of lime both in pure water and in saline solutions, 

 and have shown that the presence of salts of soda, lime, and 

 magnesia does not increase the amount of bicarbonate of lime 



which water is capable of holding permanently in solution 



Recent experiments have, however, shown me that supersatu- 

 rated solutions of a certain stability may be obtained, in which 

 comparatively large quantities of neutral carbonates of lime 

 and magnesia exist in the presence of sulphates and chlorides 

 of calcium and magnesium. 



56. In a memoir on the salts of lime and magnesia pub- 

 lished in 1859 (Amer. Jour. Science (2), XXVIII. 171), it 

 was shown that by the addition of bicarbonate of soda to a 

 solution holding chlorides of sodium, calcium and magnesium, 

 with or without sulphate of soda, and saturated with carbonic 

 acid, it is possible to obtain transparent solutions holding from 

 3.40 to 4.16 grammes of carbonate of lime to the litre. Of 

 this, however, the greater part was deposited after twenty- 

 four hours, when the solutions were found to contain some- 

 what less than 1.0 gramme, in the form of bicarbonate. Bou- 

 tron and Boudet had previously shown that by saturating lime- 



