122 CHEMISTRY OF NATURAL WATERS. [IX. 



The analyses of European waters furnish comparatively few ex- 

 amples of the predominance of earthy chlorides.* 



41. We have already shown in 38 how the action of 

 carbonate of soda upon sea-water or bittern will destroy the 

 normal proportion between the chlorides of magnesium and 

 calcium by converting the latter into an insoluble carbonate, 

 and leaving at last only salts of sodium and magnesium in 

 solution. A process the reverse of this has evidently inter- 

 vened for the production of waters like that from Cape Breton, 

 and some others noticed by Lersch, in which chloride of cal- 

 cium abounds, with little or no sulphate or chloride of magne- 

 sium. This process is probably one connected with the forma- 

 tion of a silicate of magnesia. Bischof has already insisted 

 upon the sparing solubility of this silicate, and has asserted 

 that silicates of alumina, both artificial and natural, when 

 digested with a solution of magnesian cliloride, exchange a por- 

 tion of their base for magnesia, thus giving rise to solutions of 

 alumina; which, being decomposed by carbonates, may have 

 been the source of many of the aluminous deposits referred to in 

 9. He also observed a similar decomposition between a solu- 

 tion of an artificial silicate of lime and soluble magnesian salts. 

 (Bischof, Chem. Geology, I. 13 ; also Chap. XXIV.) In repeat- 

 ing and extending his experiments, I have confirmed his obser- 

 vation that a solution of silicate of lime precipitates silicate of 

 magnesia from the sulphate and the chloride of magnesium ; 

 and have moreover found that by digestion at ordinary temper- 

 atures with an excess of freshly precipitated silicate of lime, 

 chloride of magnesium is completely decomposed ; an insoluble 

 silicate of magnesia being formed, while nothing but chloride 

 of calcium remains in solution. It is clear that the greater 

 insolubility of the magnesian silicate, as compared with silicate 

 of lime, determines a result the very reverse of that produced by 

 carbonates with solutions of the two earthy bases. In the one 



* Lersch, Hydro-Chemie, Zweite Auflage : Berlin, 1864; vide p. 207. This 

 excellent work, which is a treatise on the chemistry of natural waters, in one 

 volume 8vo of 700 pages, was unknown to me when I prepared the first part 

 of this essay. 



