T. S. Hunt on the Chemistry of Natural Waters, 49 
mal proportion between the chlorids of magnesium and cal- 
cium 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 intervened for the 
gioduction of waters like that from Cape Breton and some 
others noticed by Lersch, in which chlorid of calcium abounds, 
with little or no sulphate or chlorid of magnesium. This pro- 
cess is probably one connected with the formation of a silicate 
of magnesia. Bischof has already insisted upon the sparing 
solubility of this silicate, and he observed that silicates of 
alumina, both artificial and natural, when digested with a solu- 
tion of magnesian chlorid, exchange a portion of their base for 
magnesia, thus giving rise to solutions of alumina; which, being 
decomposed by carbonates, may have been the source of man 
of the aluminous deposits referred to in $9. He also observed 
a similar decomposition between the solution of an artificial sil- 
icate of lime and soluble magnesian salts. (Bischof, Chem. Ge- 
silicate of lime precipitates silicate of magnesia from the sulphate 
and the chlorid of magnesium; and have found, moreover, that 
by digestion at ordinar temperatures with an excess of freshly 
precipitated silicate of lime, chlorid of magnesium is completely 
ecomposed ; an insoluble ‘silicate of magnesia bein ng formed, 
while nothing but chlorid of calcium remains in solution. - It i is 
clear that the greater insolubility of the magnesian silicate, as 
com with silicate of lime, determines a result the very re- 
verse of that produced by carbonates with solutions of the two 
n the one case, the lime is separated as carbon- 
ate, the magnesia remaining in solution; while in the other, by 
the action of silicate of soda (or of lime), the magnesia is re- 
moved and the lime remains. Hence, carbonate of lime and sil- 
icate of magnesia are everywhere found in nature; while car- 
bonate of magnesia and silicate of lime are produced only under 
local and exceptional conditions. The detailed results of some 
experiments on this subject are reserved for another place. It 
is evident that the production from the waters of the early seas 
of sepiolite, tale, serpentine, and other rocks in which a 
magnesian silicate ‘abou nds, must, in closed basins, have given 
rise to waters in which chlorid of calcium would predominate. 
§ 42. Of the waters of the second class whose analyses are 
here given, the first three occur, with many others of similar 
ter, on the south side of the Ottawa river, below the city 
of that name. The remaining four are on the north side of the 
St. Lawrence, between Montreal and Quebec, where also similar 
waters abound. All of these springs rise from the Lower - Silu- 
rian limestones of the region. 
Am. Jour. Sci.—Seconp Serres, Vou. XL, No. 118.—Juny, 1865. 
7 
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