244 Composiiion of the Waters of the St. Lawrence and Ottawa. 



nesia with the formation of a very insoluble magnesian silicate ; 

 and I have found that by boiling the artificial hydrocarbonate of 

 magnesia with a solution of silicate of soda, this salt may be 

 completely decomposed with the formation of carbonate of soda 

 and an insoluble silicate of magnesia which gelatinizes with 

 acids*. 



We may then suppose in the recent mineral waters the pre- 

 sence of silicates and bicarbonates of soda, lime and magnesia ; 

 but on boiling, the earthy carbonates are precipitated (witli some 

 silicate), while the dissolved silicates of lime and soda are slowly 

 decomposed as the liquid evaporates by the carbonate of mag- 

 nesia, with formation of carbonates of soda and lime, and silicate 

 of magnesia, until the whole of the silicic acid is removed from 

 the solution. The organic acids of the river- waters do not play 

 any important part in these reactions, for the same phenomena 

 are observed in the waters of alkaline springs which contain only 

 insignificant traces of organic matters. It is worthy of remark, 

 that in these waters the amount of carbonic acid is not nearly 

 sufficient to form bicarbonates with the lime, magnesia, and soda 

 uncombined with sulphuric acid or chlorine. And I have sug- 

 gested, in my analysis of the Caledonia springs, that the mag- 

 nesia and soda are present as a double carbonate, whose existence 

 in a dilute solution seems compatible with a dissolved silicatef. 



The comparison of the two river-waters whose analysis we 

 have just given, shows the following differences : — The water of 

 the Ottawa, containing little more than one-third as much solid 

 matter as the St. Lawrence, is impregnated with a much larger 

 proportion of organic matter derived from vegetable decomposi- 

 tion, and a larger amount of alkalies uncombined with chlorine 

 or sulphuric acid. Of the alkalies in the state of chlorides, the 

 potassium salt in the Ottawa constitutes 32 per cent., and in the 

 St. Lawrence oialy 15 per cent, j while in the former the sihca 

 equals 34, and in the latter 23 per cent, of the ignited residue. 



The Ottawa river drains a region of crystalline rocks, and the 

 alkaUes liberated by the decomposition of the felspars of these 

 rocks give their character to its waters ; the extensive vegetable 

 decomposition evidenced by the organic matters in solution must 

 also contribute a portion of potash ; while the basins of the great 

 lakes through which the St. Lawrence flows are excavated in 

 palfeozoic strata M'hich abound in limestones rich in salt and 

 gypsum, and have given to the water of this river that predomi- 



* See also Kulilmann, Comptes Rendus de VAcad. December 3, 1855, 

 p 981, "On the Decomposition of Alkaline Silicates by Chalk." 



t Geological Siirvev Report, 1848, pp. 14(i, 147. Ditto, 1851, p. 52. 

 Ditto, 1852, p. 115. Ditto, 1853, p. 155. Also Comptes Rendus de VAcad. 

 August 20, 1856. 



