152 CHEMISTRY OF NATURAL WATERS. [IX. 



hydrochloric solution of this precipitate became gelatinous dur- 

 ing evaporation. The water thus evaporated still retained in 

 solution, besides a portion of lime, .064 of silica ; which was 

 completely separated when the alkaline liquid was evaporated 

 to dryness in contact with the earthy carbonates previously 

 precipitated. When, however, these were removed by nitration, 

 it was found that during the evaporation to dryness a reaction 

 took place by which the precipitated silicate of lime was par- 

 tially decomposed, the separated silica being redissolved by the 

 alkaline carbonate. In the case of the Chambly water in 1852, 

 which contained in 1,000 parts .073 of silica, .042 parts still 

 remained in solution in the water evaporated to one twentieth ; 

 and in that of the Ottawa Eiver when reduced to one fortieth 

 there still remained in solution from 10,000 parts of water, 

 .075 of silica and .028 of lime. Similar results were observed 

 with the alkaline-saline waters of Varennes and Fitzroy, and 

 all of these yielded, by further evaporation, precipitates con- 

 taining silica and lime, and in one instance magnesia. 



It is not, however, probably from alkaline waters like these, 

 but from neutral sea-water, that the silicates of magnesia (and 

 of lime), which abound in stratified rocks, have been for the 

 most part formed. See further on this point, 41. 



71. ORGANIC MATTERS. In 44 we have described some 

 of the reactions of the organic matter found in the Chambly 

 water, and it is to be remarked that small portions of a similar 

 substance were found in all alkaline waters of the third and 

 fourth classes, and caused them to become brownish when 

 evaporated to a small volume. This, it has been already sug- 

 gested, may have a superficial origin, the organic matters car- 

 ried down by surface-waters being kept in solution by the 

 alkaline salts ; it is not, however, impossible that this same 

 menstruum may remove the organic matters which abound in 

 the pyroschists and other materials of organic origin in the 

 ancient rocks. Thus, for example, the coprolites of the lower 

 paleozoic limestones contain so much animal matter as to evolve 

 an odor like burning horn when exposed to heat. (Geology of 

 Canada, 462.) 



