1865.] CHEMISTRY OF NATURAL WATERS. 291 



these it appears that free soluble silica, when mingled with a 

 solution of bicarbonate of magnesia, or with the neutral carbonate 

 dissolved in sulphate of magnesia in the manner described in § 56, 

 whether separating immediately or by a slower process of gelatin iza- 

 tion, always carries down with it, in combination, a few hundredths 

 of magnesia. 



In these experiments, besides the carbonate of magnesia, sulphate 

 or chlorid of magnesium was present ; but the silicated natural waters 

 now under discussion are alkaline from the presence of carbonate of 

 soda, and whatever partition of bases between carbonic and silicic 

 acids may exist in the recent waters, we may suppose that when they 

 are boiled a silicate of soda is formed, with the expulsion of carbonic 

 acid. The silicate thus produced reacts on the earthy bases present 

 with the production of silicates of lime and magnesia, which are in 

 part precipitated with the earthy carbonates. Berzelius and 

 Kersten long since observed the separation of such silicates during 

 the evaporation of the waters of Carlsbad and of Marienbad 

 (Bischof. i, 5) ; while a silicate of lime is said to be deposited from the 

 waters of Wiesbaden. But the silicates thus formed are but 

 partially precipitated — a portion remaining in solution till a late 

 period of the evaporation. Dr. J. Lawrence Smith long since 

 remarked the existence of a dissolved silicate of lime, apparently 

 combined with soda, in the concentrated alkaline waters of Broosa 

 in Asia Minor. (Silliman's Journal [2], xii, 377.) 



Many facts in accordance with the above were observed in the 

 analyses of the waters described in this paper. Thus the water 

 of Belceil, which held in 10U0 parts .114 of silica, when evaporated 

 to one-tenth deposited with the carbonates .050 of silica, and the 

 hydrochloric solution of the precipitate became gelatinous during 

 evaporation. The solution still retained in solution, besides a portion 

 of lime, .064 of silica; which was completely separated when the alka- 

 line liquid was evaporated to dryness in contact with the earthy 

 carbonates previously precipitated. When however these were 

 removed by filtration it was found that during the evaporation to 

 dryness a reaction took place by which the precipitated silicate of 

 lime was partially decomposed, the separated silica bein<>- redis- 

 solved by the alkaline carbonate. In the case of the Chambly 

 water of 1852, which contained in 1000 parts .073 of silica, .042 

 parts still remained in solution in the water evaporated to one 

 twentieth ; and in that of the Ottawa Biver when reduced to one 



