IX.] CHEMISTRY OF NATURAL WATERS. 151 



tion, it might be supposed that the silica in the above waters 

 exists either in a free state or as a soluble silicate with a great 

 excess of acid, The latter view, especially in the case of 

 magnesia, is rendered probable by numerous experiments 

 which form a part of the series already mentioned in 41. 

 From 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 gelatinization, always carries down with it, 

 in combination, a few hundredths of magnesia. 



In these experiments, besides the carbonate of magnesia, 

 sulphate or chloride of magnesium was present ; but the sili- 

 cated 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 sili- 

 cate 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 Kers- 

 ten 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 solu- 

 tion 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. (Amer. Jour. Science 

 (2), XII. 377.) 



Many facts in accordance with the above were observed in 

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

 water of Class III. from Belceil, Quebec, which held in 1,000 

 parts .114 of silica, besides .608 of carbonate of soda, and car- 

 bonates of lime, magnesia, and baryta, when evaporated to 

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



