102 CHEMISTRY OF NATURAL WATERS. [IX. 



mentioned in 5. Hence it happens that apart from the 

 neutral soda-salts of extraneous origin, waters permeating sedi- 

 ments containing alkaliferous silicates generally bring to the 

 surface little more than soda combined with carbonic and 

 sometimes with boric acid, and carbonates of lime and magne- 

 sia with small portions of silica. 



14. This explanation of the decomposition of alkaliferous 

 silicates and of the origin of carbonate of soda is opposed to 

 the view of Bischof, who conceives that carbonic acid is the 

 chief agent in decomposing feldspathic minerals.* The sol- 

 vent action of waters charged with carbonic acid is undoubted, 

 as shown by various experimenters, especially by the Messrs. 

 Kogers,t but this acid is not always present in the quantities 

 required. The proportion of it in atmospheric waters is so 

 inadequate that it becomes necessary to suppose some subter- 

 ranean source of the gas, which is by no means a constant 

 accompaniment of natron-springs. A copious evolution of 

 carbonic acid is observed in the vicinity of the lake of Laach, 

 where the alkaline waters studied by Bischof occur. J The 

 same thing is met with in many other localities of such springs, 

 among which may be mentioned the region around Saratoga, 

 where saline waters containing carbonate of soda, and highly 

 charged with carbonic acid, rise in abundance from the lower 

 palaeozoic strata ; but farther northward, along the valleys of 

 Lake Champlain and the St. Lawrence, similar alkaline-saline 

 waters, which abound in the continuation of the same geologi- 

 cal formations, are not at all acidulous. From this the conclu- 

 sion seems justifiable that the production of carbonate of soda 

 is a process, in some cases at least, independent of the presence 

 of free carbonic acid. In this connection, it is well to recall 

 the solvent action of pure water on alkaliferous silicates, as 

 shown more especially by Bunsen, and also by Damour, who 

 found that distilled water at temperatures much below 212 

 takes up from silicates like palagonite and calcined mesotype 



* Bischof, Chem. Geol., II. 131. 

 t Amer. Jour. Sci. (2), V. 401. 

 t Bischof, Lehrbuch, I. 357-363. 



