Krug von Nidda on the Mineral Springs of Iceland. 107 



thering of the mountain-rocks, that consist chiefly of combinations 

 of silica with soda, potash, and alumina ; it is distinctly marked 

 in the formation of porcelain earth from felspar. This combina- 

 tion of silica with alkalies, in which the silica performs the part 

 of an electro-negative body, is decomposed by an acid in which, 

 though one of the weakest of the real acids, the electro-negative 

 character is exhibited in a much higher degree than in the silica, 

 viz. by the carbonic acid. This latter, though an accidental con- 

 stituent of the atmosphere, is yet universally distributed, is com- 

 bined with the atmospheric water, penetrates through cracks and 

 fissures into masses of rock, and is thus enabled gradually to 

 decompose those silicates of soda and potash. When the alkali 

 quits its previous combination, it dissolves a portion of the silica, 

 and carries it forth in the spring water. But what is accom- 

 plished by the long-continued action of weak carbonic acid, is 

 effected in a higher degree by the stronger acids, as sulphuric 

 and muriatic acids, when these occur in mineral waters and come 

 in contact with rocks containing soda or potash. 



It would seem, therefore, that it is only requisite for water, 

 impregnated with carbonic acid, to unite with the soda and po- 

 tash of those rocks which it penetrates by means of clefts and 

 fissures, in order to make its appearance as a mineral spring. 

 We can thus so far follow up the idea that all mineral springs 

 are the result of a mere simple dissolving process : but whence 

 are derived the carbonic, sulphuric, and muriatic acids, which 

 are partly combined with Abases, and partly contained in a free 

 state in mineral waters. Can they also be regarded as the 

 products of a simple process of solution ? We may perhaps 

 consider deposits of rock-salt as the sources from which the 

 muriate of soda has been derived, though geological facts are in 

 most cases adverse to such a supposition ; but we know of no 

 combination either of carbonic or sulphuric acid, from which, 

 without the intervention of other substances, the acid can be 

 separated in order to unite with the water with which it comes 

 in contact. Carbonic acid is so universal a constituent in springs, 

 that there is probably not a single one which does not contain 

 more or less of it. If we suppose that it is in part derived from 

 the atmosphere, and that it unites with the atmospheric water, 

 or that it has resulted from the decomposition of organic sub- 



