SIXTH Rlil'OKT 183G. 



Objections 

 to tills ex- 

 planation. 



rimciitd of Bischof and Struve, and by the observations of 

 Turner. 



Bischof has stated*, that even long-continued boilins: in water 

 will separate the alkali from a ni;^ss of trass or volcanic tuff, 

 but that the process is facilitated by the presence of carbonic 

 acid ; so that he conceives the disintegration of felspathic rocks 

 to be brought about by water impregnated with that ingredient. 



Dr. Struve j- of Dresden, known for his imitations of some of 

 the most noted mineral springs in Germany, informs us, that 

 he has extracted alkali from granite, by merely filling a tall ves- 

 sel with small fragments of the stone, pouring upon it distilled 

 water, and suffering a stream of carbonic acid gas to rise slowly 

 through the materials, and to diffuse itself amongst the water 

 filling tlie interstices between them. 



Turner like^\'ise has pointed out the action of carbonic acid 

 and water on sucli substances in his Lecture on the Chemistry 

 of Geology, which will be afterwards adverted to. 



With respect to tlie second difficulty J, it has been argued, 

 that the majority of these springs arise from volcanic rocks in 

 which glassy felspar predominates ; that when they spring from 

 granite, they have been ascertained, in some instances to con- 

 tain potass as well as soda, as is the case at Carlsbad, and at 

 Sciionau near Toeplitz ; and in others soda alone, as at Adolphs- 

 burg and Poila in Sweden. 



It has also been remarked, that granite, in which albite has 

 taken the place of common felspar, is more decomposable than 

 usual §, so that if the water of a thermal spring were to traverse 

 a rock consisting, partly of the one kind of granite, and partly 

 of the other, it might dissolve the soda without affecting the 

 potass. 



It has been further suggested by Bischof, that in many of 

 the analyses which have been made, potass may have been mis- 

 taken for soda, and that the former is, in fact, a much more 

 common ingredient in mineral waters tlian has hitherto been 

 suspected. 



Bischof also sees a reason for deriving the alkali from the 

 contiguous strata, in the circumstance, that the thermal springs 

 of the Alps, which arise in general from primary rocks, contain 

 little or no carbonate of soda. 



To these considerations it may be replied : 



1. That the quantity of potass in tlie Carlsbad springs is too 

 inconsiderable to affect the argument ; for it was only by a mi- 



* P. 305. t Ueber Kunst. Min. Qiiellen, vol. ii. 



I See these arguments detailed in full in Bischof s Work so often alluded to. 

 § Hence sometimes distinguished as " crumbling felspar." 



