REPORT ON MINERAL AND THERMAL WATERS. 25 



to be united with carbonic acid, and this is stated as being the out Car- 

 case in the maioritv of the mineral springs that contain it. ?"'"''^ ^'^"* 



Longchamp * however asserts, that in certain of the thermal 

 waters of the high Pyrenees, as at Bareges, Cauterets, St. Sau- 

 veur, and the like, the soda exists in an uncombined form, and 

 that to this must be attributed the peculiar action it exerts upon 

 the cuticle, causing the water to feel soapy and unctuous to those 

 who bathe in it. 



Anglada f questions this assertion, on the faith of experiments 

 made by him on some of these waters that had been sent him, 

 (as he says,) carefully corked ; but trials of such a description 

 cannot of course be put into competition with others instituted, 

 as those of M. Longchamp appear to have been, on the spot, 

 granting both the individuals to be competent authorities on 

 the point. 



I may also state, in confirmation of Longchamp's evidence, 

 that being at Barege some years ago, I tested the water fresh 

 drawn from the well with a solution of baryta, and found no 

 cloudiness to be produced till after it had stood some little time 

 exposed to the air, w^iilst after the addition of lime-water a 

 still longer period elapsed before any indication of carbonic 

 acid appeared. 



The experiment was tried with the same success at St. 

 Sauveur. 



Dr. Turner has also stated X, that the sjirings of Pinnarkoon 

 and Loorgootha in India, which were examined by him, contain 

 soda uncombined with an acid ; and Faraday § has confirmed 

 the statement of Dr. Black, who long ago reported the soda of 

 the Iceland springs as being in that condition. 



Now, as in many of these springs no carbonic acid is pre- 

 sent, and as the alkaline salt existing in the rock from which 

 they emerge is not a carbonate, but a silicate, we can better un- 

 derstand the possibility of the soda being found in the condition 

 stated, even if, adopting the theory of Bischof, we refer it to 

 the rock in connexion with the spring ; whilst those who lean to 

 the contrary hypothesis, and trace the alkali to the very seat of 

 the volcanic action which causes the high temperature, will be 

 able still more readily to account for its appearance in that 

 form. 



Silica appears to be an universal ingredient in thermal Silica, its 

 springs, and is perhaps present in more minute quantities even in °"S"^ '" 

 those^of all temperatures. S^nugi. 



* Annalcs de Chimie, vol. xxii. -f Memoires, p. 302. 



X Edinb. Journal of Science, No. xvii.'p. 97. 

 § Barrow's J^isit to Ireland in 1835. 



