1824.] Mineral Waters of Carlsbad. 139 



throughout and over the surface of the liquid. Every pure gas 

 which is placed in contact with water becomes instantly a 

 mixed gas in consequence of the evaporation of the liquid, and 

 the proportion of the aqueous to the permanently elastic gas 

 augments with the temperature. Unless this happened, it would 

 be impossible to expel by boiling, a greater quantity of gas from 

 water, than the difference between the augmentations of volume 

 which the elevated temperature induces upon the gas and the 

 water. But ebullition, we know, expels every particle of a gas 

 from water ; and for precisely the same reason that a gas when 

 passed through the aqueous solution of another, gradually 

 expels the latter, and finally occupies its place, so does gas 

 continue to be expelled from water in a state of ebullition, until 

 the interstices of the latter become completely occupied by the 

 newly formed vapour. But respecting the capacity of water for 

 its own peculiar gas, we, at present, know nothing: were it 

 known, it would be easy to ascertain by calculation the quan- 

 tity of carbonic acid which is contained in the Carlsbad water, 

 while confined within its subterraneous reservoir. 



The precipitate which always makes its appearance in the 

 Carlsbad water, when kept for some time, consists of silicate 

 of peroxide of iron, subphosphate of peroxide of iron, and 

 subphosphate of alumina, mixed with a substance of organic 

 origin, which is naturally colourless, but which by slow degrees 

 becomes black when exposed to the action of the atmosphere. 

 This substance appears to constitute a very common ingredient 

 in mineral waters of this nature. 1 have found it, for example, 

 in the sediment deposited by the water of the mineral spring 

 Schiers'auerling, in the neighbourhood of Kbningswart ; and 

 the silica obtained in the analysis of this water is always more 

 or less dark coloured, until the organic substance has been de- 

 stroyed by ignition. It appears to possess a peculiar affinity 

 for silica, and to associate itself with this earth in preference 

 to any of the other ingredients of the water. The silica, when 

 in combination with it, is almost black before being reduced to 

 a state of dryness ; it is then greyish coloured, but darkens 

 again when moistened. 



Examination of' some Spmdelstones. 



The sprudelstone is a radiated crystalline species of lime- 

 stone, which exhibits no traces of a foliated texture. Its colour 

 is sometimes white and sometimes brown, and not unfrequently 

 alternates in white and brown stripes. The texture varies 

 extremely in different specimens ; sometimes it is most deci- 

 dedly radiated, at other times it is almost compact ; and speci- 

 mens of the latter description are not unfrequently transparent 

 when in thin fragments. Some of the white varieties possess 



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