1865.] CHEMISTRY OF NATURAL WATERS. 289 



same fact in the thermal spring of Pfaffers. For further examples 

 of this kind, see Lersch, Hydro-Chemie, page 333. The carbonic 

 acid in the water of Toplitz is, according to him, not sufficient to 

 form bicarbonates unless the silica present be supposed to be com- 

 bined with a portion of bases ; while in the alkaline thermal spring 

 of Bertrich, according to the analysis of Mohr, a similar deficiency 

 of carbonic acid exists ; leading to the conclusion that a part of the 

 earthy bases present is in combination with silica and organic 

 matters. The existence of solutions holding comparatively large 

 amount of neutral carbonates of lime and magnesia, as described in 

 § 56, is not without interest in this connection ; since it at once affords 

 an explanation of the nature and origin of all such alkaline waters 

 and waters deficient in carbonic acid, as contain earthy sulphates 

 and chlorids. 



§ 68. It was found that the waters of Chambly in 1864 and 

 of the Sulphur spring of Caledonia in 1865, gave with lime-water 

 a precipitate which was soluble in an excess of these mineral 

 waters, but to a much less extent than in the acidulous saline water 

 from the High-Rock spring of Saratoga. The latter, which contains 

 bicarbonate of soda, and is highly charged with carbonic acid, turns 

 to a wine-red the blue color of litmus tincture, which is not changed 

 by the Chambly or the Caledonia water. The Saratoga water, 

 after some time, gives a feeble alkaline reaction with dahlia paper ; 

 this is more distinctly but slowly changed by the Caledonia 

 water, and almost immediately turned to green by that of Chan, My. 

 This latter water readily browns yellow turmeric paper, which is 

 scarcely affected by the water of Caledonia. 



g 69. Silica. The silica which exists in solution in cold saline 

 springs is generally very small in amount, as might be expected 

 from the insolubility of earthy silicates, which is such that super 

 ficinl drainage waters in filtering through the soil lose the silica which 

 they held in solution (§ 5). We have further shown that as a 

 result of this tendency to the formation of insoluble silicates, the 

 silicate of soda liberated in the sediments by the decomposition of 

 feldspar, generally appears at the surface as carbonate of soda, having 

 been decomposed by earthy carbonates (g 13). 



In two cases, however, considerable quantities of silica are found 

 dissolved in natural waters. The first is met with where the rapid 

 solvent and decomposing action of heated waters is exerted upon 

 alkaliferous silicious minerals (g 14), as seen in springs like 

 the Geysers. The second case is that of those rivers and streams 



Vol. II. t No. 4. 



