68 Dr Davy oti Carbonic Acid 



more readily than carbonate of lime does or carbonate of 

 magnesia. May not this greater facility be concerned in 

 many instances, especially of the grains of the cerealia, in 

 occasioning the preponderance of the one compound greatly 

 over the other, — the one so much more important than the 

 other in these grains as articles of food ■? Farther, as silica 

 appears, after having been dissolved by means of carbonic 

 acid, not to be deposited distinctly on the escape of the acid, 

 but rather on the evaporation of the aqueous part, may not 

 this circumstance aid to explain the deposition of silica which 

 is observable on the ripening of the cerealia and grasses at 

 a period when they are losing their humidity, and becoming 

 dry, and strong, and resisting 1 



Some of the results I have described bear, I believe, on 

 other points of inquii\v, — for instance, on soils, and even the 

 strata on which they rest, and mineral waters. The effects 

 of the solvent power of rain containing carbonic acid on cer- 

 tain ingredients of the soils, after what has been adduced, is 

 obvious. When new deposits are formed, connected with 

 the escape of carbonic acid gas, whether entirely, as in the 

 production of stalactitical limestone, or in part, as in the 

 foi'mation of freestone with a calcareous cement, should we 

 not expect to meet, mixed with the deposited carbonate of 

 lime, some carbonate of magnesia and phosphate of lime 1 

 In the few instances in which I have sought for these latter 

 compounds, in situations in which it seemed reasonable to 

 expect them in admixture with cax'bonate of lime, I have not 

 failed to find them ; for example, in stalactites now forming, 

 pendent from cavernous roofs, in the rock of which are traces 

 of phosphate of lime and of carbonate of magnesia. 



If, as the results of the experiments described seem to 

 shew, silica is capable of being dissolved by water impreg- 

 nated with carbonic acid gas, should it not follow that silica 

 ought to be met with in mineral waters whenever abounding 

 in this gas, provided the source or the strata through which 

 they pass contain silica in a favourable state of minute divi- 

 sion to be acted on 'i And, as far as my experience extends, 

 this is the case. Many instances might be adduced, in which 

 the proportion of silica in mineral waters seems to bear very 



