430 Action of the Atmosphere upon newly-deepened Soil. 



of carbonic acid, and the combination of this with high pressure, 

 as in the case of soda-water, will cause a very highly charged 

 solution of the gas. Carbonic acid is a transparent gaseous sub- 

 stance, considerably heavier than common air, and, as its name 

 implies, is possessed of acid properties, entering into combination 

 with bases to form salts, which are termed carbonates ; as it is, 

 however, but a feeble acid, its salts are generally decomposed in 

 the presence of other free acids, with effervescence : the acid also 

 may be driven off by heat, which, however, sometimes requires to 

 be very intense. The carbonates are more or less soluble in 

 water, many of them, however, but very sparingly so ; but when 

 the water contains an excess of carbonic acid, its solvent power 

 is thereby much increased. Carbonic acid is capable of being 

 liquefied under great pressure, and may ^ven be reduced to the 

 solid form. It dilates remarkably by heat, its expansion being 

 more than four times that of air. It is formed abundantly by 

 the decay of dead organic matter, the carbonaceous substances 

 of the soil uniting with oxygen and thereby giving rise to it 

 in considerable quantity. It is found also, to a gi-eater or less 

 extent, in all springs, and indeed in all natural waters. Through 

 its solvent powers it is that the mineral matters of the soil are 

 brought into forms fit for being taken up by the rootlets of 

 plants. Speaking of the mineral ingredients of the soil, Daubeny 

 says, " All that which water impregnated with carbonic acid 

 fails in dissolving ought to be regarded as at present contri- 

 buting nothing to the food of a plant, although it may ultimately 

 become available for its purposes." {^Eng. Agricult. Journ. 

 VII. 237.) 



Dr. Struve, of Dresden, stated that he extracted alkali from 

 granite by merely filling a tall vessel with fragments of the stone, 

 pouiing upon it distilled water, and suffering a stream of carbonic 

 acid gas to bubble slowly through the materials. 



Some interesting experiments were made by Professors W. B.. 

 Roo-ers and R. E. Rogers, of Virginia. Referring to the prolonged 

 dio-estion of minerals in water, and carbonic acid water, at the 

 ordinary temperature of 60°, they gave results obtained with horn- 

 blende, epidote, chlorite, mesotype, &c. (minerals which often 

 largely enter into the composition of the soil), showing that the 

 amount of solid matter dissolved by the carbonated water in many 

 cases is quite sufficient for a qualitative analysis, even when the 

 digestion has only been continued for 48 hours ; when further 

 prolonged they have procured from the liquid a quantity of lime, 

 mao-nesia, oxide of iron, alumina, silica, and alkali, the dissolved 

 ino'redients of these mineials amounting sometimes to nearly 1-per 

 cent, of the whole mass. Their experiments further demonstrate 

 that in water impregnated with carbonic acid, carbonate of mag- 



