CARBONATION AND VEGETATION. 475 



Fleck, as cited by Letts and Blake, found in the .soil at a depth of 6 

 meters by volume a minimum amount of carbon dioxide of 4.22 per cent, 

 and a maximum amount of 7.96 per cent; at 4 meters, a minimum amount 

 of 4.11 per cent and a maximum amount of 5.56 per cent; at 2 meters, a 

 minimum amount of 2.99 per cent and a maximum amount of 2.91 per cent 

 (the last number must be a misprint)." 



These figures show that the amount of carbon dioxide in the ordinary 

 air is insignificant in comparison with the amount in soils in regions of 

 luxuriant vegetation. In such regions the carbon dioxide is from thirty to 

 more than one hundred times more abundant than in the atmosphere. 

 This large "amount is mainly furnished by the decomposition of vegetation, 

 although, as shown by Briggs, even dry soils have the power to absorb 

 carbon dioxide from the atmosphere.'' 



The process of carbonation is dominantly accomplished by the. substi- 

 tution of carbonic for silicic acid. The negative side of this process is 

 desilication. To a very ,small extent carbonation is accomplished by the 

 substitution of carbonic acid for other acids — for instance, phosphoric acid. 

 Also carbonates are produced on a considerable scale by the union of 

 carbon dioxide with the oxides which were not united with other acids, as, 

 for instance, ferrous oxide in magnetite. 



Mueller has experimentally ascertained that carbon dioxide in water at 

 ordinary temperatures and pressures is capable of attacking many minerals. 

 Of the oxides, he experimented with magnetite; of the silicates, he experi- 

 mented with orthoclase, oligoclase, hornblende, olivine, serpentine, and 

 muscovite. He also experimented upon a number of phosphates, including 

 apatite. While all of the silicates experimented with were attacked to 

 some extent, there was great variation in the rate of action. For instance, 

 orthoclase is attacked more readily than olig-oclase ; hornblende and serpen- 

 tine are attacked more rapidly than the feldspars, and olivine is the most 

 readily attacked of all the silicates tested. The process of carbonation 

 formed carbonates of sodium, potassium, calcium, magnesium, and iron. 

 Alumina also went into solution. The liberated silica partly went into 

 solution, but partly also separated as quartz. Magnetite was the most 



"Letts, E. A., and Blake, E. F., The carbonic anhydride of the atmosphere: Sci. Proc. Royal 

 Dublin Soc, vol. 9, pt. 2, 1900, p. 215. 



6 Cameron, Frank K., Soil solutions, their nature and functions, and the classification of alkali 

 lands: Bull. TJ. S. Dept. Agric. No. 17, 1901, p. 17. 



