432 Action oftlie Atmosphere upon neiohj -deepened Soil. 



lOCO grammes of the carbonic acid solution, after 4 hours' 

 digestion, contained — 



Grammes. 



Silica 0-09544 



Bicarbonate of lime .. .. 0-16893 

 ,, magnesia .. 0-05333 



„ soda .. .. 0-06299 



„ potash .. .. 0-00189 



0-38258 



The powerful action of water containing carbonic acid, upon 

 carbonate of lime, is well known, removing the lime in the form 

 of bicarbonate ; should the water holding the lime in this state of 

 solution be exposed to evaporation, the lime is deposited, and in 

 this way great masses of limestone are formed — witness the t7'a- 

 vertino of Italy and the large accumulations in the plains of 

 Pamphylia. The same is also seen in the stalactltic caves in 

 this and other countries. 



The late Sir H. De la Beche, speaking of the decomposition 

 of silicates, and remarking that certain of them — for example, those 

 of potash and soda — are not difficult to be dissolved when free 

 carbonic acid Is present, goes on to say : " Mr. Henry informs me 

 that, when experimenting upon silica, he found that a silicate of 

 soda was decomposed even by the carbonic acid of the atmo- 

 sphere, and the silica deposited, its state and appearance being 

 much affected by the degree of concentration of the solution." 

 {Geological Observer, p. 606.) 



As with silicates of potash and soda, so It is with the silicate 

 of lime in the presence of water containing carbonic acid, decom- 

 position taking place with the formation of carbonate of lime, or, 

 if the carbonic acid be in abundance, bicarbonate of lime ready 

 to be removed in solution. [De la Beche.) 



Way has moreover shown the solvent action of carbonic acid 

 upon the double silicate of alumina and ammonia. Thus, while 

 one gallon of distilled water dissolved from this salt but one grain 

 of ammonia, the same quantity of water saturated with carbonic acid 

 dissolved upwards of 2i grains. {Eng. Agricult. Journ., XXIX. 

 p. 136.) 



Again carbonic acid is, says Liebig, the indispensable condition 

 for the entrance of the phosphates into the vegetable organism ; 

 for phosphate of lime, although insoluble in pure water, yet is, like 

 carbonate of lime, soluble in water containing free carbonic acid ; 

 and, according to Werner, it is the carbonic acid that decomposes 

 the felspar of rocks, an opinion which appears to be pretty gene- 

 rally enlertalned. 



Dr. Anderson, of Glasgow, says, " The oxygen of the atmo- 

 sphere acts upon the organic matters of the soil and produces a 



