434 Action of the Atmosphere upon neiohj -deepened Soil. 



quently contained 400 times as much carbonic acid as tlie 

 general atmosphere. 



These observations will perhaps suffice to show the extensive 

 agency of this ingredient of the atmosphere upon the varied 

 matters of the soil ; its importance to the vegetable kingdom can 

 hardly be exaggerated, for it is the vital breath of plants, with- 

 out which they Avould soon perish ; its action upon the soil is 

 that of an acid, decomposing the substances with which it comes 

 in contact, and combining with the bases to form carbonates or 

 bicarbonates, which being generally soluble in Avater are thereby 

 enabled to enter into the roots of plants. Compared with some 

 of the well-marked acids — such as the sulphuric, nitric, or hydro- 

 chloric — its powers are indeed feeble ; but a rapid action upon 

 the soil is not wanted, would indeed be injurious and exhaustive, 

 for the riches of the soil would thereby be soon wasted. A 

 gradual, steady, solvent power, adapted to the continued necessi- 

 ties of plants, and most active in the summer season, is the thing 

 here required, and in this agent we find that Nature has admirably 

 supplied it.* 



Carhwetted Hydror/en is a colourless gas, about half the 

 weight of common air, scarcely soluble in water, and is a com- 

 pound of cai'bon and hydrogen. It would appear to be a neutral 

 body, not forming compounds with acids or bases. Stagnant 

 water, containing vegetable matter, frequently gives off this gas, 

 on account of which it has received the name of marslt-gas, and 

 Siiso Jire-damp, from its explosive property, so fatally known in 

 coal-mines. As I am not aware in what manner it can affect the 

 materials of the soil, it need not be longer here considered. 



Ammonia, Nitric Acid. — Although, relatively, the amount of 

 these ingredients of the atmosphere is but minute, yet, looking 

 upon the air as a whole, their quantity is considerable. Taking 

 the ammonia at even the low estimate of Fresenius (in 1,000,000 

 parts of air 0'098 by day, and 0*169 by night), it has been com- 

 puted that our atmosphei'e contains altogether 50,000,000 tons 

 ol it, and the amount of nitric acid would appear to be con- 

 siderably greater. It is only of late years that researches have 

 been made into the proportions of these substances in the air, 

 and the results of different investigators disagree, which mxight 

 have been expected, as, like the carbonic acid, their amount 

 varies probably according to time and place. Although a paper 

 by Professor Way has recently given to the readers of the 

 English Agricultural Journal a summary of the existing know- 



* ]May not one of the principal uses of the mould or carbonaceous matter of cul- 

 tivated ground be its power of dissolving the mineral matter of the soil by virtue 

 of the carbonic acid, organic acids, ammonia, and nitric acid, generated in the 

 course of its decay. 



