Action of the Atmosphere upon neiohj-deepened Soil. 449 



The following, from Saussure, shows the absorptive power of 

 boxwood charcoal on some gases : — 



1 vohime of charcoal absorbs of — 



Volumes. 



Ammoniacal gas 90 



Sulphuretted hydrogen 55 



Carbonic acid 35 



defiant gas 3a 



Carbonic oxide !)'42 



Oxygen 9-25 



Nitrogen 7*5 



Hydrogen 1'75 



The following table, from Schubler, Avill give some idea of the 

 relative absorptive properties of different kinds of earth : — 



^loisture absorbed Oxygen absorbed 



by 1000 grains of dry by looo grains of moist 



Earth on a surface Earth in 3U days 



of 50 square inches in from 15 cubic inches 



72 hours. of Air. 



Grains. Per Cent. 



SiUceous sand 1"6 



Gypsum powder 1 2*7 



Calcareous .sand 3 5-(! 



Arable soil 23 lfi-2 



Sandy clav 28 9-3 



Slaty marl 33 H'O 



Loamy clay 35 11"0 



Fine lime "^ .'55 10-S 



Stiff clay 41 13-6 



Grey pure clay 49 15*3 



Garden moald 52 IfS'O 



Fine magnesia 82 17-0 



Humus ■ 120 20-3 



None of these earths absorbed any oxygen when in a perfectly 

 dry state. It will be remarked how nearly the same the order is 

 in which they absorb these two substances. 



With regard to the property of the earth to suck in moisture, 

 oxj'gen, ammonia, and otlier gases, the humus or organic matter 

 of the soil is found to have a more powerful effect tlian any other 

 ingredient, although clay, oxide of iron, and magnesia, are also 

 great absorbers ; for it is found that if a portion of" earth is burnt 

 and its humus thus volatilized, while the oxide of iron is raised 

 to a higher degree of" oxidation, its power of absorbing oxygen 

 becomes considerably dimniishcil, and, according to Schubler, in 

 sonur instances disapjicars ; and \\ av found in his experiments 

 that the power of a soil to combine with ammonia, fdtered through 

 it in solution, was greatly diminished by burning it, and that the 

 more strongly the soils were burnt the more comj>letclv was their 

 absorptive power destroyed, whether they had previously contained 



