ABSORPTION BY SOILS. 2 8l 



land the amount of oxygen transformed into carbonic gas will 

 be greatest, while in the surface-soil of ordinary fields, car- 

 bonic gas rarely reaches to as much as one per cent. In all 

 cases, however, the content of carbonic gas in the air of the 

 soil is materially higher than that of the air above it, and thus 

 serves to intensify greatly the solvent and disintegrating effect 

 of the soil water upon the soil materials (see chap. 2, p. 17). 

 The soil-mass itself, however, retains carbonic dioxid with con- 

 siderable tenacity, so that it is not possible to wash it out com- 

 pletely by filtering water through it. When water containing 

 carbonic gas in solution is filtered through the soil, the gas is 

 sometimes completely absorbed, the water passing off free 

 from gas. 



The presence of free carbonic gas in soils is readily demon- 

 strated by passing through the warmed soil a current of air, 

 which is then made to bubble through lime water; a clouding 

 of the latter, and the ultimate formation of a precipitate of 

 calcic carbonate, proves the presence of the gas, and may also 

 serve to measure its amount. 



From the fact that the free air in normal soils may contain 

 as much as one-fortieth of its bulk of carbonic gas, besides 

 what may be contained in the condensed form, we may con- 

 clude that this gas is formed within them with considerable 

 rapidity ; for otherwise, in view of the free communication and 

 diffusion with the outer air, such large amounts could not be 

 maintained in the surface-soil. Doubtless a considerable pro- 

 portion of the carbonic gas normally contained in the atmos- 

 phere is thus supplied from within the soil itself. 



Relation of Carbonic Gas to Bacterial and Fungous Activity. 

 It has been fully demonstrated by the researches of Koch, 

 Miquel, Adametz, Fuelles, Wollny and others, that the forma- 

 tion of carbonic gas in the soil is not a purely chemical oxida- 

 tion process, but is essentially dependent upon the presence and 

 life-activity of numerous kinds of organisms, bacterial as well 

 as fungous. The crucial proof of this fact is that the presence 

 of any antiseptic diminishes, and if exceeding certain propor- 

 tions completely suppresses, the formation of carbonic gas; 

 while on the other hand all conditions known to be favorable 

 to the life of such organisms, viz., the proper conditions of tem- 

 perature and moisture (varying with different kinds), increase 



