ABSORPTION BY SOILS. 



275 



the latter containing 1.2% of humus. As to the peat, since its 

 weight was only .5 grams against an average of 2 grams for 

 the soils employed, its absorptive power by weight doubtless 

 exceeds all other substances. 



ferruym. BMck 

 soil fldobe 



adobe clay 



^ 



Ammonia oas 



FIG. 51. Absorption of Carbonic and Ammonia Gases by different Soils. 



While the experiment shown in the figure serves as a con- 

 venient and striking demonstration for lecture purposes, it is 

 of course not adapted to a direct comparison of the absorbing 

 powers of the several substances, because of different heights 

 of the mercurial columns counteracting the atmospheric pres- 

 sure. For direct comparative measurement the tubes must be 

 sunk in mercury so as to equalize the levels inside and outside, 

 since the corrected volumes obtained by calculation would not 

 serve the purpose. 



According to special measurements made under normal 

 atmospheric pressure, the writer found that a black clay soil 

 ("adobe") absorbed (at 6oF) over two hundred times its 

 bulk of ammonia gas, while under the pressure of one-fifth of 

 an atmosphere (as shown in the photograph) the absorption 

 was one hundred and twenty-three times its bulk. This ener- 

 getic absorption of ammonia and related gases explains the 

 marked disinfecting effects which a covering of dry earth 

 exerts in the case of cemeteries, manure piles, and earth closets. 

 But the difference between the sandy soil and the clay soil in 



