276 SOILS. 



the amount of absorption admonishes us that in all these cases, 

 to secure disinfection the earth to be used should contain as 

 much clay as possible, and should not be mere sand, as is 

 sometimes the case. It also shows that the addition of charcoal 

 to such materials does not increase their efficacy, as has been 

 supposed, but that an equal bulk of clay would be more effi- 

 cient. 



Of course, so soon as the absorbing cylinders used for this 

 experiment are exposed to the atmosphere, the principle above 

 stated in regard to " partial pressure " asserts itself. The ab- 

 sorbed gases quickly begin to be given off, and in some hours 

 the equilibrium with the ordinary conditions of the atmos- 

 phere is reestablished. That the strong absorptive power of 

 soils for ammonia is to some extent effective in maintaining 

 the supply of this substance by absorption from the atmos- 

 phere, cannot be doubted. 



Boussingault, and later Stenhouse, determined the absorp- 

 tive power of wood charcoal for ammonia to be 90 and 98 

 volumes respectively. 



THE COMPOSITION OF GASES ABSORBED FROM THE ATMOS- 

 PHERE BY VARIOUS SOLIDS. 



In 1864 and 1865 Reichardt and Blumtritt l investigated 

 elaborately the composition of gases driven off by heat from 

 various powders, including soils, exposed to the atmosphere. 

 All the substances examined were therefore " air-dry," there- 

 fore to a certain extent moist ; and the presence of this aqueous 

 vapor of course modifies in a measure the results that would 

 have been obtained had the materials used been exposed to dry 

 air only. They found that, as had already been stated by 

 previous observers, the presence of capillary water diminishes 

 materially the absorption of gases, especially of those not as 

 easily absorbed by water as are carbonic gas and ammonia. 

 Contrary to what might have been expected from the more 

 ready condensation of oxygen by pressure or cold, in nearly all 

 cases nitrogen is absorbed to a greater extent than oxygen, 

 and sometimes exclusively so; so that in some cases the latter 

 was found to be present only in traces, as will be perceived 

 from the subjoined table: 



1 Journal fur praktische Chemie, Vol. 98, p. 167. 



