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 absorbed gases quickly begin to be given off, and in some hours the equilibrium with the ordinary conditions of the atmosphere is re-established. 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 atmosphere, cannot be doubted. Boussingault, and later Stenhouse, determined the absorptive power of wood charcoal for ammonia to be 90 and 98 volumes respectively. THE COMPOSITION OF GASES ABSORBED FROM THE ATMOSPHERE BY VARIOUS SOLIDS. In 1864 and 1865 Reichardt and Blumtritt[99] 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,” therefore 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: