158 Intelligence and Miscellaneous Articles. 



stopcock ; it served to measure a constant volume of gas, which was 

 then driven into the vessel, by causing the mercury to rise. At each 

 introduction of gas the pressure increased by a quantity which was 

 measured, and which could be calculated by Mariotte's law ; the 

 results of the experiment and of calculation were compared. 



In this manner we have operated upon very various substances, — 

 Fontainbleau sand, pounded glass of different degrees of fineness, 

 and metallic filings and oxides. We have always found that the 

 pressure observed was less than that calculated ; we have therefore 

 concluded that the gases were absorbed by the solid substances. 



These absorptions present great analogy with those manifested by 

 porous bodies ; they are not produced instantaneously, but continue 

 during several hours, only attaining their limit after a period which 

 may be prolonged at pleasure ; they wiry in intensity according to 

 the nature of the gas employed, being weak with hydrogen, stronger 

 with atmospheric air, and very considerable with carbonic acid. We 

 shall give their measure by the following results, obtained with 

 pounded glass, washed and dried; the free space was 590 cubic cen- 

 timetres, in which a vacuum was produced, and the gas was then 

 allowed to fill it under the atmospheric pressure ; it absorbed — 



Carbonic acid. Air. Hydrogen. 



645 602 595 



We are convinced, moreover, that the preceding results are too 

 low, and that it is impossible to measure exactly the quantities of gas 

 contained in such spaces. When a vacuum is produced in them, 

 the equilibrium of pressure is evidently re-established very slowly ; 

 the air-pump must be worked several hours to obtain a vacuum 

 within 1 millimetre ; and besides this, pressure does not remain con- 

 stant, it gradually increases, and the action of the machine must be 

 recommenced without ever being able to attain the maximum vacuum 

 which it is capable of producing. The condensation obtained is the 

 more energetic according to the goodness of the vacuum produced ; 

 but it is necessary to remember that its exact measure is never obtained. 



Carbonic acid manifests these properties very energetically ; when 

 the powder with which the glass vessel is filled, whatever may be its 

 nature, is exposed to this gas for the first time, it absorbs it rapidly, 

 but on a second operation it has partially lost this property. The 

 vessel already mentioned received, after evacuation, successive equal 

 charges of this gas ; the increase of pressure which they produced 

 were measured, and by calculating the volume of the vessel by Ma- 

 riotte's law, there were found — 



721 cub. cent. 636 cub. cent. 629cub.cent. 627cub.cent. 622cub.c. 



After these experiments a vacuum of the same degree was again 

 produced, and the same successive introductions of gas being effected, 

 gave — 

 644cub.cent. 630cub.cent. 621 cub. cent. 620cub.cent. 616cub. c. 



From these results we must conclude, — 1, that the absorption 

 takes place with the more energy in proportion as the original pres- 

 sure is weaker ; 2, that after having once absorbed a gas, the solid 

 substance retains a considerable portion of it, of which it cannot be 



