1815.] ihe Gases ly different Bodies. 253 
All the bodies with which these experiments were made, ex- 
cepting charcoal and hydrophane, from the way in which I treated 
them before the absorption of the gases, imbibed’ a good deal of 
mercury. No attention was paid to this, as it appears that the 
volumes absorbed of the little absorbable gases are smaller than the 
‘size of the pores of the absorbing bodies. 
6. Influence of the Affinity and Elasticity of the Gases, and of the 
Porosity ofthe solid Bodies on the Absorption. 
The rate of absorption of different gases appears to be the same 
in all bodies of similar chemical properties. All the varieties of 
asbestus condense more carbonic acid gas than oxygen gas ; woods 
condense more hydrogen than azote. But the condensations them- 
selves in different kinds of asbestus, or wood, or charcoal, are very 
far from being equal. Ligniform asbestus absorbs a greater volume 
of carbonic acid gas than rock cork ; so does hydrophane than the 
swimming quartz of St. Quen and the quartz of Vauvert ; and the 
absorption of gases by box-wood charcoal is much greater than by 
fir charcoal. These differences are not in the least altered if, 
instead of equal volumes, equal weights of charcoal be em- 
ployed. 
Count Morozzo thinks he has observed that the most combustible 
charcoal, and that which is most proper for the preparation of gun- 
powder, possesses the smallest power of absorbing gases; and con- 
ceives that this may be owing to a chemical difference in the com- 
position of charcoals. ut as the analysis of charcoals of very 
different absorbing powers shows always the same constituents, this 
explanation must be renounced; and we must rather ascribe the 
cause of this difference to the physical state of the charcoal, as, 
for example, to the number and size of the pores which it con- 
tains. 
To be able to determine the influence which the porosity or the 
state of aggregation of solid bodies has upon their power of absorb~ 
ing gases, 1 compared with each other the quantities which the 
same piece of box-wood charcoal absorbed when whole, and when 
reduced to an impalpable powder. ‘The piece of charcoal weighed 
2°94 grammes (454 grains troy), and had a volume of 4°92 cubic 
centimetres (0°3 cubic inch English), and absorbed, when freed 
from air by the air-pump, 351 cubic centimetres (2°731 cubic 
inches), or about 71 times its volume of atmospherical air. It was 
now rubbed to an impalpable powder, and put into a glass tube, 
both the ends of which were shut up with gauze. In this state its 
weight was the same as before; but its volume was 7°3 cubic centi- 
metres (0°445 cubic inch) ; and when freed from air by the air- 
pump, it absorbed only 20°8 cubic centimetres (1°355 cubic inch) 
of atmospherical air. ‘I'hus it absorbed about three times its volume 
in a pulverized state, and about 74. times its volume when whole: 
80 that by destroying, opening, and widening, the small cells of the 
