308 Mitchell on the Penetrativeness of Fluids. 



Secondly. We are struck with an unexpected result, the great 

 POWER of gases to infiltrate each other. It has been long known, 

 that aeriform substances confined in the same apartment, finally 

 mingle uniformly, and that, even if the lighter one be placed above 

 the other. To account for this, and some other facts of the same 

 class, Mr. Dalton supposed that each gas, in reference to the verti- 

 cal relation of its particles, stood in an attitude of independence of 

 any other gas present, as much as if no such gas were confined along 

 with it, no particle of one gas being supposed to rest on any parti- 

 cle of the other, the interstitial cavities of one gas being in fact a 

 vacuum for the reception of the molecules of the other, each for 

 each. 



The power, however, of this infiltration being known, we are 

 entitled to conclude, that the interspaces of gases are reciprocally 

 occupied with a force similar, and probably equal to that which 

 causes the imbibition of liquids by solids, and produces solutions of 

 substances, even of the highest cohesive attraction. Solutions may 

 now be esteemed infiltrations by solids and liquids of the tissues of 

 each other, requiring, perhaps, only a fitness in size, rather than a 

 chemical or cohesive attraction, for we see it subverting even the 

 greatest cohesive power, and holding no apparent relation with 

 known chemical affinities. 



The atmosphere cannot any longer be considered as admixture in 

 the common acceptation of the term. Its gases penetrate each 

 other interstitially with great mechanical force, so great as to defy 

 all mere mechanical means of separation. It is an exemplification of 

 solution. 



When the particles of a solid separate and enter the tissue of a 

 liquid, it is termed solution, when the liquid penetrates the solid, 

 and the latter maintains its solidness, it is usually called infiltration, 

 imbibition, absorption, &c. &c. The processes are perfectly alike in 

 principle, the different names being expressive of that, and of certain 

 accompaniments or effects also. 



By means of our second generality, we are enabled satisfactorily 

 to explain many phenomena not heretofore easily accounted for. 

 Thus we understand how a gas or odour flows so rapidly through 

 the whole tissue of a still atmosphere, and why some gases do so 

 more speedily than others. An explanation is also given of the 

 diffusion of odours, even against a draught, or current, and it 

 accounts for this fact, among others, that brimstone thrown into the 

 fire, is perceived by the olfactories, when the draught of the chimney 

 is even perfect. 



