as applied to Gases and Vapours. 541 



If the same principle here laid down for portions of atomic 

 atmosphere of any one kind of substance be considered as true 

 also of portions of atomic atmosphere of substances of diiferent 

 kinds mixed, and if it be supposed that when two or more gases 

 are mixed, there is no mutual force exerted between atoms of 

 different kinds, except the elastic pressure of the atomic atmo- 

 spheres, it will then evidently follow, — 



First, that the mixed gases will only be in equilibrio when 

 the particles of each of them are diffused throughout the whole 

 space which contains them. 



^econdlij, that the particles of each gas taken separately will be 

 in the same condition as to density, elasticity, arrangement and 

 mutual action, and also as to gravitation, or any other action of 

 an external body, as if that gas occupied the space alone. 



Thirdhj, thsit the joint elasticity of the mixed atomic atmospheres 

 at any given point will be the sum of the elasticities which they 

 would respectively have had at that point, if each gas had occu- 

 pied the space alone. 



Fourthly, that the value of the elasticity, positive or negative, 

 resulting from the attractions and repulsions of separate atoms, 

 will be the sum of the values it would have had if each gas had 

 occupied the space alone. And, 



Fifthly, that the total elasticity of the mixed gases will be the 

 sum of the elasticities which each would have had separately in 

 the same space. 



If there are any mutual actions between the particles of dif- 

 ferent gases except the elasticity of the molecular atmospheres, 

 these conclusions will no longer be rigidly true ; but they wdll 

 still be approximately true, if the forces so operating are very 

 small. This is probably the actual condition of mixed gases. 



(37.) On applying the same principle to the case of a gas 

 mixed with a vapour in contact with its liquid, it is obvious, that 

 if the attractions and repulsions of the particles of the gas upon 

 those of the vapour are null, or inappreciable, the direct effect of 

 the presence of the gas upon the elasticity assumed by the va- 

 pour at a given temperature will also be null, or inappreciable. 



The gas, however, may have a slight indirect influence, by 

 compressing the liquid, and consequently increasing its superfi- 

 cial atomic elasticity and its attractive power, on which the func- 

 tions ^ and 12 in equation (36) depend. The probable effect of 

 this will be, to make the elasticity of the vapour somewhat less 

 than if no gas were present. There appear to be some indica- 

 tions of such an effect ; but they are not sufficient to form a 

 basis for calculation. 



Supposing the gas, on the contrary, to exercise an appreciable 

 attraction on the particles of vapour, the elasticity of the latter 

 Phil, Mag. S. 4. No. 14. Suppl. Vol. 2. 2 



