1823.] Mathematical Principles of Chemical Philosophy. 255 



Pkop.VII. 



Gases are attracted by solids or liquids, whether they do or 

 do not exert on them any chemical action. - 



From the nature of attraction, the particles of a gas when 

 indefinitely near the surface of solid or liquid matter, will tend 

 to it ■ therefore upon the surface of every substance which is 

 surrounded by any gas or vapour, there will be an atmosphere 

 of that gas or vapour, of very small extent, whose density is 

 oreater than that of the surrounding medium, whose increased 

 elastic force is balanced by that of the surrounding medium, and 

 its tendency to the body. Q. E. D. 



Cor. 1. —Hence bodies which are filled with minute pores will 

 absorb large quantities of gaseous matter. . _ 



Cor. 2.— Hence liquids will contain air for which they may 

 have no chemical attraction. 



Cor 3 —The rays of light will be refracted and dispersed by 

 passing near the surface of any solid ; this will be distinct from 



n Cor 4 —When a dry porous body, freed from air, is brought 

 into any gas or vapour, its temperature will be increased. 



Cor 5 —AH bodies may be more or less perfectly freed Irom 

 air by being heated, or placed under an exhausted receiver. 



Scholium. 

 Prop. 6 and 7 explain some curious phenomena. Charcoal 

 and other very dry porous substances absorb a large quantity of 

 any oa S or vapour in which they are immersed, the volume of 

 g ;as absorbed being many times greater than that of the solid ; 

 hence very dry impalpable powders cannot be readily mixed 

 with liquids. Hence also during the absorption of a gas by a 

 porous solid, heat will be evolved, and upon this principle, the 

 common pyrophorus seems to act. 



General Remarks upon Chemical Attraction. 



Chemical attraction is distinguished from that which produces 

 mere mechanical effects, by many remarkable differences in the 

 properties of the resulting compounds. _ 



Introduce an inflamed stream of hydrogen into a vessel ot 

 oxygen gas; both gases will rapidly be condensed, and the 

 only product will be water. In this experiment, the gases enter 

 into chemical union, i. e. into that state of combination in which 

 the attraction subsisting between the particles of the oxygen and 

 hydrogen gases, overcomes their elastic force, and is greater 

 than the force exerted by like particles upon each other ; hence 

 the water may be congealed, reduced to a state of vapour, or 

 enter into many combinations, without any decomposition tak- 

 ing place. The sensible qualities of the gases are totally 



