82 Mr. Ivory on Mixed Gases. 



the same envelop as the first, it will expand by its elasticity, 

 and will force its way by continued agitations through the 

 obstruction of the quiescent gas, in like manner as this ex- 

 panded through a vacuum ; the only difference being that the 

 agitations will continue longer in one case than in the other. 

 After a time, as there is no mutual action of the particles of 

 the two fluids, all the agitations will cease ; the first gas will 

 resume its state of rest; and the new gas will be diffused with 

 a uniform density and pressure through tlie envelop. 



We have next to inquire. What is the elastic force of the 

 combined gases, or which is the same thing, what is the ex- 

 ternal pressure that must be applied at the common surface, 

 in order to confine them both without change of volume. 

 When the first gas alone was contained in the envelop, we 

 have found that the elastic force of the expanded gas v.as 



p '-^'- but when both gases are present in the envelop, the pres- 

 sure p . -^ upon the space of the envelop equal to the unit of 



surface, which space is equally in contact with both fluids, will 

 cause a compression of the second gas as well as of the first. As 

 the two fluids are separately in equilibrium and have no mu- 

 tual action upon another, it is easy to discover that the same 

 compressive force applied on the same space of the common 



surface will transmit pressures equal to p . ^ to the particles 



of both fluids. But the elastic force of the particles of the 



o' 

 second gas beings' when the volume is u', it will be p' '-yi 



when the volume is V; to which adding p . -^ , the in- 

 crease of elasticity caused by the action of the first gas on the 



VI), 



envelop, the sum p' . tt- + i? • -t? vvill be the whole elastic 



force of the particles of ihe second gas. As the two fluids 

 are similar and interchangeable in their conditions, the like 

 reasoning will show that the whole elastic force of the particles 

 of the first gas, caused by the action of both gases on the en- 

 velop, is p ' -Tf + P'- ^ • Wherefore, if P represent the 



elastic force of the mixture, we shall have 

 r. , v' 



P==P-Y+P''Y- 

 The foregoing view is in accordance with that part of the 



