Mr. Ivory oti the Constitution of the Atmosphere. 279 



The volume of the mixture being V, if D be its density, we 

 shall evidently have 



vp + u'p' + v"/ = VD: 

 and hence 



VD = (Ay + A' y' + A" u") R. 

 Now we may assume 



V = Au+ MxJ + A'V; 



and in consequence D = R : so that the mixture can be no 

 other than atmospheric air, since both have the same pressure, 

 density, and temperature. If to the equation just found we 

 join the former one, viz. 



V = V + v' + v", 

 both are not sufficient for determining the three volumes when 

 a given value is assigned to V : and therefore it seems neces- 

 sary to ascertain one of the volumes by experiment in order 

 to arrive at the knowledge of the other two. It is generally 

 admitted that the carbonic acid gas never exceeds xo'^oth of 

 the volume of air. It has even been established that the car- 

 bonic acid gas in a volume of air varies between jouo o^'^ ^^^ 



V 

 TOGO til *• Wherefore, taking y" = — — , and V =s 100, the 



two equations will become 



99-84-8 = A u + A' i/, 



99-9 = u + u' ; 

 whence we obtain 



Oxygen v = 20*5 



Azote i/ = 79-3 



Carbonic acid u" = 0* 1 



99-9 



It thus appears that the carbonic acid gas taken at the 

 greatest valuation, very slightly alters the proportion of the 

 oxygen and azote. 



Besides the three gases already mentioned, the atmosphere 

 generally contains a portion of aqueous vapour; and we have 

 next to inquire in what manner this vapour will mix with dry 

 air in an atmosphere at rest and in equilibrium. Let V de- 

 note a volume of moist air consisting of aqueous vapour of 

 the tension ot, measured in inches of mercury, and of dry air, 

 the barometric pressure of which is p, and its volume u: and, 

 first we may suppose that v is less than V, in which case the 

 elasticity p of the dry air diffused through the volume of 



* Coviptes Rendus, June 7, 1841, p. 1023. 



