108 VAPORS, OASES. 



58. Mixture of Unequal Volumes of Gases hav- 

 ing Unequal Pressures. Two volumes r, v', of dif- 

 ferent gases, at the respective pressures p, p', are mixed 

 together so that the volume of the mixture is V ; to 

 find the pressure of the mixture. 



Change the volume of each gas to F; their pressures will 

 be, respectively (Art. 48), 



v v' , 



yP> -yP> 



and therefore (Art. 57) the pressure of the mixture is 



and if P be this pressure, we have 



P V = pv + p'v'. 

 (See Besant's Hydromechanics, p. 114.) 



59. Vapors, Gases. The term vapor is applied to 

 those gaseous bodies, such as steam, which can be liquefied 

 at ordinary pressures and temperatures ; while, the word gas 

 generally denotes a body which, under ordinary conditions, 

 is never found in any state but the gaseous. The laws 

 already stated of gases are equally true of vapors within 

 certain ranges of temperature, the only difference between 

 the mechanical qualities of vapors and gases, as distinguished 

 from their chemical qualities, being that the former are 

 easily condensed into liquids by lowering the temperature, 

 while the latter can be condensed only by the application 

 either of great pressure or extreme cold, or a combination of 

 both. 



Prof. Faraday succeeded in condensing a number of different gases ; 

 he found that carbonic acid, at the temperature of 11, was liquefied 

 by a pressure of 20 atmospheres, but when it was at the temperature 



