KINETIC THEORY OF GASES 



rounded by bodies cooler than their temperature of 

 formation, they become Permanent gases. The tem- 

 peratures at which these changes occur vary from the 

 critical (or liquifying) point of Hydrogen 436 F. 

 (or 24 above the Absolute Zero, when all heat dis- 

 appears,) to that of Platinum, which melts at 3234 

 F., and vaporizes at a temperature somewhat higher. 

 The kinetic properties of a gas are as follows : A gas 

 consists of molecules of a substance that at the existing 

 temperature and atmospheric pressure retain their 

 aerial condition i. e., have no tendency to assume 

 the liquid or solid state. The molecules of which 

 they consist have a definite size and number, being 

 for every gas all exactly alike. The number of mo- 

 lecules in every gas of any constitution is exactly the 

 same at the same temperature and pressure, but they 

 vary in weight, or, as it is now called, in mass, with 

 the weight or mass of the respective molecules, and 

 thus constitute the specific gravity of the gas. These 

 molecules are in constant, active motion, moving in 

 straight lines in all directions, with uniform speed, 

 until checked by some cause. These causes may be : 

 1st. Encounters with one another, when, each being 

 elastic, they rebound and move again in straight 

 lines in their new direction until a new encounter ; 

 and so, " da capo." 2d. By impinging against the walls 

 of the containing and retaining vessel. The impact 

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