A CENTURY OF CHEMISTRY. 93 



from the kinetic theory of gases, taken in connection 

 with Avogadro's law. 



Kinetic Theory of Gases. — As facts began to ac- 

 cmnulate showing a remarkable uniformity in the 

 behaviour of different gases to the same changes of 

 temperature and pressure, the need for some concep- 

 tion of the nature of a gas made itself felt in many 

 minds. The early suggestions of Daniel Bernouilli 

 (1738) and of Waterston, Graham's discovery of the 

 law of diffusion, the work of Herepath, Joule and 

 Kronig, the achievements of Clausius (1857-1862) 

 and Clerk Maxwell (1860-1867), are some of the 

 steps in a long history — the history of the kinetic 

 theory of gases, one of the revolutionising concepts of 

 modern science. According to this theory, a gas 

 consists of innumerable particles moving with high 

 velocity, overflowing into any free space which is 

 available, thus securing that there is the same aver- 

 age number in every unit of volume, impinging on 

 the contained walls, if there are any, and thus caus- 

 ing pressure which must obviously increase with the 

 number of the molecules and the mass and velocity 

 of each. Such is at least a suggestion of the view 

 which gave new life to the atomic theory, and that at 

 a time when it was languishing for support. When 

 it was shown that precise and workable conceptions 

 could be formed of the rectilinear movements of 

 molecules in a gas, when the internal motion of the 

 atoms composing the molecules was shown to be a 

 needful assumption, when the rate of velocity of a 

 particle of hydrogen gas was actually calculated, 

 when the laws of Boyle, Gay-Lussac, and Avogadro 

 were brought into harmony, and so on, — chemistry 

 became, in a more real sense than before, a study of 

 the changes of equilibrium in atoms. 



