92 MOLECULAR MOTION AND ITS ENERGY 40 



CHAPTEE IV 

 IDEAL AND ACTUAL GASES 



4O. Inexactness of the Theoretical Laws 



ALTHOUGH all the laws which we have deduced from the 

 kinetic theory of gases are in accordance with experiment, 

 yet it must not, on the other hand, be overlooked that the 

 agreement between observation and the strict results of 

 theory has not proved to be absolutely complete and unex- 

 ceptionable for any of the laws. In the case of Boyle's 

 law respecting the pressure we have already had to remark 

 that it holds good only approximately, and that every one 

 of the gases shows deviations from this law, which, even if 

 in most cases only small, are yet distinctly provable. This 

 remark holds good also for all the other laws which follow 

 from the theory. That Dal ton's law with respect to the 

 pressure of mixed gases suffers from the same deficiency as 

 Boyle's cannot be doubted ; from numerous observations 

 which Galitzine 1 has partly made by himself and partly 

 drawn from other sources, the pressure of a mixture is 

 sometimes greater and sometimes less than the sum of the 

 pressures exerted by the components separately. There 

 must therefore be present several causes of different kinds 

 which act together and cause the deviations from the theo- 

 retical laws in either the one direction or the other. 



Just as incompletely do the experiments on the effusion 

 of gases agree with the conclusions of theory. Neither 

 does the speed of flow, as determined in Graham's and 

 Bun sen's experiments, exactly correspond to the theo- 

 retical law, nor do the changes of temperature occur 



1 Das Dalton'fche Gesetz, Strassburg 1890 ; Wied. Ann. xli. 1890, p. 588 ; 

 Gott. Nachr. 1890, p. 22. 



