394 Prof. R. Clausius on the Behaviour of Carbonic Acid 



of a different kind from those found by Regnault. That is to 

 say, while Regnault had found that, with all the gases ex- 

 amined by him, the pressure increases more slowly than the 

 density, in batterer's experiments it turned out that with very 

 great pressure the case is reversed, and the pressure increases 

 more quickly than the density : with air, nitrogen, and car- 

 bonic oxide gas the pressure already reached an amount of 

 about 3000 atmospheres when the density had only become 

 from 700 to 800 times that which exists under the pressure of 

 one atmosphere. 



Upon the causes on which these deviations of the gases 

 from Mariotte's and Gray-Lussac's law depend, in my treatise 

 " Ueber die Art der Bewegung, welche wir Warme nennen"*, 

 I expressed myself as follows : — 



" In order that the law of Mariotte and Gray-Lussac, and 

 the laws in connexion with it, may strictly hold good, the gas 

 must, as regards its molecular state, satisfy the following con- 

 ditions : — 



" (1) The space actually filled by the molecules of the gas 

 must be vanishingly little in comparison with the entire space 

 taken up by the gas. 



" (2) The time of a collision (i. e. the time required by a 

 molecule, when it strikes against another molecule or a solid 

 obstacle, in order to alter its motion in the manner in which 

 it is altered by the collision) must, in comparison with the 

 time which elapses between two collisions, be vanishingly 

 short. 



" (3) The influence of the molecular forces must be vanish- 

 ingly little. This implies two things. In the first place, it is 

 required that the force with which all the molecules at their 

 mean distances attract each other vanish in comparison with 

 the expansive force arising from the motion. But the mole- 

 cules are not always at their mean distances from one another ; 

 often in the course of the motion one molecule comes into the 

 immediate vicinity of another or of a solid obstacle likewise 

 consisting of operative molecules ; and at such moments the 

 molecular forces of course come into action. Hence the second 

 requirement is that those parts of the path described by a 

 molecule on which the molecular forces have an influence, 

 perceptibly altering the motion of the molecule in direction and 

 velocity, vanish when compared with the portions of the path 

 on which the forces can be regarded as inoperative. 



" If these conditions are not fulfilled, deviations in various 

 directions from the simple law of the gases take place, which 



* Clausius, Pogg. Ann. c. p. 358 (1857) ; and Abhandlungensammlung, 

 ii. p. 235. 



