( 605 ) 



in this area. Therefor wc compare the experimental equation of' 

 state of" a substance Jiear the critical [)oint liquid-gas with an 

 equation oi' state which we shall call the special undisturbed equation 

 of state for tluit substance and which is derived by adjusting- 

 interpolation formulae to observations in areas where no disturbances 

 occur such as in the neighbourhood of the critical point. 



For we presume to be able to deri\e from the results of data 

 at our disposal that the experimental equation of state differs from 

 the special undisturbed one by the presence of terms which for 

 the accuracy reached iji the observations meant only deserve notice 

 in the neighbourhood of the critical point, and which are intimately 

 connected with the great compressibility in this area. We shall call 

 the compound of these terms the disturbance function in the equation 

 of state in the neighbourhood of the critical point. 



In order to be able to derive from the special undisturbed equation 

 of state and the disturbance function at the critical state the con- 

 ditions of coexistence, vapour pressures, liquid and vapour densities, we 

 must have investigated whether iji that condition Maxwell's criterium 

 for a substance consisting of one component may be applied nnmo- 

 ditied or not. 



For the present we must include in this disturbance function the 

 disturbances caused by admi^ctures which chemically may have an 

 existence of their own, hut which it was not possible to remove 

 and which always occur in definite quantities, as long as the nature 

 and the quantity of these admixtures are unknown. The investigation 

 of substances with small quantities of admixuire ^) may help us 

 towards a better judgment of the question whether this disturbance 

 function may be entirely ascribed to admixtures which may exist 

 separately. As long as this has not yet been decided it will be 

 indispensable to pay regard also to admixtures which can have no 

 existence of their own but which may always occur as electrically 

 charged particles, or as portions of the substance of greater density 

 which may give rise to differences of density distributed as nebulous 

 drops and which in this area might be kept up by capillary force. 

 It will also be necessary to take into account differences of density 

 depending on the statistic equilibrium. 



In order to arrive at some knowledge of such a disturbance 



1) Comp. p. 604 note 3. For tlie influence of small quantities of admixture of sub- 

 stances of small volatility the following investigations are important : M. Gentnerszwer, 

 ZS. physik. Chemie 46 (1903) Ostwald Jubelb. p. 427, 61 (1907) p. 356; 

 M. Centnerszwer and A. Pakalneet, ibid, 55 (1906) p. 803, M. Gentnerszweh and 

 A. Kalnin, ibid. 60 (^1907; p. 441. 



