( 199) 

 If th(j whole (iiiantity of the substance is equal to the molecular 



weiyiit, Cy =: — - , so that tlie cijuality ot' i'u(l -h")(^~~^') '"ii.v be written 



or 



(1 + a) (1 -b) (1 + a) (I - Ö') 



The nuautitv is the normal density, which would 



J ' (1+r.) {\-h) 



also have been found at 0°, if the law of Boyle had been true. 



Let us represent it by </« . 



If we determine the density of a gas at 0° and under the pressure 

 ;<(, (at which the quantities a and b have been determined), we have 

 only to divide this density by (1 -{-a) (1 — ^), to find the normal 

 density, and to this the molecular weights are proportional. 



If the density is determined at another temperature and under 

 another pressure, a volume t'o' is calculated from the pressure, the 

 temperature and the volume read, making use of the formula: 



p V 



1 +«« 



Bv means of this volume a density (</„)' = — is fouml, and we 



have to investigate in what proportion it stands to d„ . 



Let us calculate for this purpose tlie proportion of t'g and v^' , 

 From 



Po I'o (1 + «) (1 — ^) (1 + "0 « Po ^0^ 



P = 7 5— 



V — b Vq V 



follows 



(1 + a) (1 - b) V 



** 1 + «t />o -^ % — 6 1'o l+ca " V 



or 



t'n ' V I I ~\- at V 



If we restrict ourselves to very large volumes only, so to obser- 

 vations under a small pressure, we may put 



14 



Troceediugs Kojal Acad. Amstevdaiu, Vol. I. 



