the Unit-Stere Theory. 349 



than at the critical points themselves. Octane ceases to be 

 divergent. 



(4) Just as the additive law is very approximately true at 

 equal reduced pressures, so also is the law o£ corresponding 

 states. This is especially shown when the volumes at the 

 equal reduced pressure '002949 are taken as standard instead 

 of the molecular critical volumes. 



(5) At Corresponding Jemperatures. — The laws fail some- 

 what under conditions of equal reduced temperature. The 

 departure from the law of additivity is in the same direction 

 as that from the law of correspondence and is proportional 

 to it. 



This shows that i£ the one were true under the above 

 conditions, the other would be also. 



It may be demonstrated that the condition for the validity 

 of the laws of additivity and correspondence depend, not on 

 the ratio T/T K , but en the difference T K -T. T K -T may not 

 be always quite the same for the different members of a series 

 of homologues, as we pass from one condition to another, but 

 often is so, the complex normal paraffin hydrocarbons near 

 their melting-points being a case in point. 



T 



(6) The critical coefficients ^ of Guye, being subject to 



K 



similar additive relations to those of the molecular critical 

 volumes, are approximately proportional to the valency 

 numbers of the compounds. 



(7) The apparent volumes of the liquid hydrocarbons from 

 pentane to octane under conditions of equal reduced pressure 

 are approximately equal multiples of their molecular re- 

 fractions as calculated from the Lorenz and Lorentz 

 formula. 



It thus follows that the molecular refractions are similarly 

 subject to the valency law. 



The above relations seem to be strongly in favour of the 

 view that valency is a volume property, and also that the 

 laws of additivity and correspondence are very closely related. 



The validity of the law of correspondence for liquids has 

 hitherto been supposed accounted for by Van der Waals' 

 theory. 



The law of additivity, however, does not appear to be 

 deducible from Van der Waals' equation of condition. 



It is further remarkable that both laws are far more strictly 

 followed under conditions such that the assumptions upon 

 which the above theory is based are less likely to be valid 



Phil. Mag. S. 6. Vol. 14. No. 81. Sept. 1907, 2 B 



