i 4 PHYSICAL PROPERTIES AND COMPOSITION 



We will therefore confine ourselves to gases and liquids, 

 and further, to those properties which are more or less 

 directly connected with the characteristic equations. Since 

 we adopt these equations as basis it should be remarked 

 that we are here dealing with physical relations of a dif- 

 ferent order to those previously used. In dynamics it was, 

 on the physical side, mainly the two fundamental laws of 

 therm o-dynamics ; in statics the limit-laws of Boyle, Gay- 

 Lussac, and Avogadro were invoked, and they may claim 

 strict applicability at least to the state of infinite dilution 

 as gas or solution. The characteristic equations, on the 

 other hand, are merely more or less rationally founded 

 interpolation formulae, which are only strictly in accord 

 with the facts for the state of infinite dilution, and then 

 resolve themselves into the former laws. As a consequence 

 of this the treatment following must be essentially dif- 

 ferent. Whilst the fundamental laws of thermo-dynamics, 

 and the limit-laws for infinite dilution serve to control 

 experimental results, here, on the contrary, an accepted 

 relation must often be modified to suit the facts, yet mostly 

 in such a way that something of it remains which could 

 not so easily be made out from the facts alone. From this 

 again follows the essential point that the relations obtained 

 on account of their partly empirical character only allow 

 of conclusions as to molecular weight and constitution, 

 inferior in certainty to those of Part II. 



i. VOLUME KELATIONS. 



Since in dealing with volume relations we are concerned 

 with the relations to chemical constitution, we will adopt 

 a corresponding arrangement, and first consider the rela- 

 tions which depend on the number of molecules, called by 

 Ostwald colligative, and which may serve as a guide to 

 determining molecular weights. Afterwards will come the 

 additive and constitutive relations, which depend on the 

 composition of the molecule. 



