PREFACE 



THE pre8ent work on ' Relations between Properties and 

 Composition ' reproduces the lectures I gave in the Winter 

 and Summer Sessions 1898-99 at the University of Berlin, 

 under the title ' Selected Chapters in Physical Chemistry.' 

 It follows, as third and last section, the first and second on 

 ' Chemical Dynamics ' and ' Chemical Statics ' respectively, 

 but is arranged as far as possible independently and covers 

 the relations of physical and chemical properties to con- 

 stitution, only with certain limitations. Some of these 

 relations are exact, and available for determining con- 

 stitution itself : these belong properly to Part II. Others 

 have at present a character so decidedly empirical that they 

 belong rather to systematic chemistry. 



Hence in the region of physical properties I have dealt 

 only with what can directly or indirectly be brought into 

 connexion with the characteristic equation. Although this 

 does not afford a strictly trustworthy physical basis, like 

 Thermodynamics in Part I and the limit-laws for the dilute 

 state in Part II, still the point of view brings out many 

 approximate regularities. 



In the relations between chemical properties and con- 

 stitution I have mostly restricted myself to those properties 

 that can easily be reduced to numerical expression. 



The fact that the first part of these lectures has already 

 been translated into French and English may serve as a 

 recommendation to this last part. 



It is, finally, a pleasant duty to express my warmest 

 thanks to Drs. W. MeyerhofFer and J. J. van Laar for the 

 revision and emendation of this work. 



J. H. VAN 'T HOFF. 



CHA BLOTTENBURG , 



December, 1899. 



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