PROGRESS IN PHYSICAL CHEMISTRY 



DURING 1894. 



Part I. 

 CONTINUITY OF GASEOUS AND LIQUID STATES. 



T/ AN der Waals Theory. — In connection with the theory 

 of liquids and gases the most important communi- 

 cation from a physico-chemical point of view is due to 

 Young (1), who tests the validity of van der Waals' theory 

 of corresponding states in the case of some twenty-two 

 well-defined and carefully purified substances. It is now 

 beyond question that van der Waals' equation is but an 

 approximation, and although Bakker (2) has deduced it 

 from thermodynamical principles, Amagat's recent work 

 (3) again shows that even in the case of compressed gases 

 it is too simple. De Heen and Dwelshauvers-Dery (4) 

 furnish similar evidence, as they find that, in order to make 

 the equation satisfactorily reproduce Amagat's isothermals, 

 different values have to be given to both constants at 

 different temperatures. Although this is so, Young's work 

 proves that in certain cases the theory is in surprising 

 accord with the facts, and the results are of especial 

 interest, as they indicate that the chemical nature of the 

 substance must be considered in investigations of this kind. 

 It follows from van der Waals' reduced equation of 

 condition that if the pressures of different substances are the 

 same fraction of their critical pressures, then their boiling- 

 points on the absolute scale should be the same fraction of 

 their absolute critical temperatures, and the volumes of the 

 saturated vapours or of the substances as liquids should be 

 the same fraction of their critical volumes. The liquids used 

 fall into lour groups. Group I. contains benzene and its 

 monohalogen derivatives, carbon tetrachloride, stannic 

 chloride and ether; Group II., the three lowest fatty 

 alcohols; Group III., acetic acid; and Group IV., the ten 



lowest fatty esters. The members of Groups I. and IV. 



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