I. EELATIONS BETWEEN PHYSICAL 

 PBOPERTIES AND COMPOSITION 



IN dealing with physical properties with regard to their 

 relations to composition, a preliminary study is needed in 

 order to refer the property in question, so far as the body 

 under consideration is concerned, to one or more constant 

 quantities. If we take as example the state of aggregation, 

 it is obvious that the boiling point is not such a constant 

 quantity. On comparing benzene with ethyl alcohol : 



Boiling point under 222 mm. under 2256 mm. 



Benzene 45 120 



Ethyl alcohol 50 106 



we find that the difference of boiling points even changes 

 sign through change of pressure, as at low pressure alcohol, 

 at high pressure benzene, has the higher boiling point. 



Before any relation can be found between boiling point 

 and composition, then, that between boiling point and 

 pressure must be explained, so that the preliminary study 

 referred to appears in general as the relating of the pro- 

 perty considered to its circumstances. 



Such a preliminary study has hitherto only been 

 partially carried out in the form of the so-called charac- 

 teristic equation, and that only for amorphous, i. e. for 

 liquid and gaseous states. In crystalline bodies the orien- 

 tation of the substance involves complications that have 

 retarded the solution of the problem, which even for 

 amorphous bodies has only been given very imperfectly. 



