Chemical Attraction between Atoms from Physical Data, 87 



Suppose the curves A/' A 2 f ', B/' B 2 ", . . . ., in fig. 3 

 represent the graphs of this equation corresponding to the 



Fisr. 3. 



temperatures T lf T 2 , . . . . Let the abscise o£ the points 

 «3, 63, • • •? denote the values of p z or (p\ — P2) of a liquid in 

 contact with its saturated vapour. The ordinates of the 

 points then give the surface tension at different temperatures. 

 The equation of a set of curves which pass through the points 

 «3, h, . . ., is a formula for the surface tension. An infinite 

 number of such sets of curves can be obtained. It follows, 

 therefore, in the same way as before that the law of molecular 

 attraction deduced from surface tension data should contain 

 an arbitrary function. 



Next let us suppose that the attraction between two mole- 

 cules a given distance apart is independent of the tempera- 

 ture. Let the graph of the equation for the surface tension 

 in this case be represented by the curve A/" A 2 '", in fig. 4, 

 the points a z , fe 3 , . . ., having the same meaning as before. 

 The equation of the surface tension of a liquid in contact 

 with its saturated vapour is the equation of the curve through 

 the points a 3 , 6 8 , . . . . Now this equation can be approxi- 

 mately found by trial or by the help of the Calculus of Finite 



