L 805 ] 



XXXVI. On the Laio of Molecular Force. 

 By William Sutherland, M.A., B.Sc* 



IN the Philosophical Magazine for August 1886, and July 

 and August 1887, I advanced the hypothesis that the 

 law of molecular force is that of the inverse fourth povrer of 

 the distance, and considered how far its consequences har- 

 monize with the results of the experiments of Thomson and 

 Joule on the expansion of gases through porous plugs, and 

 "odth the experiments of Amagat and Andrews on the volume 

 occupied by CO2 at different temperatures and pressures. In 

 the present paper I shall discuss the same law in the light of 

 the recent beautiful discoveries of Eotvos and Robert Schiff 

 in capillarity, and shall show, as the chief result of the inquiry, 

 the following law of the parameter A in the expression 3Am^/r^, 

 which expresses the force between two similar molecules of 

 mass m at distance r apart, the law of their mutual potential 



T . A?/i2 

 bemo- 5—. 



In compounds containing C, 0, and H the molecule may 

 be considered to have a volume, to which each atom of H 

 contributes an amount very small in comparison with that 

 contributed by an atom of and of C ; while an atom of 0, 

 when singly bound to another atom, contributes an amount 

 equal to that of two carbon atoms, and when doubly bound 

 equal to that of three carbon atoms. The volume of such a 

 molecule can then be expressed in terms of that of a carbon 

 atom, and the jycirameter A varies inversely as the surface of the 

 molecule. 



By the volume of a molecule I do not mean what is usually 

 called the molecular volume (an objectionable term, which I 

 would propose to replace by the term molecular domain), but 

 the actual volume of the molecule. Another result of the 

 investigation will be to show that the rate of change of the 

 translatory kinetic energy of nearly all liquid molecules with 

 temperature is the same when measured at low constant 

 pressure. 



Eotvos (Wiedemann, xxvii.) announces the following remark- 

 able law : — The rate of variation with temperature of the 

 product of the surface-tension of a liquid by its molecular 

 domain raised to the power two thirds, is the same for all 

 liquids ; or, in symbols, if a denote surface-tension, and v 

 molecular domain, 



I (».») = -227. 



* Communicated by the Author. 



Phil. Mag. S. 5. Vol. 27. No. 167. April 1889. X 



