UNPUBLISHED FKAGMENTS. 425 



In case of one molecular formula in liquid and none in gas, we 

 may give the molecules repelling forces which will make the gas 

 possible. (?) [See p. 417.] 



Deduce Ostwald's law in more general form. 

 Deduce interpolation formula. 



What use can we make of Latent Differences? // A , /Z AA , /Z B , yu BB , 

 /X AB all conform to law, I think. 



[On the Equations of Electric Motion.] 



[A somewhat abbreviated copy of a letter written four years earlier 

 (in May 1899) to Professor W. D. Bancroft of Cornell University Jwd 

 been placed by Professor Gibbs between the pages of the manuscript, 

 and was evidently intended to serve as a basis for the chapter " On 

 the equations of electric motion " mentioned in the list on page 418. 



Through the courtesy of Professor Bancroft the original letter has 

 been placed at the disposal of the editors and is here given in full. 

 The major portion of this letter was incorporated by Professor 

 Bancroft in an article entitled " Chemical Potential and Electro- 

 motive Force" published after the death of Professor Gibbs, in the 

 Journal of Physical Chemistry, vol. vii.,p. 416, June 1903.] 



My dear Prof. Bancroft : 



A working theory of galvanic cells requires (as you 

 suggest) that we should be able to evaluate the (intrinsic or chemical) 

 potentials involved, and your formula 



is all right as you interpret it. I should perhaps prefer to write 



At 





logy D , (1) 



At 

 or yvdp^dyv, (2) 



for small values of y D , where y D is the density of a component (say 

 the mass of the solutum divided by the volume of the solution), M^ its 

 molecular weight (viz., for the kind of molecule which actually exists 



(1DV A \ 

 t~MJ' an( * ^ a 



quantity which depends upon the solvent and the solutum, as well as 

 the temperature, but which may be regarded as independent of y D so 

 long as this is small, and which is practically independent of the 

 pressure in ordinary cases. 



