THE 

 LONDON, EDINBURGH, and DUBLIN 



PHILOSOPHICAL MAGAZINE 



AND 



JOURNAL OF SCIENCE. 



[FOURTH SERIES.] 



OCTOBER 1874. 



XXXIV. On Gladstone's Experiments relating to Chemical Mass. 

 By Edmund J. Mills, D.Sc., F.R.8* 



I. nnHE Philosophical Transactions for 1855 (vol. cxlv.) con- 

 JL tains an important memoir by Gladstone " On Circum- 

 stances modifying the Action of Chemical Affinity." In this 

 memoir numerous sets of experiments are described^ which 

 mainly serve to determine, by means of an increase or diminu- 

 tion of colour, the progress of certain selected reactions. The 

 results are exhibited in curves, several of which show a regular 

 course, while all are continuous ; but no mathematical expres- 

 sion of the law of action is given. About eleven years after- 

 wards (Phil. Trans. 1865-6) it was shown by Esson, on the 

 basis of Harcourt's experiments, that when a substance under- 

 goes chemical change, the residue y of changing substance is 

 connected with the unit intervals x of change (time, reagent, or 

 other operator) by the equation 



y = ae~ a *, 



where a represents the amount of substance originally present, 

 and « the amount of it disappearing per unit of x. This relation 

 is graphically represented as a logarithmic curve ; but, as a rule, 

 even in very simple cases, its expression is more complex, and 

 corresponds to the form 



y — a^-^ + a^e-^ 1 ', 



which indicates that two bodies are undergoing change, or that 

 one body is undergoing dual change. In either case the amount 



* Communicated by the Author. 

 Phil. Mag. S. 4. Vol. 48. No. 318. Oct 1874 11 



