1895.] Conditions of Chemical Change and its Amount. Ill 



The rate with 1 Nal and bNaHCO* is 



so that the theoretical rate with 1 Net/ only, in this medium, is 155 x 10~ 

 at a temperature of 15. At the same temperature the actual rate 

 with 1 HI in a medium consisting of water and hydrogen iodide is 

 356 x 10" 6 , a rate more than twice as great as the corresponding rate 

 with the neutral iodide. The increment of the rate per unit of 

 carbonate per unit of iodide is more that four times the highest 

 increment per unit of sulphate per unit of iodide at the temperature 

 of 15. 



Variation of Potassium Iodide, Sodium, Iodide, and Sodium Chloride, in 

 a medium consisting mainly of Water and Sodium Hydrogen 

 Carbonate. 



In this medium at a temperature of 15, the increments of the rate 

 per unit of these substances per unit of iodide are (1) for the range 

 10 KI to 30 KI, 4-15 xlO- 8 ; (2) for the range 10 Nal to 30 Nal, 

 4-84 X 10- 6 ; (3) for the range 1 NaCl to 14 Nad, 27'7 x 10-. In this 

 medium sodium chloride has a considerable effect on the rate, but in 

 a medium consisting of water and hydrogen chloride its effect is 

 almost nil. 



General Conclusion as to the effect of the Medium upon the reaction. 



Each constituent of the medium produces an effect on the rate of 

 change of unit peroxide and unit iodide, proportional to the mass, 

 and varying with the nature of the constituent. The increment of 

 this rate per unit mass of each constituent is constant so long as the 

 quantity of the predominant constituent present in the medium is 

 sufficiently large, in comparison with the other constituents of the 

 medium, to render the media in successive experiments practically 

 homogeneous. For example, when the ratio of the numbers of H*SO* 

 and HI in the medium exceeds 20 the formula for the rate at a given 

 temperature is 



a being the theoretical rate with unit of HI, b the increment per unit 

 of hydrogen iodide per unit of iodide, and d the increment per unit of 

 hydrogen sulphate per unit of iodide. If the ratio falls below 20 the 

 formula ia 



a. = i{o + 6'(t 



in which 6' and d' depend upon the relative masses of sulphate and 

 iodide present in the medium. 



YOL. LVIH. K 



