110 Messrs. A. V. Harcourt and W. Esson. [May 9, 



upon temperature, and of the experiments recorded in a previous 

 paper, made to determine the law of variation of the rate of change 

 with iodide, shows that when the ratio of the numbers of HCl and HI 

 is higher than it is in the set quoted above, the value of the increment 

 per unit of chloride per unit of iodide falls to 16'2 X 10~ 6 . This lower 

 value is the same for values of the number of HCl, ranging from 190 

 to 547, and for values of the ratio of the numbers of HCl and HI, 

 ranging from 20 to 210. 



The formulae for in these two cases in a solution containing in 

 1 c.c. 1 HI and c HCl are at a temperature of 30. 



(1.) a= (1345 + 16'8 c) 10- 6 , 

 (2.) = (1230-t-16'2c)lO- 6 . 



Variation of Iodide. 



It was shown in a previous paper that when quantities of iodide 

 are introduced into the medium sufficiently small in amount, in com- 

 parison with other substances not participating directly in the 

 reaction, the rate of chemical change varied directly with the amount 

 of iodide. It was conjectured that when the amount of iodide is 

 large enough to modify considerably the character of the medium, it 

 would have the same kind of effect upon the reaction as hydrogen 

 sulphate and hydrogen chloride. It is now shown that the increment 

 of the rate per unit of hydrogen iodide per unit of iodide is 19'4 x 10" 6 

 at a temperature of 30, the rate with 1 HI at the same temperature 

 being 1210 x 10" 6 . The formula for the rate with iHI is 



It will be observed that the actual rate with unit of hydrogen 

 iodide in a medium consisting of water and hydrogen iodide is 

 approximately the same as the theoretical rate with unit of iodide in 

 a medium consisting of water, hydrogen iodide, and either hydrogen 

 sulphate or hydrogen chloride when the ratio of the numbers of 

 JEPSO 4 and HI and of the numbers of HCl and HI exceeds 20. It 

 has been shown above that this rate is 1230 X 10" 6 . 



Variation of Sodium Hydrogen Carbonate. 



In a medium, consisting mainly of water and sodium hydrogen 

 carbonate the increment of the rate per unit of NaHCO 3 per unit of 

 iodide is 40 x 10~ 6 at a temperature of 15, the formula for the rate 

 with 8'59 JVaJand quantities of the carbonate ranging from 25 NaRCO 3 

 to 227 NaHCO\ being at this temperature 



a. = 8'59 [ 132 + 406 }10- 6 . 



