An Investigation of a Case of gradual Chemical Change. 419 

 Table XIII. 



Here we have a series in which the rate increases distinctly with 

 the amount of iodide, and it is not far from an arithmetical pro- 

 gression, certainly within the limits of experimental error. The 

 establishment of this relation would of course show that the varia- 

 tion of potassium iodide has the same sort of influence as any neutral 

 salt, and one would therefore class it with potassium chloride in this 

 investigation. On the other hand, it seems evident that the cases are 

 not exactly parallel ; double decomposition between this salt and 

 hydrogen chloride must go on, with a production of potassium 

 chloride and hydrogen iodide. The hydrogen chloride present is 

 decreased by a quantity equivalent to the amount of potassium chlo- 

 ride produced, and the hydrogen iodide produced will have its 

 specific influence different from that of the former acid. At any rate 

 one cannot be surprised at not) finding the progression quite as well 

 marked here as for potassium 'chloride. 



We will now turn to the results obtained by varying the tempera- 

 ture at which we made observations. This was done in the manner 

 described in the introduction. 



Variation in Temperature. 



The temperature at which most of our experiments were conducted 

 was 20 C. We found any variation in temperature had a marked 

 effect on the rate. A rise of temperature of 5 practically doubled 

 the rate of decomposition, and a fall in temperature of 5 halved the 

 rate at any point. In general if the temperature was varied in 

 arithmetical progression the rate varied in geometrical progression. 

 The following tables illustrate this fact : 



