An Investigation of a Case of gradual Chemical Change. 421 



The formula embodying these results takes the same form as that 

 in Messrs. Harcourt and Esson's reaction, in which it may be remem- 

 bered the rate of decomposition doubled itself for a difference of 10 

 in temperature, whilst in our reaction it is doubled for every 5. 



The formula is thus expressed : 



where t is temperature, B rate at 0, B^ is rate at t, k is a constant. 

 The rough approximation that the rate doubles itself for 5 would 

 give k = 0-3010/5 = 0'0602. The value of k is determined from experi- 

 ment as 



log B^ log R/-5 



c "' 



and the mean of a large number of experiments gives it as about 

 0-0585. 



k is, however, not absolutely constant, but is found to vary slightly 

 with the temperature (t) for which it is determined. It is larger for 

 a low temperature range of 5, and smaller for a difference of 5 at a 

 higher temperature. In fact, speaking roughly, between and 15 

 the rate is a little more than doubled by a rise of 5 ; between 20 

 and 35 it is a little less than doubled. The following table will show 

 the amount of variation from this ratio : 



Table XVI. Values of k between 



k is thus seen to vary slightly with the temperatures between which 

 it is determined. The same secondary variation was noticed by 

 Messrs. Harcourt and Esson in their reaction. On comparing column 4 

 with column 5 it will be seen that their mean value is almost the 

 same. At present it is difficult to extricate the secondary variation 

 from experimental error, especially as a greater range of temperature 



