DECOMPOSITION OF HYDRIODIC ACID. CREIGHTON. 15 



At tliis temperature it is seen that the inaximura is quickly 

 reached in the case of the solution under the influence of the 

 radium ; and the effect due to the second reaction, the supposed 

 changing of the iodine into a third substance, is soon noticeable. 

 On the other hand, the curve for the solution not affected by 

 radium resembles the curves for both radium and no radium at 

 lower temperatures, but it would seem probable that in this 

 case the time taken to reach the maximum is shorter. In this 

 case also there is therefore no measurable formation of the 

 third product. A comparison of the no radium curves for 12<*, 

 24* and 3b°C will show that witli a rise in temperature the rate 

 of decomposition of hydriodic acid increases, while the maximum 

 amount of iodine in solution is less and the time taken to reach 

 this maximum shorter. The same is true for the radium curves 

 at 12° and 24°C. 



If the theory previously stated of what is taking place be 

 correct, the general equation (1) should be the equation of the 

 radium curves for 36°C. 



Rutherford^ has shown that the smaller of the two quanti- 

 ties \i and ^2 is given by the latter part of the downward curve. 



The equation of this part of the curve is then of the form 



_Xt 

 2/ = n • e (4) 



Accordingly, from the observed values of y at 12, 16 and 27 

 hours, n was found to be 3.3 and Xi to be 0.06. By finding the 

 difi'erential of equation (1) with regard to time and equating it 

 to zero, we find that the maximum occurs at a time T, given by 



the equation 



— A.,t _- — A..,t ,„. 



iC ^ -Xo e - (£)) 



Putting for t the value 6.6 found from the curve, and for 

 \ its value 0.06, we find \., to be O.ol. The numbers calcu- 

 lated from equation (1) with these values of the constants are 

 given in the last column of Table V, and the agreement with 

 the observed values falls well within the limit of experimental 

 error. 



1. Loo. cit., p. 3i3. 



