16 THE INFLUENCE OF RADIUM ON THE 



Since for no radium at 36°C., Xj was found to be 0.70, and 

 \ was zero (or very small), we see from the foregoing 

 results that the influence of the radium at this temperature is 

 to decrease the rate of decomposition of the hydriodic acid into 

 iodine, and to increase the second action considerably, namely 

 the transformation of the iodine into the third compound. 



It is an easy matter to determine when the amount of 

 hydriodic acid is half gone. If n is the amount of hydriodic 

 acid initially present and P is th e amount present at any time 



t, then V = n e~^J*^ 



Calling T the time taken for half of the hydriodic acid to be 



transformed, we have ^ = e~ i" 



whence i = — —^ 



\ 

 Substituting the values of X obtained with no radium for 

 24''C. and SG^C. in this equation, we find that it takes about 384 

 hours at the former temperature and about 17 hours at the 

 latter for half the amount of hydriodic acid to be decomposed 

 into iodine. 



Effect of Temperature. 

 In order to show the effect of temperature alone, both when 

 the solution is under the influence of radium and without it, 

 the reaction was allowed to proceed for ten hours at various 

 temperatures. The results were as follows : 



