50 THE BEHAVIOUR OF SOLUTIONS OF HYDRIODIC ACID 



The potassium iodide used was the chemically pure guaran- 

 teed reagent supplied by C. F. Kaulbaum. 



By carrying out the titration in the above manner, the error 

 was found to be about 0.08 cc. sodium thiosulphate solution. 



As has already been stated, the iodine in solutions of 

 hydriodic acid diminishes under certain conditions; in the case 

 where the hydriodic acid is placed in the sunlight the iodine 

 entirely disappears in time. If there was a new substance 

 being formed, it was felt that its nature could best be ascer- 

 tained from a study of the change under the action of sunlight, 

 as this was the most easy to control and by far the most rapid. 



As a starting point in this investigation, a large quantity of 

 solution was made up in the manner previously described, and 

 placed in a window where it would receive the most sunlight. 

 Portions of 50 cc. of this solution were titrated with sodium 

 thiosulphate from day to day and thus the variations in the 

 content of free iodine were established. 



On account of the reaction being a reversible one and its 

 point of equilibrium being changed bv light, the numbers i'n 

 the following table are given for the days which were of about 



the same degree of brightness. 



TABLK I. 



