56 THE BEHAVIOUR OF SOLUTIONS OF HYDRIODIC ACID 



At the end of twenty-four hours on opening the stop-cock again, 

 a large quantity of oxygen was found to bubble through the 

 solution, showing that some of the oxygen there had been used 

 up during the twenty-four hours. Every day as much oxygen 

 as possible was forced into the bottles containing the solution, 

 until at the end of about nine weeks, the solution had lost all 

 its colour, with the exception of the slight peculiar colour men- 

 tioned previously. Some of the solution was drawn off and 

 tested for iodine and iodides, but 'not the least trace of either 

 was found to be present. The passage of oxygen into the solu- 

 tion was continued with the result, that at the end of another 

 week, the slight colour possessed by the solution entirely dis- 

 appeared. During this time it was roughly estimated that not 

 less than twenty-five litres of oxygen, at the ordinary tempera- 

 ture of the laboratory and a pressure somew T hat above the 

 normal, were passed into the iodide solution. 



On the foregoing grounds then, it is not unreasonable to 

 suppose that the iodine is being transformed into some oxygen 

 compound, and that this transformation is accelerated by light. 



Creighton and Mackenzie 1 have shown in the case of solu- 

 tions of hydriodic acid acted upon by radium, where the iodine 

 content .after a time begins to diminish, it is very probable it is 

 the hydriodic acid that is transformed and not the iodine itself, 

 thus lessening the content of free iodine by upsetting the equili- 

 brium between the two substances. On account of the similar- 

 ity between the two cases, it is possible that this is the manner 

 in which the cha'nge takes place here. 



The colourless solutions from which the iodine had dis- 

 appeared were now examined. It was found that these solu- 

 tions contained no iodide, but,, however, a small quantity of 

 iodate. If these solutions were allowed to stand for a few weeks 

 after becoming colourless, before testing, there could not be 

 obtained the slightest trace of iodate. These facts would seem 



1 Loo. cit. 



