54 THE BEHAVIOUR OF SOLUTIONS OF HYDRIODIC ACID 



The potassium hydroxide solution from the U-tubes was 

 diluted to 200 cc. 45 cc. of this solution were acidified and 

 titrated with ^ sodium thiosulphate solution, of which 1.53 cc. 

 were required to remove the blue colour due to the iodine. From 

 this data it may be shown that the 200 cc. of hydroxide, there- 

 fore, contain 0.0864 grain of iodine. Only one-sixth of this 

 iodine was present as iodate in the potassium hydroxide solu- 

 tion, that is 0.0144 gram. The quantity of iodine as iodide 

 was estimated by oxidising it to iodate by means of potassium 

 permanganate solution; 1 cc. of this solution = 0.00 5 6 gram of 

 permanganate. 25 cc. of the solution of potassium hydroxide 

 which had been diluted to 200 cc. was acidified slightly with 

 sulphuric acid and then made alkaline with potassium carbon- 

 ate. The permanganate solution was then added until the 

 liquid became slightly pink. In this titration 4.40 cc. of the 

 potassium permanganate solution, corresponding to 0.0246 gram 

 of potassium permanganate, were required to oxidise the iodine. 

 It will readily be seen that this amount of potassium perman- 

 ganate has been used in oxidizing 0.0098 gram of iodine. 

 Therefore, the amount of iodine in the potassium hydroxide 

 solution as iodide was eight times this amount, or 0.0784 gram. 

 Hence, the total amount of iodine lost by evaporation- from the 

 iodine solution and absorbed by the potassium hydroxide solu- 

 tion was, 



0.0144 gram iodine as iodate 

 0.0784 " " iodide 



0.0928 " absorbed. 



In this experiment 300 cc. of iodide solution (cone. 1 gram 

 per litre) which contained 0.2293 gram of iodine, were used, 

 From these numbers it will be seen that the loss by evaporation 

 was 40.47 per cent., which leaves still sixty per ce'nt. to be 

 accounted for. 



Before leaving this experiment it would be w r ell to mention 

 hero that after all the iodine had disappeared from the solution 





