50 



THE HKIIAVIOUR OF SOLUTIONS OF HYDHIODIC ACID 



The potassium iodide used was the clicniically pure guaran- 

 teed reagent supplied hy C. F. Kaulbauui. 



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

 was found to l»e about ± 0.08 cc. sodium thiosulphate solution. 



As has already been stated, the iodine in solutions of 

 hvdriodie. acid diminishes nnder certain conditions; in the case 

 where the hydriodie acid is ])la('ed in the sunlight the iodine 

 entirely disappears in time. If there was a new substance 

 being formed, it was felt that its natin'e could best be ascer- 

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

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



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

 solution was nnide up in the manner previously described, and 

 placed in a window where it wouhl 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 lieiug a reversible one and its 

 point of equillbi'ium being changed l)v light, the numl)ers in 

 the f(jlIo\ving table are given for the <biys which were of about 

 the same degree of briglitness. 



'I'abi.k I. 





No of cc. of j-^^o NroSmO- 





No. of cc. of ^^jji NajSjOj 



Time in 



solution required in titra- 



Time in 



.solution re(|uired in titra- 



hours. 



tion when the decomposition 



hours. 



tion when the decomposition 





of hydriodie acid tai<es place 





of lij-driodic acid takes place 





in sunlight. 





in sunlight. 



24 



46.31 



552 



20.42 



72 



58.42 



720 



18.. 55 



120 



64.42 



840 



16.62 



144 



58.93 



888 



14.26 



189 



52.14 



960 



11.80 



236 



49.97 



1056 



10.74 



288 



45.14 



1152 



6.41 



408 



44.12 



1272 



3.12 



456 



2S.55 



1.368 



0.46 



504 



23.41 



1.392 



0.00 



