On the Separation of Chlorine, Iodine and Bromine. 145 



the action of chlorine at an elevated temperature, yet chloride of 

 silver is completely decomposed by bromide of potassium, and both 

 the bromide and chloride of silver by iodide of potassium. Even 

 the action of hot strong hydrochloric acid has but little influence 

 upon the iodide of silver ; many days of continuous boiling 

 are necessary for its entire decomposition. I believe that it has 

 been the opinion of chemists that chlorine possesses an affinity for 

 silver superior to all other elementary bodies, and we are told in 

 Gmelin's Handbook that all salts of silver, even the insoluble ones, 

 are converted into chloride by solutions of metallic chlorides. From 

 the following experiments it appears to me that bromine has a 

 greater affinity for silver than chlorine, and iodine a still greater 

 affinity than bromine. 



When a mixed solution of bromide of potassium and chloride of 

 sodium is added gradually to a solution of nitrate of silver, not in 

 excess, no trace of chloride of silver is precipitated, as long as any 

 bromide remains in solution. 



If to a similar solution, iodide and bromide of potassium and chlo- 

 ride of sodium be added, iodide of silver and nitrate of potassa are 

 formed, the bromide of potassium and chloride of sodium remaining 

 undecomposcd. 



When bromide of potassium is poured upon chloride of silver, an 

 entire decomposition ensues, bromide of silver and chloride of potas- 

 sium being produced. 



When iodide of potassium is added to chloride of silver, iodide of 

 silver and chloride of potassium are formed; and when iodide of 

 potassium is added to bromide of silver, there is a similar decom- 

 position, the iodine replacing the bromine. 



When chloride of silver in excess is agitated with a solution of 

 iodide of potassium and warmed for some hours, no trace of iodine 

 can be detected in the solution : when however chloride of sodium is 

 poured upon iodide of silver, no decomposition occurs, neither is 

 there any action upon bromide of silver with the same salt : and 

 when bromide of potassium is added to iodide of silver, there is no 

 alteration in the union of the elements. 



From a number of experiments made in illustration of the pre- 

 ceding statements, I deemed it possible that the separation of chlo- 

 rine, bromine and iodine could be accomplished by this reaction. 



The method which I have devised is simply this : After weighing 

 three equal portions of the salts to be analysed, they are placed in 

 three flasks with ground-glass stoppers, and about an ounce of water 

 is added to each ; nitrate of silver being then added, slightly in ex- 

 cess, to the three, the stoppers are replaced, and each flask agitated 

 violently. The precipitates subside in a few minutes, leaving the 

 supernatant liquid perfectly clear. They are then fdtered through 

 separate funnels, and washed with hot water. No. 1 is dried and 

 weighed. No. 2 is digested in bromide of potassium, dried and 

 weighed ; and No. '.i in iodide of potassium, dried and weighed. 



To test the method, a mixture was made of fj grains of iodide of 

 potassium, .0 grains of bromide of potassium, and 5 grains of chlo- 

 Phil. May. S. 4. Vol. 15, No. 08. Feb, 1858. L 



