338 Perkins — -Gravimetric Determination of Free Bromine. 



Art. XXYII. — The Gravimetric Determination of Free Bro- 

 mine and Chlorine, Combined Iodine, and Oxidizing 

 Beagents by means of Metallic Silver / by Claude C. 

 Perkins. 



[Contributions from the Kent Chemical Laboratory, Yale Univ. — ccix.] 



In a former paper* a method for the gravimetric determina- 

 tion of free iodine by means of metallic silver was described 

 in detail. This paper has to do with the application of the 

 same process to the determination of free bromine and chlor- 

 ine, other members of the halogen group, to the estimation 

 of combined iodine, and, indirectly, to the determination of the 

 oxidizing power of certain oxidizing reagents. 



The silver best adapted for this process is obtained electro- 

 lytically in a very finely divided state, being deposited as a 

 black mass (probably silver hydridef) upon a small moving 

 cathode. As long as the mass adheres to the electrode it 

 remains perfectly intact but as soon as it is shaken off into the 

 solution it immediately turns to a dull gray color, the hydro- 

 gen escapes, and the silver settles to the bottom in a fine flour- 

 like powder. The mass of silver hydride should not be 

 allowed to adhere to the electrode after it begins to change 

 color, as the silver then collects in a crystalline form which 

 does not absorb iodine readily. 



Determination of Free Bromine and Chlorine. 



In applying the process to the determination of bromine 

 and chlorine a definite amount of the aqueous solution of these 

 haloids was introduced into a flask containing an excess of 

 potassium iodide made acid with hydrochloric acid and the 

 whole shaken in an atmosphere of hydrogen with a weighed 

 amount of silver. The residue of silver and silver iodide was 

 collected in a Gooch crucible, washed, dried, and weighed. 

 The increase in weight of the silver should represent the 

 weight of iodine liberated from the iodide and from this the 

 amount of halogen may be easily calculated. Table I shows 

 the results of three determinations with bromine and Rve 

 determinations with chlorine in which the average error falls 

 within 0-0002 grm. 



Determination of Potassium Iodide. 



In applying the process to the determination of combined 

 iodine a definite amount of a solution of potassium iodide, 

 previously standardized by the distillation method with sul- 



* This Journal, xxviii, 33, 1909. 



f Bartlet andEice, Am. Chem. Jour., xix, 49. 



