Gooch and Ensign — Determination of Bromine. 145 



Art. XYI. — The Direct determination of Bromine in mix- 

 tures of alkaline Bromides and Iodides ; by F. A. Gooch 

 and J. R Ensign. 



[Contributions from the Kent Chemical Laboratory of Yale College. — IV.] 



In a recent paper from this laboratory* two methods were 

 elaborated for the direct determination of chlorine in mixtures 

 of alkaline chlorides and iodides. These methods are based upon 

 the action of oxidizing agents, in presence of free sulphuric acid, 

 upon dilute solutions of the haloid salts at the boiling tempera- 

 ture. Under conditions properly controlled, iodine is entirely 

 eliminated by volatilization, leaving the chlorine combined and 

 undisturbed. In the work of which this paper is an account 

 we have endeavored to determine the applicability of the same 

 reactions to the separation of bromine from iodine in similar 

 association. It appeared very early in the work that the exact 

 conditions which were found suitable in the separation of 

 chlorine and iodine are inappropriate to the separation of bro- 

 mine and iodine. Thus, while according to one of the two 

 methods which we discuss, the gas evolved from 2 grms. of 

 sodium nitrite, passed into a solution containing in 400 cm : ' 0*5 

 grm. of potassium chloride, 1 grm. of potassium iodide, and 5 cm 3 

 of strong sulphuric acid, eliminated the iodine with a mean error 

 of 0*0002 grm. +, and while according to the other process the 

 iodine was removed by the action of 2 grms. of ferric sul- 

 phate and 3 cm 3 of nitric acid upon a solution similarly 

 constituted otherwise with a mean error of 0*0001 grm., it 

 was found that like conditions in certain experiments in which 

 potassium bromide replaced the chloride were productive 

 of errors amounting to from 0*0100 grm. to 0*0200 grm. in 

 both processes. It was evident, therefore, that the reactions 

 which obtained in these processes must be carefully studied 

 and adjusted to make them applicable to the separation of bro- 

 mine and iodine. Attention was turned at the outset to the 

 behavior of the bromide taken by itself — that is, unaccom- 

 panied by an iodide — in boiling solutions containing the rea- 

 gents of the process. Measured portions of solutions of po- 

 tassium bromide and of the other reagents were brought to 

 definite volume and boiled in a distillation flask connected with 

 a condenser. The measured distillate was treated with silver 

 nitrate after the addition of a few drops of sulphurous acid to 

 convert free bromine to hydrobromic acid, and, after the ad- 

 dition of an excess of nitric acid to dissolve precipitated sul- 

 phite, the silver bromide was settled, filtered off upon asbestos 

 in a perforated crucible, dried and weighed. The details of 

 these experiments are given in the accompanying tabular state- 

 ment. 



* Gooch and Mar, this Journal, xxxix, 293. 



Am. Jour. Sci.— Third Series, Vol. XL, No. 236.— August, 1890. 

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