266 H. I. Cole — Estimation of Iodine and B 



rominc tn 



added to an excess of iron covered with distilled water, 

 decanting the solution from the excess of iron when the 

 color of iodine had vanished, adding the remainder of 

 the iodine, pouring the filtered solution slowly into boil- 

 ing water, to which the exact amount of acid potassium car- 

 bonate necessary to combine with the iodine had been added, 

 and filtering off the magnetic oxide of iron thus precipitated. 

 The solution of potassium iodide thus made, very faintly 

 alkaline and entirely free from chlorine and bromine, was 

 evaporated and recrystallized and the resulting salt carefully 



Fig. 1. 



ground in a mortar to insure a homogeneous product. This 

 preparation gave by the arsenate method in three determina- 



tions, 



0-4994 grm. 



0-4994 grm. 



0-4993 grm. of potassium 



iodide in 0-5000 grm. of salt weighed out. 



The sulphuric acid used in the determinations was absolutely 

 free from nitrous fumes, as an exceedingly slight trace will 

 greatly increase the dilution at which chlorine is liberated. 



Solutions of iodine and sodium thiosulphate of approximately 

 N/10 strength were carefully standardized, the iodine against 

 N/10 arsenite and the thiosulphate against the iodine with the 

 use of starch as indicator. The halogen salts were kept over 

 sulphuric acid in a desiccator and were weighed directly for 

 each determination. 



The form of apparatus used for the distillation and absorption 

 of liberated bromine in the earlier work, and shown in the accom- 

 panying figure (fig. 1), was again used in the iodine and bromine 

 determination, the smaller Voit flask being replaced therein, by 

 an ether wash-bottle having the larger capacity of 200 cmS . All 

 joints in the apparatus were of glass. The ether wash-bottle 

 which served as the distillation flask was graduated with etched 

 lines at 10 cm3 intervals. A thick platinum wire so bent as to rest 

 upon the bottom of the flask with the two ends upright was 

 used as an aid in indicating the final volumes of 70 cm3 and 

 18 cm3 . The Drechsel bottle, which served as the receiver of the 



