322 
DETECTION OF IODIDE IN BROMIDE OF POTASSIUM. 
Officers for the session 1864-5. The result of the election was as follows :—President, 
Mr. Joseph Haigh ; Treasurer, Mr. J. Laud ; Secretary, Mr. E. Yewdall; Librarian, Mr. 
E. M. Atkinson ; Committee, Messrs. Jefferson, Eeynolds, Stead, B. Taylor, Thompson, 
and Ward ; Auditors, Messrs. Bilbrough and Eeinhardt. 
The thanks of the meeting were offered to the retiring officers. 
ORIGINAL AND EXTRACTED ARTICLES. 
THE APPLICATION OE THE STARCH TEST TOR DETECTING 
IODIDE IN BROMIDE OE POTASSIUM. 
BY MR. WILLIAM HUSIvISSON, JUN. 
Having been much engaged in the preparation of bromide of potassium, and 
having taken every precaution for ensuring a perfect salt, both as regards its 
purity and general characters, some weeks since my attention was directed to 
the fact that it contained iodide, or traces of iodine. 
In the 1 Chemical News ’ of Saturday last, the 19tli inst., Mr. F. Fewtrell 
states:—Recently it has been observed that bromide of potassium adminis¬ 
tered in large doses has been occasionally followed by symptoms of iodism, or 
the peculiar affections which are sometimes produced by excessive doses of iodine 
or iodide of potassium ; as no such effects followed the use of the pure bromide, 
the circumstance gave rise to a suspicion of the presence of iodide.” He fur¬ 
ther states,— u Having procured a sample which was labelled c bromide of potas¬ 
sium, French,’ which was well crystallized, the crystals being perhaps rather 
more opaque than those of the pure bromide, on a quantitative analysis being 
made it showed the presence of iodide of potassium to the amount of twenty 
per cent.* 
To the suspected solution of the bromide of potassium I had prepared, the 
following tests were applied :—A few drops of solution of chlorine were added, 
then a few drops of bisulphide of carbon. The bead that was formed remained 
colourless, or turned slightly yellow. Had the bromide contained more than 
traces of iodide, the bead would have collected the iodine developed by the 
chlorine and changed it to a rose colour of surpassing beauty, which, in the 
course of a few hours, would again change on the further collection of iodine to 
a rich violet colour, which would remain permanent. A little chlorine gas was 
then brought in contact with the solution, which failed to separate any iodine. 
On the addition of nitrate or chloride of palladium, a slight brown tint was 
communicated to the solution ; and after the lapse of some hours a slight brown 
precipitate separated.f 
The solution was then mixed with boiled starch, and a drop of solution of 
chlorine, or what is still better, a breath of chlorine gas passed over the surface, 
the blue iodide of starch was instantly developed. The solution of bromide 
was then mixed with boiled starch, and acidified with hydrochloric acid. On 
and addition of nitrite of potassa, the presence of iodine was manifest. Dr. 
Price has detected ^oouwoo P ar ^ iodine dissolved in water as iodide of potas¬ 
sium by this means. If much iodine is present, a dark blue colour will instantly 
* This would represent 15'3 per cent, of iodine. It should he observed that French 
bromide of potassium is sold at less than it would cost the English manufacturer to pro¬ 
duce jit. 
f Iodide of potassium occasions a black precipitate with nitrate or chloride of palladium. 
If chloride of palladium be added to a solution of one part of iodide of potassium in 400,000 
of water, it produces a brown tint. 
