DETECTION OF IODIDES IN THE BROMIDES. 121 
ART. XXIV.—SfMPLE PROCESS FOR DETECTING THE 
PRESENCE OF MINUTE QUANTITIES OF IODIDE IN 
THE BROMIDES OF THE ALKALIES. 
BY M. LASSAIGNE. 
The presence of the iodides of the alkalies in the bro- 
mides, which are now prepared by chemical manufacturers 
with bromine, obtained from the mother-waters of sea-salt 
works, is more frequent than may be supposed. This cir- 
cumstance arises, as is known to Chemists, from the diffi- 
culty of isolating bromine, which is liquid at ordinary tem- 
peratures, from small portions of iodine found in the state of 
bromide. 
Various samples of bromide of potassium, met with in 
commerce, have always afforded to M. Lassaigne a very 
small quantity of iodine; and it has been by means of the 
very delicate indication of the presence of free iodine which 
starch affords, that he has been able to make this observa- 
tion. 
On adding to a solution of the bromide of potassium to be 
examined, a few drops of a weak solution of chlorine, the 
liquor will be immediately colored yellow; if now a piece 
of while starched paper be introduced, it will be colored 
violet, or feeble indigo blue. This coloration depends upon 
the proportion of iodine set at liberty by the first addition 
of chlorine to the impure bromide. 
When a sufficient quantity of the solution of chlorine is 
added, to decompose the bromide of potassium, the starch- 
paper is not immediately colored; for, in this case, the 
iodine exists in the liquor in the state of bromide, which 
does not act on the starch; but these remarkable pheno- 
mena are presented, the paper being removed from the 
