218 ADULTERATION OF IODIDE OF POTASSIUM. 
copper, if we add an excess of sulphurous acid, which, act- 
ing in concert with the iodine, reduces the binoxide of cop- 
per to the state of protoxide, by itself passing into the state 
of sulphuric acid. 
As the same reaction does not take place in the case of 
the chlorides, this method has been applied to the discovery 
of chloride of potassium in the iodide; it remained to be 
seen whether it could also be employed for the detection of 
bromide in the same salt, I have satisfied myself by accu- 
rate experiment that it is equally correct as in the last case. 
The operation is performed in the following manner : — 
We dissolve the suspected iodide in a sufficient quantity of 
cold distilled water, we add an excess of sulphate of copper 
in solution, we then saturate the mixture with sulphurous 
acid ; as soon as the latter is in excess, the whole of the 
iodine is precipitated in the state of protoiodide of copper : 
while the bromide remains undecomposed, we separate the 
iodide of copper by filtration, and it may be weighed after 
being washed and dried. The water arising from the wash- 
ing is to be added to the filtered liquid, we add a fresh 
quantity of sulphate of copper and sulphurous acid and boil 
the mixture ; the whole of the bromide is then decomposed 
in its turn, and the bromine precipitated in the state of 
proto-bromide of copper, the quantity of which can be de- 
termined as in the first instance. 
If we should be content with the determination of the 
presence of bromine in the compound, it is sufficient, after 
having separated the iodide of copper by filtration, to place 
the liquid in a tube, pour upon it a little ether and chlora- 
ted water, then shake it, and, if left at rest, the ether will 
rise to the surface, bringing with it the whole of the bio- 
mine, which tinges it of a reddish-yellow colour. 
This method, by its simplicity and accuracy, is prefera- 
ble to that which consists in converting the mixture into 
iodide and bromide of silver, which are afterwards separa- 
ted by ammonia ; for the latter process almost always gives 
incorrect results. — Chemist, from Journ. de Pharm. 
