290 
ON IODIDE OP POTASSIUM. 
tained in the bason, and mix by agitation, taking care to 
remove the hand occasionally from the mouth of the flask, 
to allow of the escape of carbonic acid, which is slowly 
given off; in doing so, the operator must be careful to give 
vent to the pent-up gas on the side of the flask farthest 
from his person, otherwise he will run the risk of having 
his clothes disfigured with red stains from the ferruginous 
liquid. 
If the mixture be made at a somewhat higher heat, the 
escape of gas is so rapid, that there is great danger of the 
liquid boiling over, and thus leading to considerable loss ; 
on the other hand, if the solutions be mixed at a lower tem- 
perature, the precipitate is very slow of subsiding, and this 
interferes with and retards the process. 
We now fill up the flask to the commencement of the 
neck with distilled water recently boiled, agitate, and set 
aside to allow the precipitate to settle; our reason for filling 
up the flask to its narrowest part is, that as small an extent 
of surface as possible may be presented to the decomposing 
action of the air. 
We have now in the flask a solution of iodide of potas- 
sium, with an excess of iodide of iron, together with a 
bulky white precipitate of protocarbonate of iron. 
To neutralize the excess of iodide of iron, either of two 
methods may be adopted: We may at once proceed to neu- 
tralize the excess by adding, gradually, the solution of the 
carbonate from the test glass, agitating after each addition, 
until the liquid restore the blue color to litmus reddened 
with a single drop of muriatic acid to about six ounces of 
water. This can be easily managed by dipping the point 
of a glass rod into the mixture in the flask, and then apply- 
ing it to one of a number of small slips of the paper placed 
by the side of the operator. We give the preference to the 
other method. 
After the precipitate has sufficiently settled to give a clear 
liquid, we pour in a little of the solution of the alkaline car- 
