ON IODIDE OP POTASSIUM. 
293 
suits more from the action of the iron than the expulsion of 
free iodine by the heat. At any rate, however rapidly heat 
may be applied, there is very little escape of iodine, and 
we never found that we obtained a less quantity of iodide 
of potassium when a quick heat was used than when it was 
more gentle. 
Having now prepared a strong solution of iodide of iron, 
which is done in a few minutes, we allow it to settle a little; 
then pour it into a phial from the sediment without filtration; 
about an ounce of water may then be poured into the flask, 
and the sediment washed with it, and, after subsidence, 
poured into the concentrated solution of iodide of potassium. 
We now continue adding gradually more from the phial, 
till the liquid ceases to restore the blue color to reddened 
litmus. 
After heating to aggregate the precipitate, we filter the 
liquid, washing the precipitate properly; for this purpose 
we use a double filter, the liquid being so dense that a single 
one would inevitably give way under its weight: unite the 
liquids and evaporate to dryness, and fuse the dry salt in an 
iron pot provided with a cover; the fusion may be easily 
accomplished with a brisk open fire, and care must betaken 
not to continue the heat a single instant after complete fusion 
has been effected. 
Wilhout the application of a heat sufficient to fuse the 
iodide, we cannot, without great difficulty, obtain it free of 
color, probably arising from excess of iodine, and possibly 
organic matter; but in this way they are both completely 
removed. 
By dissolving out the iodide and filtration we get a per- 
fectly colorless solution, and by successive concentration 
and cooling, we obtained a perfectly pure and colorless 
iodide nearly to the very last. 
Whenever the crystals begin to show the presence of im- 
purities, which can be easily known by the form and ap- 
pearance they present, or their partial solubility in alcohol, 
26* 
