170 [iodide of iron by double decomposition. 
ART. XXXII— IODIDE OF IRON OBTAINED BY DOUBLE 
DECOMPOSITION. 
Extracted from a Memoir on Iodide of Iron, by M. Ch. Calloud. 
By reducing iodide of potassium and sulphate of the 
protoxide of iron into fine powder, and triturating the mix- 
ture of the two salts, I have obtained proto-iodide of iron : 
1 equiv. sulphate of the protoxide of iron 139.1 
1 " iodide of potassium 165.45 
The mixture of the two salts, well pulverized, is triturat- 
ed for a short time in an iron mortar ; the double decompo- 
sition which is effected by the aid of the water of crystalliza- 
tion of the sulphate of iron, is known to be complete 
when the saline mixture has become humid; it is then 
treated by alcohol 36° Baume, which dissolves only the 
proto-iodide of iron formed. 
When the reaction is entirely eifected, the sulphate of 
potassa is left in the condition of an insoluble salt, whence 
the following formula can be established : 
(FeO,SOs,7HO)+KI=KO,SOs + FeI + 7HO 
Analysis. — The alcoholic solution of proto-iodide of iron 
by double decomposition is lightly greenish, has a styptic 
ferruginous taste, but not at all bitter or acrid. Diluted 
with water, it is not precipitated by nitrate of baryta. Ex- 
posed to the air, it behaves in the same manner as solutions 
of the proto-salts of iron, to wit : it becomes colored yellow, 
afterwards brown, forms an ochreous deposit of sesquioxide, 
or basic salt, at the same time that the presence of free 
iodine becomes evident. 
Hydrate of potassa gives a precipitate of protoxide of 
iron, which being brought to the state of sesquioxide, cor- 
responds with the proportion of iodide of iron produced. 
Iodide of potassium, reconstituted from it, represents the 
quantity employed, except a slight loss. 
