NEW METHOD OF PREPARING IODIDE OP POTASSIUM. 301 
ART. LXIII.-ON A NEW METHOD OF PREPARING IODIDE 
OF POTASSIUM. By R. Phillips, Jun. 
In examining six samples of iodide of potassium, pro- 
cured at different chemists, the author found that No. 1 
was strongly alkaline, and contained water, iodate of potash 
and chloride of potassium or sodium ; No. 2 resembled No. 
1, except that it contained a larger quantity of iodate ; No. 
3 was slightly alkaline, contained no water, but a trace of 
an iodate and chloride ; No. 4 resembled No. 1 ; No. 5 was 
almost pure, containing only a trace of iodate and water ; 
No. 6 resembled No. 1. The author proposes the decom- 
position of the iodide with nitrate of silver, washing the 
precipitate with distilled water, and then digestion in strong 
solution of ammonia, as a readier and better process for 
detecting the adulteration with a chloride than the method 
in general use. If the filtered ammoniacal solution, acidified 
with nitric acid, give a white precipitate, it is chloride of 
silver, and denotes the presence of a chloride of potassium 
and sodium. In testing for iodate of potash, the solution of 
the iodide in cold distilled water is to be acidulated with tar- 
taric acid, and a solution of starch added ; if the mixture 
does not become of a dark color, no iodate is present. 
The author's process consists in decomposing the iodate 
of potash formed by the action of iodine on potash by 
protoxide of iron. The usual method, viz., fusion of the 
iodide so as to decompose the iodate, is objectionable, because 
a heat which is sufficient to decompose the iodate renders 
the iodide volatile. The protoxide of iron is easily prepar- 
ed by precipitation with the alkalies from the protosulphate 
of iron. The precipitate must be washed by decantation, 
until chloride of barium causes no precipitate in the water. 
Peroxide of iron being a sesquioxide, it is necessary, in 
vol. x. — no. iv. 27 
