POTASSII IODIDUM - IODIDE OF POTASSIUM, KI,=166.

Preparation

(1) By adding iodine to liquor potassae in slight excess, as indicated by a pale brown color of the solution. (2) The resulting mixture of iodide and iodate of potash is then heated with finely powdered charcoal, which deoxidizes the latter salt, so that iodide only remains: it is dissolved out and crystallized.

(1) 6KHO + 6I=5KI+KIO3 + 3H1O.

(2) KIO3+C3=KI+3CO.

Characters And Tests

Occurs in white crystals, usually cubical and opaque, but sometimes octahedral and transparent. When pure these are odorless, but they commonly have some scent of free iodine, and if this is present they are tinged more or less yellow. The taste is saline. It is very soluble in water and in six parts of rectified spirit. Nitrate of silver precipitates a pale yellow iodide of silver, insoluble in ammonia. If this liquid be then acidified with nitric acid, no precipitate should occur; if it does occur, chlorides are present. The most important adulteration - not, however, a very frequent one - is the iodate of potash, and this is detected by its insolubility in rectified spirit, and also by the blue color developed on adding prepared starch and a little acid, e.g., tartaric.

Sodii Iodidum - Ammonii Iodidum (Not Officinal)

The iodides of sodium and of ammonium are prepared in a similar manner to the last described, and have similar characters, and may be tested in the same way.

IODOFORMUM - IODOFORM, CHI3,=394 (NOT OFFICINAL).

Is a teriodide of formyl, and may be prepared by adding chlorinated lime to an alcoholic solution of iodine, heated to 104° F., till the liquid ceases to assume a red color. Confused crystalline masses of iodate of lime and iodoform precipitate on cooling; the latter is dissolved out by boiling alcohol, and deposited in small, pearly, yellow crystals of sweetish taste and penetrating, characteristic odor. It is insoluble in water, but soluble in boiling spirits (10 parts), ether (20 parts); also in chloroform, bisulphide of carbon, and oils; partially volatilized by heat; contains nine-tenths of its weight of iodine (Bouchardat).