Iodine. - A non-metallic element obtained from the ashes of sea-weeds and from mineral iodides and iodates.

Characters. - Heavy, bluish-black, rhombic plates of a peculiar odour and metallic lustre, which, when heated, yield a beautiful violet-coloured vapour.

Preparation. - Vide p. 548.

Solubility. - It is very sparingly soluble in water, but freely dissolved by alcohol, by ether, and by a solution of iodide of potassium.

Reaction. - The aqueous solution strikes a deep blue colour with starch.

Impurities. - Moisture, metallic impurities fraudulently added, cyanide of iodine (the nitrogen in this is yielded by marine animals amongst the seaweed), chloride of iodine, chlorine and bromine.

Tests. - .It should not adhere to the sides of the bottle, and its solution in chloroform should be clear and limpid (absence of moisture). It sublimes as a purple vapour without leaving any residue (absence of fixed impurities), and the portion that first comes over does not include any slender colourless prisms emitting a pungent odour (absence of cyanide of iodine); 12.7 grains dissolved in an ounce of water containing fifteen grains of iodide of potassium require for complete discoloration 1,000 grain-measures of the volumetric solution of hyposulphite of sodium.

Preparations, b.p.

Arsenii Iodidum.

Emplastrum Plumbi Iodidi.

Hydrargyri Iodidum Eubrum.

Iodoformum.

Linimentum Iodi (p. 516).

Linimentum Potassii Iodidi cum Sapone (p. 516). Liquor Iodi, aqueous solution (1 in

20). Pilula Ferri Iodidi (p. 522). Plumbi Iodidum. Potassii Iodidum. Sodii Iodidum.

Sulphuris Iodidum.

Syrupus Ferri Iodidi.

Tinctura Iodi, alcoholic solution (1 in 40). Unguentum Hydrargyri Iodidi Rubri. * „ Iodi (1 in 31).

„ Plumbi Iodidi.

„ Potassii Iodidi.

,, Sulphuris Iodidi.

*Vapor Iodi (Tincture of Iodine, 1 fl. dr. mixed with 1 fl. oz. of water, gently warmed, and the vapour inhaled).

U.S.P

Ammonii Iodidum. Argenti Iodidum. Arsenici Iodidum. *Liquor Iodi Compositus (5 in 100). Plumbi Iodidum. Potassii Iodidum. Sodii Iodidum.

Sulphuris Iodidum. Tinctura Iodi (8 in 100). *Unguentum Iodi (4 in 100).

„ Plumbi Iodidi.

„ Potassii Iodi.

Zinci Iodidum.

The preparations marked with * in the preceding list contain iodine in a free state dissolved by the aid of iodide of potassium (p. 556). Tinctura Iodi U.S.P. contains free iodine dissolved in alcohol. The others contain it in a state of combination.

U.S.P. Liquor Iodi Compositus. Iodine 5, iodide of potassium 10, distilled water 85. This solution differs from Liquor Iodi P.B., only in containing 10 per cent. of iodide of potassium, while the B.P. preparation contains 7 1/2 per cent.