Testing Procedure (Method of analysis) for Ferric salts, Ferrous Salts and Iodides

Ferric salts

A. Dissolve a quantity of the substance under examination containing about 10 mg of iron in 1 ml of water or use 1 ml of the prescribed solution. Add 1 ml of potassium ferrocyanide solution; an intense blue precipitate, insoluble in dilute hydrochloric acid, is produced.

B. To 3 ml of the solution containing about 0.1 mg of iron or to 3 ml of the prescribed solution add 1 ml of 2 M hydrochloric acid and 1 ml of ammonium thiocyanate solution; the solution becomes blood-red in color. Take two portions, each of] ml, of the mixture. To one portion add 5 ml of ether, shake and allow to stand; the ether layer is pink. To the other portion add 3 ml of 0.2 M mercuric chloride; the red color disappears.

C. To 2 ml of the solution containing about 0.1 mg of iron or to 3 ml of the prescribed solution add acetic acid until the solution is strongly acidic. Add 2 ml of a 0.2 percent w/v solution of 8-hydroxy-7-iodoquinoline-5-sulphonic acid; a stable green color is produced.

Ferrous Salts

A. Dissolve a quantity of the substance under examination containing about 10 mg of iron in 2 ml of water or use 2 ml of the prescribed solution. Add 2 ml of dilute sulphuric acid and 1 ml of a 0.1 percent w/v solution of 1,10-phenanthroline; an intense red color which is discharged by addition of a slight excess of 0.1 M ceric ammonium sulfate is produced.

B. To 1 ml of a solution containing not less than 1mg of iron or to 1 ml of the prescribed solution add 1 ml of potassium ferricyanide solution; a dark blue precipitate is formed that is insoluble in dilute hydrochloric acid and is decomposed by sodium hydroxide solution.

C. To 1 ml of a solution containing not less than 1mg of iron or to 1 ml of the prescribed solution add 1 ml of potassium ferrocyanide solution; a white precipitate is formed which rapidly becomes blue and is insoluble in dilute hydrochloric acid.

Iodides

A. Dissolve a quantity of the substance under examination containing about 4 mg of iodide ion in 2 ml of water or use 2 ml of the prescribed solution. Acidify with dilute nitric acid and add 0.5 ml of silver nitrate solution. Shake and allow to stand; a curdy, pale yellow precipitate is formed. Centrifuge and wash the precipitate rapidly with three quantities, each of 1 ml, of water, in subdued light. Suspend the precipitate in 2 ml of water and add 1.5 ml of 10 M ammonia; the precipitate does not dissolve.

B. To 0.2 ml of solution of the substance under examination containing about 5 mg of iodide ion per ml or to 0.2 ml of the prescribed solution add 0.5 ml of 1 M sulphuric acid, 0.15 ml of potassium dichromate solution, 2 ml of water and 2 ml of chloroform shake for few seconds and allow to stand; the chloroform layer is violet or violet-red.

C. To I ml of a solution of the substance under examination containing about 5 mg of iodide ion add 0.5 ml of mercuric chloride solution; a dark red precipitate is formed which is slightly soluble in an excess of this reagent and very soluble in an excess of potassium iodide solution.