Manual of practical pharmaceutical chemistry / by George Robertson.

  • Robertson, George
Date:
[1889]
Catalogue details

Licence: Public Domain Mark

Credit: Manual of practical pharmaceutical chemistry / by George Robertson. Source: Wellcome Collection.

    58/134
    Mix the nitric acid with the remainder of the water (15 minims) and to the acid thus diluted, after making warm, add the solution of sulphate of iron. Now concentrate these mixed solutions by boiling until, by the sudden disengagement of ruddy vapours, the liquid ceases to be black and assumes a red colour. A drop of the solution is now to be tested with ferricyanide of potassium. If a blue precipitate forms, it denotes that the whole of the sulphate has not been converted into persulphate of iron. In this case add a few drops more nitric acid, and boil again until no further blue precipitate is formed. When cold, make the quantity up to 60 minims, if necessary, by the addition of distilled water. Notes on the Process:— 1. _ This solution should give a blue precipitate with potassium ferrocyanide, but not with potassium ferricyanide. 2. The black colour noticed in the process is due to a compound of sulphate of iron with nitric oxide g-as (zFeSOi + NO). 3. The chemical changes which take place in the preparation of liquor ferri persulphatis are expressed by the following equation:— 6FeS04 + 3H0SO4 + 2HNO3 = 3(Feo3S04) + 2NO + 4H2O. Ferrous Sulphuric Nitric Ferric Nitric ™ Sulphate. Acid. Acid. Sulphate. Oxide Gas. Water. 4. The sudden disengagement of ruddy vapours is due to the decomposition by greater heat of the black compound 2FeS04 + NO mentioned above. The nitric oxide gas (which is colourless), as it escapes unites with the oxygen of the air, and ruddy vapours of nitric peroxide gas are formed. 5. The object of adding sulphuric acid in the process is to prevent the formation of ferric nitrate. If sufficient sulphuric acid is not present, some ferric nitrate is formed, as seen by the following equation :— 6FeS04 + 8HNO3 = 2(Fe23S04) + Feo6N03 + 2NO + Sulphate Nitric Ferric Ferric Nitric o£ Iron. Acid. Sulphate. Nitrate. Oxide Gas. 4H3O. Water. 6. Diluted with ten volumes of water it should yield a white precipitate with chloride of barium (showing it to be a sulphate). When solutions of Ferric salts are mixed with solution of iodide of potassium, iodine is liberated. It is important that no prescriptions should contain remedies which destroy each other’s effect, either chemically or therapeutically; hence, ferric salts are imcompatible with iodide of potassium. y. The specific gravity should be 1.44 b a fluid drachm should yield 11.44 grains of ferric oxide.