Chemical elements
  Sulphur
    Isotopes
    Energy
    Extraction
    Refining
    Applications
    Allotropy
    Crystalline
    Amorphous Sulphur
    Colloidal Sulphur
    Physical Properties
    Chemical Properties
    Detection
    Estimation
    Compounds
      Hydrogen Sulphide
      Metal Polysulphides
      Hydrogen Polysulphides
      Hydrogen Pentasulphide
      Hydrogen Trisulphide
      Hydrogen Disulphide
      Sulphur Monofluoride
      Sulphur Tetrafluoride
      Sulphur Hexafluoride
      Sulphur Monochloride
      Sulphur Dichloride
      Sulphur Tetrachloride
      Sulphur Monobromide
      Thionyl Fluoride
      Sulphuryl Fluoride
      Fluorosulphonic Acid
      Thionyl Chloride
      Sulphuryl Chloride
      Sulphur Oxytetrachloride
      Pyrosulphuryl Chloride
      Chlorosulphonic Acid
      Thionyl Bromide
      Sodium Sulphoxylate
      Sulphur Dioxide
      Sulphurous Acid
      Sulphites
      Sulphur Trioxide
      Pyrosulphuric Acid
      Pyrosulphates
      Sulphuric Acid
      Persulphuric Anhydride
      Persulphuric Acid or Perdisulphuric Acid
      Perdisulphates
      Permonosulphuric Acid
      Amidopermonosulphuric Acid
      Thiosulphuric Acid
      Thiosulphates
      Polythionic Acids
      Dithionic Acid
      Trithionic Acid
      Trithionates
      Tetrathionic Acid
      Tetrathionates
      Pentathionic Acid
      Pentathionates
      Wackenroders Solution
      Hexathionic Acid
      Polythionic Acids
      Sulphur Sesquioxide
      Hydrosulphurous Acid
      Hydrosulphites
      Nitrogen Sulphide
      Nitrogen Persulphide
      Nitrogen Pentasulphide
      Sulphammonium
      Hexasulphamide
      Nitrogen Chlorosulphide
      Trithiazyl Chloride
      Thiotrithiazyl Chloride
      Dithiotetrathiazyl Chloride
      Nitrogen Bromosulphide
      Thiotrithiazyl Bromide
      Thiotrithiazyl Iodide
      Thiotrithiazyl Nitrate
      Thiotrithiazyl Hydrogen Sulphate
      Thiotrithiazyl Thiocyanate
      Thionylamide
      Sulphamide
      Imidodisulphamide
      Sulphimide
      Sulphonic Acids
      Amidosulphonic Acid
      Imidosulphonic Acid
      Nitrilosulphonic Acid
      Hydroxylamine-monosulphonic Acid
      Nitrososulphonic Acid
      Hydroxylamine-disulphonic Acid
      Hydroxylamine-isodisulphonic Acid
      Hydroxylamine-trisulphonic Acid
      Dihydroxylamidosulphonic Acid
      Sulphazinic Acid
      Sulphazotinic Acid
      Dehydrosulphazotinic Acid
      Nitrosulphonic Acid
      Nitrosulphonyl Chloride
      Nitrosulphonic Anhydride
      Nitrosulphuric Acid
      Nitrosodisulphonic Acid
      Sulphonitronic Acid
      Sulphates of Hydroxylamine
      Hydroxylamine Dithionate
      Hydrazine Dithionate
      Hydrazine Amidosulphonate
      Carbon Subsulphide
      Carbon Monosulphide
      Carbon Disulphide
      Thioformaldehyde
      Thiocarbonic Acid
      Ammonium thiocarbonate
      Thiolcarbonic Acid
      Xanthic Acid
      Perthiocarbonic Acid
      Sodium perthiocarbonate
      Carbonyl Sulphide
      Thiocarbonyl Chloride
      Thiocarbonyl Tetrachloride or
      Carbon Hexachlorosulphide
      Trichloromethyl Disulphide
      Thiocarbonyl Sulphochloride
      Carbon Bromosulphide
      Amino-derivatives of Thiocarbonic Acid
      Dithiocarbamic Acid
      Thiocarbamide
      Azidodithiocarbonic Acid
      Thiocyanogen
      Cyanogen Monosulphide
      Cyanogen Trisulphide
      Sulphur Thiocyanate
      Disulphur Dithiocyanate
      Thiocyanic Acid
      Thiocyanates
      Dithiocyanic Acid
      Trithiocyanuric Acid
      Perthiocyanic Acid
      Perthiocyanogen
      Sulphates

Perdisulphates






Preparation of Perdisulphates
Apparatus for Preparation of Perdisulphates.
A similar process to the electrolytic preparation of perdisulphuric acid is possible for the preparation of the perdisulphates. The corresponding alkali hydrogen sulphate or a mixture of the normal sulphate and sulphuric acid in cold aqueous solution is electrolysed in a cell so arranged that the anode and cathode are separated by a porous diaphragm, or at least arranged so that the cathode gases shall not pass near the anode; a convenient experimental apparatus is represented in the diagram (fig.). The yield of alkali perdisulphate is increased by the presence of nickel sulphate, aluminium sulphate, alkali fluoride, potassium thiocyanate or potassium ferricyanide in the electrolyte, and also by the application of a high current density at the anode, which should therefore be as small as is convenient. A platinum anode is commonly used, and this should be of smooth metal; electrodes of aluminium and tin have also been recommended.

As in the electrolytic formation of perdisulphuric acid, the first anodic product is the discharged HSO4' ion, which by coupling then gives rise to perdisulphuric acid. If the metal perdisulphate is less soluble than the acid sulphate, it crystallises from the solution; this is the case in the electrolysis of a concentrated solution of potassium or ammonium hydrogen sulphate,8 the changes in the case of the latter salt being as follows:

HSO4' + + = HSO4,
2HSO4 = H2S2O8,
H2S2O8 + (NH4)HSO4 = (NH4)2S2O8 + 2H2SO4.

Ammonium perdisulphate has also been prepared by passing fluorine into a cold saturated aqueous solution of ammonium hydrogen sulphate; ozonised oxygen escapes as oxidation proceeds and crystals of the persulphate slowly separate.

The perdisulphates of the alkaline earth metals may be prepared by grinding together, with a little water, molecular proportions of the metal oxide and ammonium perdisulphate, and drying the mixture in a vacuum. The resulting mass is carefully powdered and the metal perdisulphate extracted by solution in absolute alcohol, from which it may be obtained by the addition of absolute ether, or by evaporation in a vacuum.
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