Chemical elements
    Amorphous Sulphur
    Colloidal Sulphur
    Physical Properties
    Chemical Properties
      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
      Sulphur Trioxide
      Pyrosulphuric Acid
      Sulphuric Acid
      Persulphuric Anhydride
      Persulphuric Acid or Perdisulphuric Acid
      Permonosulphuric Acid
      Amidopermonosulphuric Acid
      Thiosulphuric Acid
      Polythionic Acids
      Dithionic Acid
      Trithionic Acid
      Tetrathionic Acid
      Pentathionic Acid
      Wackenroders Solution
      Hexathionic Acid
      Polythionic Acids
      Sulphur Sesquioxide
      Hydrosulphurous Acid
      Nitrogen Sulphide
      Nitrogen Persulphide
      Nitrogen Pentasulphide
      Nitrogen Chlorosulphide
      Trithiazyl Chloride
      Thiotrithiazyl Chloride
      Dithiotetrathiazyl Chloride
      Nitrogen Bromosulphide
      Thiotrithiazyl Bromide
      Thiotrithiazyl Iodide
      Thiotrithiazyl Nitrate
      Thiotrithiazyl Hydrogen Sulphate
      Thiotrithiazyl Thiocyanate
      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
      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
      Azidodithiocarbonic Acid
      Cyanogen Monosulphide
      Cyanogen Trisulphide
      Sulphur Thiocyanate
      Disulphur Dithiocyanate
      Thiocyanic Acid
      Dithiocyanic Acid
      Trithiocyanuric Acid
      Perthiocyanic Acid


The Pentathionates are salts that are unstable, and even those of the alkali metals are so difficult to prepare as to arouse a suggestion that the acid H2S5O6 had no real existence and that the so-called pentathionic acid was a colloidal solution of sulphur in aqueous tetrathionic acid. The definite existence of the acid was finally proved by the isolation of solid pentathionate by the cautious addition of a solution of hydroxide of barium or potassium to excess of the acid solution, when the tetrathionate crystallised first, followed by a deposit of pentathionate. In order to avoid further the harmful action of alkali on the free acid, Debus used the acetates of the metals in place of the hydroxides and recrystallised the pentathionate from water containing a little sulphuric acid. As potassium pentathionate is less dense than potassium tetrathionate, whilst a mixture of bromoform and xylene of specific gravity 2.2 has an intermediate density, it has been found possible to separate the potassium salts by addition of this liquid mixture, when the tetrathionate sinks and the pentathionate rises to the surface.

The pentathionates are not stable, decomposing spontaneously alone or in aqueous solution with gradual formation of tetrathionate, trithionate and sulphur, the change being retarded by the addition of a little hydrochloric or sulphuric acid. When heated in the dry condition they yield sulphate, sulphur and sulphur dioxide:

2K2S6O6 = 2K2SO4 + 2SO2 + 6S.

Hot alkaline solutions cause the pentathionates to undergo rapid conversion into thiosulphate, whilst with cold solutions some free sulphur is deposited, a corresponding amount of sulphite being produced, together with the thiosulphate:

2K2S5O6 + 6KOH = 5K2S2O3 + 3H2O.

Sodium carbonate causes deposition of sulphur and formation of tetrathionate:

K2S5O6K2S4O6 + S,

but the reaction is not quantitative as stated by Raschig, and also proceeds beyond this stage.

Sulphites give tetra- and tri-thionates and thiosulphate,

S5O6' + SO3S4O6' + S2O3',

the decomposition of the tetrathionate proceeding as already described. The reaction with bisulphites is similar, tetrathionate first being produced.

The action of hydrogen sulphide and of sulphur dioxide has already received mention under the description of the acid.

Potassium amalgam reduces an aqueous pentathionate solution to tetrathionate and thiosulphate. Metallic copper and silver are blackened by pentathionate solutions.

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