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


Trithionates are salts of the general type X2S3O6, where X represents the equivalent weight of a metal; the alkali salts are the best known.

When heated alone the salts decompose with liberation of sulphur and sulphur dioxide:

K2S3O6 = K2SO4 + SO2 + S.

In aqueous solution alkali trithionates gradually undergo decomposition with formation of sulphate, hydrogen sulphite and tetrathionate. The course of the main reaction may be expressed ionically as follows:

(a) S3O6' + H2O = S2O3' + SO4' + 2H,
(b) S3O6' + S2O3' + H = S4O6' + SO3H'.

A trace of pentathionate is also found in the solution after the lapse of several days, probably formed according to

5S2O3' + 6H = 2S5O6' + 3H2O.

The decomposition is accelerated by the presence of acid, and sulphur is deposited:

(c) S2O3' + H = HSO3' + S.

In the presence of alkali decomposition is fairly rapid, sulphite and thiosulphate being the chief products:

2S3O6' + 6OH' = S2O3' + 4SO3'.

Thiosulphate is the sole product on treatment with an alkali sulphide:

K2S3O6 + Na2S = K2S2O3 + Na2S2O3.

The decomposition of trithionates in aqueous solution is only slightly influenced by the addition of sulphites or thiosulphates, although the latter catalytically accelerate the decomposition of tetra- or penta- thionates under similar conditions.

In the presence of hydrogen sulphide the reaction is extremely slow, and is retarded by the presence of acid:

S3O6' + H2S = 2S2O3' + H,
S2O3' + 2H2S + 2H = 3H2O + 4S.

On adding potassium trithionate to a cold solution of copper acetate and keeping for several days in the dark, transparent yellow monoclinic prisms separate. These have the composition K2S2O3.Cu2S2O3.2H2O, i.e. potassium cuprous thiosulphate. They are unstable in air or on boiling with water, cupric sulphide being formed. This reaction demonstrates the formation of thiosulphate during the hydrolysis of trithionate solutions.

The trithionates may be quantitatively precipitated by boiling for one hour with a mixture of copper sulphate and barium chloride solutions containing free hydrochloric acid:

S3O6' + 8Cu•• + 6H2O = 3SO4' + 8Cu + 12H.

Tetrathionates and thiosulphates interfere, but not penta- or hexa- thionates.

The salts derived from metals other than the alkali metals are relatively little known; all are stated to be easily soluble in water with the exception of the mercurous, mercuric and silver salts, which are sparingly soluble. In describing the properties of the acid mention has already been made of the precipitation reactions of the salts with silver nitrate and other salts, and of the behaviour of the salts towards the alkali hydroxides and sulphides.

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