Chemical elements
    Physical Properties
    Chemical Properties
      Hydrogen Selenide
      Selenium Fluorides
      Selenium Monochloride
      Selenium Tetrachloride
      Selenium Monobromide
      Selenium Tetrabromide
      Selenium Chlorobromides
      Selenium Oxyfluoride
      Selenium Oxychloride
      Sulphur Selenium Oxytetrachloride
      Selenium Oxybromide
      Chloroselenic Acid
      Selenium Dioxide
      Selenious Acid
      Selenium Trioxide
      Selenic Acid
      Perselenic Acid
      Selenium Sulphoxide
      Selenotrithionic Acid
      Diselenotrithionic Acid
      Selenopentathionic Acid
      Selenium Nitride
      Nitrosylselenic Acid
      Phosphorus Subselenide
      Phosphorus Monoselenide
      Tetraphosphorus Triselenide
      Phosphorus Triselenide
      Phosphorus Pentaselenide
      Phosphorus Chloroselenide
      Selenophosphates and Oxyselenophosphates
      Carbon Diselenide
      Carbon Subselenides
      Carbon Oxyselenide
      Carbon Sulphidoselenide
      Cyanogen Monoselenide
      Cyanogen Diselenide or Selenocyanogen
      Cyanogen Triselenide
      Selenocyanic Acid
      Ammonium Selenocyanate
      Caesium Triselenocyanate
      Copper Selenocyanate
      Lead Selenocyanate
      Magnesium Selenocyanate
      Mercurous Selenocyanate
      Mercuric Selenocyanate
      Potassium Selenocyanate
      Silver Selenocyanate
      Sodium Selenocyanate
      Zinc Selenocyanate
      Silicon Selenide
    Detection and Estimation

Selenium Sulphoxide, SeSO3

Selenium Sulphoxide or Sulphur - Selenium Sesquioxide, SeSO3, has already been mentioned in connection with the solubility of selenium in sulphuric acid as the probable cause of the green colour produced. It is also obtainable, similarly to sulphur sesquioxide, from fluid sulphur trioxide by the addition of powdered amorphous selenium, the sulphoxide being insoluble in the sulphur trioxide, so that the latter can be decanted off:

Se + H2SO4 = SeSO3 + H2O;
Se + SO3 = SeSO3.

It is described as a green liquid, solidifying to a green solid, which easily passes into a yellow modification. It is slightly more stable than sulphur sesquioxide, but decomposes on gentle heating. The compound SeO2.SO3 has already been mentioned.

Selenosulphuric Acid or Thioselenic Acid, H2SSeO3. - Salts of this acid are obtained when finely divided selenium is dissolved by warming with an aqueous solution of an alkali sulphite, potassium sulphite being the most satisfactory:

K2SO3 + Se = K2SSeO3.

The selenosulphates are very unstable and their solutions undergo partial decomposition with separation of red selenium even on mere dilution with water. The addition of acids immediately effects decomposition with formation of selenium, selenosulphuric acid itself being incapable of free existence:

K2SSeO3 + 2HCl = 2KCl + H2SO3 + Se.

The addition of iodine also brings about immediate decomposition with liberation of selenium.

The evidence supplied by the method of formation and the occurrence of isomerism as to analogous structures for the thiosulphates and selenosulphates, is amplified by the chemical behaviour of the potassium alkyl selenosulphates, obtained by treatment of potassium selenosulphates with alkyl halides. These, on electrolytic reduction and also on oxidation with hydrogen peroxide, yield the corresponding diselenides. The structure of the selenosulphates therefore involves a selenium atom directly attached to potassium, thus

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