Chemical elements
    Physical Properties
    Chemical Properties
      Carbon Tetrafluoride
      Carbon Tetrachloride
      Carbon Tetrabromide
      Carbon Tetraiodide
      Carbon Oxychloride
      Carbonyl Chloride
      Carbon Oxybromide
      Carbonyl Bromide
      Carbon Suboxide
      Carbon Monoxide
      Carbon Dioxide
      Percarbonic Acid
      Carbamic Acid
      Carbon Disulphide
      Carbonyl Sulphide
      Carbon Oxysulphide
      Thiocarbonyl Chloride
      Thiocarbonic Acid
      Thiocarbamic acid
      Carbon Monosulphide
      Carbon Subsulphide
      Carbon Sulphidoselenide
      Carbon Sulphidotelluride
      Carbon Nitrides
      Hydrocyanic Acid
      Prussic Acid
      Cyanogen Chloride
      Cyanogen Bromide
      Cyanogen Iodide
      Polymerised Cyanogen Halides
      Cyanic Acid
      Cyanuric Acid
      Fulminic Acid
      Thiocyanic Acid
      Sulphocyanic Acid
      Isoperthiocyanic Acid
      Cyanogen Sulphide
      Thiocyanic Anhydride
    Amorphous Carbon

Cyanogen Iodide, CNI

This compound is formed by the action of iodine on mercuric cyanide; if the iodine is dissolved in anhydrous ether the cyanogen iodide goes into solution in the ether, and remains behind after the evaporation of the latter.

Iodide of cyanogen crystallises in long white needles which melt at 146-5° C. and easily sublime, giving a vapour whose density corresponds to the formula CNI, has an unpleasant smell like that of the bromide, and is very poisonous. This compound often occurs as an impurity in commercial iodine. Its heat of formation from its elements is -23,100 calories, and from (CN)2 and I2 + 17,900 calories. It is easily soluble in alcohol and ether, sparingly so in water. This compound is unchanged in aqueous solution by hydrochloric or sulphuric acid, but reacts with hydriodic acid thus:

CNI + HI = HCN + I2.

The reaction between cyanogen iodide and a soluble iodide in aqueous solution is brought about by the presence of hydrogen ions. It has therefore been proposed to use it as a method of acidimetry.

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