Excerpt from The London, Edinburgh and Dublin Philosophical Magazine and Journal of Science, Vol. 17: New and United Series of the Philosophical Magazine, Annals of Philosophy, and Journal of Science; July December, 1840
If coal gas be made to pass slowly and for a length of time over pure iodine, the latter substance moistens, and is partly changed into a dark-brown liquid, which effervesces with alkaline carbonates, showing the presence of hydriodic acid. After some hours, colourless prismatic crystals shoot out from the iodine, and clothe the interior of the vessel, and ultimately the whole is changed into a mixture of different compounds forming an olive-coloured substance, partly coating thickly the sides of the vessel, and partly constituting an unctuous mass, with the dark fluid at the bottom.
The liquid contains free iodine and hydriodic acid. When washed out from the solid portion by alcohol and neutralized by caustic potash, the solution gives a yellow precipitate, consisting of a mixture of Faraday's iodide of carbo-hydrogen (H4 Cj I)f and of iodide of formyle (iodoform H C„ I3).
The solid product being exposed to the air loses its unctuosity. If broken up and examined by the microscope it is seen to consist of a congeries of colourless prisms (Ha Ca I) mixed with another substance, which is amorphous, and of a dark green almost black colour. Alcohol separates the former, or if the mixture be exposed to the air they volatilize, leaving the dark green substance nearly pure.
The production of the hydriodic acid and of the iodides of formyl and of carbo-hydrogen is easily understood.
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