116 EEPOET— 1891. 



4. Note on Magnesium Iodide. 



By N. T. M. WiLSMOEE, B.Sc. 



The best way to prepare this substance in the anhydrous con- 

 dition is by the method described under experiment I. in the 

 preceding paper, using sufficient ethyl iodide to use up the 

 whole of the metal. The reaction goes best if the metal be 

 first strongly heated (preferably in hydrogen, though air will 

 do). It is then got as a fine amorphous powder, very suitable 

 for studying its behaviour with other bodies. Prepared in this 

 way, however, it always contains a little metallic magnesium, 

 even though considerable excess of ethyl iodide be employed ; 

 and also some organic matter, probably paraffines. An 

 analysis gave the following results : — 



99-90 100-00 



Magnesium iodide was also made by heating the metal in a 

 current of hydrogen and iodine vapour in a glass tube, and 

 also in hydriodic-acid gas ; but the action does not commence 

 till a dull-red heat is reached, and is then so violent that the 

 iodide is formed in a fused state, which solidifies to a hard 

 porcelain mass, very unsuitable for experimenting with. 



In hydrogen, magnesium iodide is stable at a red heat. In 

 air, at the ordinary temperature, it turns brown from separa- 

 tion of iodine, and deliquesces ; and at a full red heat it loses 

 the whole of its iodine, being converted into magnesium oxide. 

 When prepared by the ethyl-iodide method it acts on water 

 with considerable energy, which might easilj' be mistaken for 

 the action of an ethide, as was done by Hallwachs and 

 Schafarik ; but there is no gas given off, as would be the case 

 with an ethide. This was proved by wrapping up some in a 

 piece of paper, and immersing it under an inverted test-tube 

 full of water. The aqueous solution of the iodide prepared in 

 this way always has a peculiar smell, due probably to the 

 before-mentioned paraffines. Magnesium iodide also dissolves 

 in boiling anhydrous ether, separating out on cooling as 

 colourless crystals, which appear to have the composition 

 Mgl„ . 2(02115)20, though this requires further investigation. 



