THE 



LONDON AND EDINBURGH 



PHILOSOPHICAL MAGAZINE 



AND 



JOURNAL OF SCIENCE. 



[THIRD SERIES.] 



JULY 184-0. 



I. On the Iodide of a new Carbo-hydrogen. By JAMES 

 F. W. JOHNSTON, F.R.S.* 



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 constitu- 

 ting 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, con- 

 sisting of a mixture of Faraday's iodide of carbo-hydrogen 

 (H 2 C 2 I)f and of iodide of formyle (iodoform H C 2 I 3 ). 



The solid product being exposed to the air loses its unctu- 

 osity. If broken up and examined by the microscope it is 

 seen to consist of a congeries of colourless prisms (H 2 C 2 I) 

 mixed with another substance, which is amorphous, and of a 

 dark green almost black colour. Alcohol separates the for- 

 mer, 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 

 formyle and of carbo-hydrogen is easily understood. Coal 

 gas contains probably more than two equiatomic compounds 

 of carbon and hydrogen ; at least two, C H 2 and C 2 H 2 , the 



* Communicated by the Author. 



[f Mr. Faraday's account of this substance will be found in Phil. Mag. 

 First Series, vol. lix. p. 352. EDIT.] 



Phil Mag, S, 3, Vol. 17, No, 107, My 1840. B 



