[ *« ] 



LV. Extracts from a Prize Essay on Iodine. By James 

 Inglis, M.D.* 



A LL authors, from its discoverer down to the latest periods, 

 *^ have considered iodine as a non-conductor of electricity ; 

 but Mr. Kemp, of Edinburgh, two years ago satisfactorily 

 showed that this opinion was erroneous. I have found too that 

 when iodine in a state of perfect dryness was fused, it became a 

 conductor. All that is necessary is to fuse the iodine in a tube 

 closed at both extremities, and having a platinum wire herme- 

 tically sealed into each end, and connected to each other in- 

 ternally, only through the medium of the fused iodine. When 

 one of these is placed in attachment to the end of a galvanic 

 battery, and the other is dipped into water, the water is in- 

 stantly decomposed on the formation of the galvanic circlef. 

 We ought never to call any substance a non-conductor 

 until it be first tried in that state which brings its component 

 particles into close approximation ; for the best conductors in a 

 granulated state cease to transmit electricity, and even alumi- 

 num " in its fused state becomes a conductor of it J." 



Iodine imparts to water a decided brown tint; and M. Ampere 

 found that this colour entirely disappeared after the action of 

 solar light upon it. Gay-Lussac found that both hydriodic and 

 iodic acid existed in this decolorized water, so that the chlo- 

 rine solution reproduced the brown tint; but he does not con- 

 sider this action of iodine on water to be dependent on solar 

 light : he ascribes the deprivation of colour to the evaporation 

 of the iodine which was held in solution by the hydriodic acid 

 formed at the time when the iodine was added §. I found that 

 it was deprived of colour, whilst the bottle containing the so- 

 lution was tightly stoppered, so that the evaporation of iodine 

 could not be the cause of that change; but I found also that 

 a solution of iodine in water may be kept for any length of 

 time (the period I kept it was eighteen months), exposed to 

 the full action of the sun's rays, without an alteration of 

 colour. All that is requisite is to exclude the air ; for when, 

 instead of filling the bottle full of the solution, I only made 

 it half full, the other half being atmospheric air, then in a very 

 short time the colour was destroyed ; and this is not from the 



* Communicated by the Author. 



t [It is not quite clear from this statement whether the experiment was 

 made while the iodine retained the liquid form, or after it had assumed the 

 dense solid state by cooling. Perhaps Dr. Inglis will supply the required 

 information, as it may have some important bearings. — E. W. B.] 



\ Antony Tod Thomson's Therapeutics, vol. i. p. 139. 



§ Annates de Chimie, vol. xci. p. 155. Berzelius, Traiti de Chiin. 1829,, 

 p. 2i)8. 



Third Series. Vol. 7. No. 42. Dec. 1835. 3 L 



