G6 SIXTH REPOKT — 183G. 



On the Conducting Potvers of Iodine. By James Inglis, M.D. 



The author in this communication replies to objections which had 

 been raised rehxtive to the assertion contained in liis Prize Essay on 

 iodine, viz., that this substance is a conductor of electricity. In the 

 experiments which he instituted for the purpose he employed iodine 

 from the manufactorj' of Mr. Whitelaw of Glasgow, where no iron 

 vessel is ever employed, and in which in its veriest impurity no iron 

 can be detected. He exhibited a tube containing an aqueous solution of 

 ioduret of iron, a second containing an aqueous solution of the iodine to 

 be tested, and a third having in it a solution of the ferrocyanate of 

 potass. Now, on adding a portion of the last to the iron solution, im- 

 mediately theblueferrocyanate of iron is formed, but no such effect takes 

 place when added to the solution of iodine. Add, however, now a sin- 

 gle drop of the ioduret solution and instantly the blue precipitate falls. 



But supposing that a small portion of the ioduret was present, we 

 know that from its great affinity for water it could be removed by 

 washing. Being therefore Avashed, thoroughly dried with blotting 

 paper, and lastly sublimed three times, it is presumed the iodine used 

 was as pure as possible. 



Having put a portion of this into a tube with a platinum wire her- 

 metically sealed into one extremity, a second wire was introduced at 

 the other, till one end approached the former to within about the fourth 

 of an inch ; this extremity Avas now hermetically sealed ; so that the 

 arrangement consisted in a closed tube containing perfectly diy and 

 pure iodine, with two separate platinum wires communicating together 

 only through the medium of the iodine. A galvanic trough was now 

 charged, and one of the platinum wires attached to the positive pole, 

 whilst the other was placed in a glass of acidulated water ; on forming 

 the galvanic circle no effect was produced, nor was there any differ- 

 ence on reversing the poles. 



The iodine being now liquified by the flame of a spirit lamp, and 

 the tube attached to the negative pole, the platinum wire was placed as 

 before in water, and on completing the circle by a copper wire from the 

 positive pole, instantly bubbles of gas appeared, and were evolved at 

 the platinum wire, whilst none appeared at the copper, being positive. 



The order being reversed, evolution took place at both wires, proving 

 clearly that decomposition had been effected. Again, on placing the 

 wire on the tongue, and touching the other pole, a strong galvanic 

 sensation is instantly experienced. On remoA-ing the heat the power 

 of conducting gradually dies away, so that in seven minutes it is in- 

 capable of transmitting even sufficient to be felt by the tongue. There- 

 fore Dr. Inglis, when he stated in a note attached to Mr. Solly's paper 

 that iodine when cold and concrete still conducted, was in error, being 

 led to say so from recollection only. But his general statement that 

 iodine was a conductor is satisfactorily shown to be borne out by experi- 

 ment. 



