Dr. Inglis 071 the Electrical Conducting Power of Iodine. 45 V 



to the solution of iodine ; it remains the same as before admix- 

 ture. Add, however, but a single drop of the sohition of the 

 ioduret of iron and the blue colour instantly appears. But sup- 

 posing that a small portion of the ioduret by some chance 

 happened to be present, we know that from its great affinity 

 for water it could be removed by washing; I therefore washed 

 several times, and thoroughly dried, the iodine with blotting- 

 paper; and lastly, thrice sublimed it; so that now I presume 

 it is as pure as possible. 



Of this iodine thus prepared, I put a portion into a tube 

 with a platinum wire hermetically sealed into one extremity; 

 and introducing a second wire at the other till one end ap- 

 proached the former to within about the fourth of an inch, 

 I hermetically sealed this extremity also : so that we have 

 here a closed tube containing dry pure iodine, with two se- 

 parate platinum wires communicating together only through 

 the medium of the iodine. 



Thi-ee galvanic troughs, containing each 30 pairs of plates, 

 were charged, (but 20 pairs, or fewer, as in the trough now 

 to be used, are sufficient,) and one of the platinum wires fixed 

 to the positive pole, whilst the other was ))laced in a glass of 

 acidulated water. On forming the galvanic circle, no effect 

 was produced, either by the decomposition of water, or by 

 sensation on the tongue: nor was there any difference on re- 

 versing the poles. 



The iodine being now liquefied 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, instantly bubbles of 

 gas appeared and were evolved at the platinum wire, whilst 

 none appeared at the copper, being positive. The order be- 

 ing reversed, globules of gas appeared at both wires, showing 

 clearly that decomposition had been effected. 



Again, if the platinum wire be placed on the tongue, and 

 the copper wire be taken hold of with the hand, instantly the 

 galvanic sensation is felt. 



The heat being removed, the power of conduction gradually 

 dies away; so that in seven minutes it is incapable of 

 transmitting even sufficient electricity to be perceived by the 

 tongue. When therefore I stated in a note attached to Mr. 

 Solly's paper, that iodine when cold and concrete still con- 

 ducted, I was in error, being led to say so from recollection 

 only. But my general statement that iodine is a conductor, is, 

 I liope, satisfactorily shown to be borne out this day by ex- 

 periment. 



Dr. Cunmiing considered that the conduction might be 



3 II 2 



