THE 

 LONDON, EDINBURGH, and DUBLIN 



PHILOSOPHICAL MAGAZINE 



AND 



JOURNAL OF SCIENCE. 



[FIFTH SERIES.] 



APRIL 1886, 



XLI. On the Electromotive Forces developed during the Com- 

 bination of Zinc and Iodine in presence of Water. By 

 A. P. Laukie, B.Sc. Edin. y B.A. Cantab* 



THE following paper is a description of the measurements 

 of the electromotive forces of certain constant voltaic 

 elements, with a view to determine the heat of combination 

 of zinc and iodine in presence of water. 



As these measurements have been made in new voltaic 

 combinations, a few words may be devoted to describing the 

 forms of cells used. In the experiments described in the 

 sequel, two cells have been used, namely the zinc-iodine cell 

 and the zinc-cuprous-iodide cell. 



The zinc-iodine cell consists of a zinc rod and a platinum wire 

 immersed in a solution of iodide of zinc, in which free iodine 

 has been dissolved. During the passage of a current the 

 reactions which take place in the cell are very simple, zinc 

 and iodine combining to form iodide of zinc, which dissolves 

 in the water present. Thus as the zinc dissolves, the iodine 

 combines with it, and as long as free iodine is present the 

 cell is remarkably free from polarization. 



The cuprous -iodide cell consists of a zinc rod, and a copper 

 wire coated with cuprous iodide, immersed in a solution of 

 iodide of zinc. During the passage of the current the zinc 

 dissolves and the insoluble cuprous iodide is reduced to 

 metallic copper. 



* Communicated by the Author. The substance of a considerable 

 portion of this paper appeared in the ( Proceedings of the Koyal Society 

 of Edinburgh ' for 1885. 



Phil. Mag. S. 5. Vol. 21. No. 131. April 1886. Y 



