456 Mr. J. Brown on .the Role of 



but also to some extent with the iodine, the solution of zinc 

 iodide so formed dissolving some reduced iodine to form the 

 brown-crimson solution frequently accompanying the action. 

 It is possible the deposition of the iodine crystals, almost in- 

 variably at a distance from the zinc, points to the existence of 

 a polarized molecular chain like that figured by Faraday as 

 connected with electrolytic action and referred to before, § 4. 



14. When the zinc was connected to a strip of platinum, 

 also dipping in the iodine-chloride solution, the iodine de- 

 posited partly on the platinum and a cell was formed as at 2, 

 Table I. 



For obvious reasons this cell differs from those in wdrich 

 hydrogen as cation is evolved in the free state in that it re- 

 covers its original electromotive force almost immediately 

 after temporary short-circuiting. Compare § 11. 



15. From the observations (§§ 10, 11, 12) and from thermo- 

 chemical considerations we may, I think, conclude that, of the 

 compounds present in the dilute solution, IC1 is the chief, if 

 not the only, one primarily concerned in the electrolysis, and 

 the one on which the character of the cell depends. 



16. The electromotive force. of cells containing IC1 in this 

 solution and otherwise are given in Table I. The forms 

 of cell tested contained one, two, or three electrolytes in 

 series between the positive and negative plates. The affix 

 "Aq" signifies an aqueous solution. This was in all cases 

 saturated, or nearly so, except those in column 4, and also 

 No. 2, Table I. The liquids were contained in a V-tube of the 

 ordinary kind if their respective specific gravities admitted of 

 this arrangement. If not, an inverted V-tube (A) was used 

 with an opening at its apex. The metals in wires or strips (not 

 specially pure) were fixed in corks in its ends. The electro- 

 motive force was estimated by comparison of the deflexions 

 produced in a Thomson Quadrant Electrometer by the experi- 

 mental cell and by a standard Daniell (pure copper in saturated 

 copper-sulphate solution and pure zinc in dilute solution of 

 zinc sulphate), which would, according to Dr. C. R. Alder 

 Wright's calculation*, have a force of about 1*13 volt. 

 Where several values for one cell are given, each is the result 

 of a separate and distinct experiment. 



17. Bromine chloride, Br CI, gives off exceedingly irri- 

 tating fumes, and is therefore very difficult to work with. 

 Most of the experiments were made with a purchased sample, 

 which was of a reddish-brown colour. As it is rather un- 

 stable, in order to check the first results a fresh quantity was 

 subsequently made by passing dried chlorine through bromine 



* Phil. Mae. [5] xiii. p. 284. 



