the Cation in Voltaic Combinations. 453 



The resulting solution therefore contains iodic acid and the 

 double chloride of hydrogen and iodine, which is stable in 

 water. If, however, the iodine chloride contains in addition 

 to the mono- a higher chloride, and there is sufficient chlorine 

 present to form the double chloride HCl . IC1, no iodine is pre- 

 cipitated and only iodic acid and the double chloride are formed. 

 The first portion of iodine chloride I obtained, and from which 

 the aqueous solutions were made, was probably of this kind. 

 The makers (Irish) stated that it probably contained IC1 3 . It 

 was in red-brown crystals, and left only a slight yellowish 

 residue on dissolving in water. Its solution will be referred 

 to for convenience as iodine-chloride solution, see § 15. 



11. When electrolysed between platinum poles it deposited 

 iodine at the cathode, sometimes in long filaments, and gas 

 at the anode. When a gradually increasing E.M.F. was 

 applied to the platinum poles, it was found that the ratio of 

 the electrolysing current to the applied E.M.F. began to 

 increase very rapidly at about *12 D., which corresponds 

 nearly with the ratio of the combining heat I, CI to the heat 

 equivalent of the Daniel], and indicates the beginning of 

 regular decomposition of that compound. The small current 

 at lower E.M.F.s may readily be connected with the electro- 

 lysis of impurities in the solution or the action of dissolved 

 oxygen. The ratio of the current to the applied E.M.F. is 

 considerably greater after '2D. till '25 D., where the experiment 

 ended. The corresponding curve is shown in fig. 3, p. 458. 



On testing the secondary E.M.F. of this arrangement, it 

 was found that immediately on removing the applied E.M.F. 

 the electrometer deflexion decreased (rapidly at first) to a 

 point of moderate permanence which varied with the pre- 

 viously applied E.M.F. and current that had passed. It 

 indicated a secondary E.M.F. which (as would be expected 

 from the low combining heat I, CI) was small and did not in 

 any case exceed *2 D. 



When an intermediate tapping pole was used to test the 

 secondary E.M.F. at the anode and cathode separately, it was 

 found that the principal and more permanent effect was at the 

 anode (from the chlorine probably), whereas that at the 

 cathode was only from *1 to *2 of the whole and more 

 evanescent. This might a priori be expected, since iodine is 

 not a conductor nor very soluble in the liquid, nor is it likely 

 to alloy with the platinum by occlusion like hydrogen, but 

 simply forms a loose deposit not well adapted to take any 

 further part in electrolytic action. 



12. A strip of zinc immersed in the saturated solution was 

 scarcely attacked at first, but merely caused a slight whitish 

 deposit (? iodate of zinc, compare § 25). Afterwards iodine 



