588 Mr Connell on the Action of Iodic Acid 



destroy vegetable colours ; and even Berzelius has said that the 

 aqueous solution of iodine does not bleach vegetable colours*. 

 From the experiments, however, which I have made, it appears 

 that the aqueous solution of iodine, notwithstanding the very 

 small quantity of iodine which it contains, destroys vegetable co- 

 lours to a very great extent, when added in sufficient quantity, 

 although the bleaching is not absolutely perfect. The solution 

 employed was prepared in two ways ; first, by boiling distilled 

 water on the iodine of commerce, until it became of a decided 

 yellow colour; and, secondly, by dissolving freshly, sublimed 

 iodine in alcohol, precipitating it by water, washing it largely 

 with the latter fluid, and then allowing water to stand on the 

 finely divided iodine thus obtained, in which case it readily be- 

 comes yellow by dissolving the iodine even in the cold. The 

 second method was followed with the view of purifying the 

 iodine, but the results are the same whichever method is fol- 

 lowed. When blue cabbage infusion was treated with five or 

 six times its bulk of the solution of iodine, the blue colour en- 

 tirely disappeared, and a very feeble reddish or yellowish tint 

 only remained. The effect is best seen by diluting a corres- 

 ponding portion of the infusion with a quantity of pure water, 

 equal in bulk to that of the iodine water used, when the differ- 

 ence of result becomes abundantly manifest. When the infu- 

 sion of litmus was treated in the same way, the effect was just 

 the same. No colour remained except an extremely feeble 

 blackish tint. ^The bleaching action of iodine may also be exhi- 

 bited in the solid way. If a piece of this substance be dropped 

 into a little of the infusion of cabbage in a tube, the liquid will 

 be found to become gradually yellow, and, in the course of a 

 few days, the effect is completed. The colour of infusion of lit- 

 mus is also gradually destroyed by similar treatment, although 

 more slowly. These facts, tending to confirm the original state- 

 ment of M. Gay-Lussac, may perhaps not be deemed superfluous, 

 since that statement was made only generally, and the matter has 

 subsequently been differently stated ; and it cannot be a matter 

 of indifference to establish that two bodies, allied together by so 

 strong analogies as chlorine and iodine, agree also in possessing 

 the remarkable property of destroying vegetable colours. 

 " Lehrbuch der Chemie, i. 255. 



