210 On the Method of extracting Iodine from Kelp, 



After iodine has ceased to be disengaged, in order to try if the 

 residue is exhausted, a new quantity of sulphuric acid is poured 

 upon it while it is still hot ; if at the moment of contact a white 

 vapour without any tinge of red arises, it is a proof that the iodine 

 is all disengaged. This white vapour is produced by an acid sub- 

 stance, in which we have recognised the following properties : It 

 does not dissolve iodine ; it possesses a flavour similar to that of 

 dilute sulphuric acid ; it gives no precipitate with muriate of ba- 

 rytes, but with nitrate of silver and the oxymuriate of mercury it 

 does (the latter precipitate of a pale red colour) ; and fills the at- 

 mosphere with the odour of chlorine. We purpose afterwards to 

 examine this product. 



The iodine may be disengaged at the same time with the mu- 

 riatic acid, and as soon as that acid, by applying at once a boiling 

 heat. The vapours which appear are violet, and the little mtt- 

 Tiatic acid which passes at the same time is not particularly co- 

 loured. It has been said, that at the degree of heat at which 

 iodine can be produced, the action of the sulphuric acid tends 

 rather to produce this body than to disengage the muriatic acid. 

 It is true that the strongest affinity is then in favour of the mu- 

 riates, and that the weakest acids, perhaps even sulphurous acid; 

 may decompose the oxygenated iodates. The operation, whatever 

 may be the quantity of salt, is finished in an hour at the most. 

 The saline residue, in an experiment which had been interrupted 

 after the disengagement of iodine, was composed in its liquid 

 part, which was decanted warm, of super-sulphate of soda and 

 super-sulphate of potash, besides free sulphuric acid ; the re- 

 maining'part, concrete when warm, consisted of muriate of potash 

 and muriate of soda. This proves that muriatic acid had con- 

 curred in the decomposition of the oxygenated iodate of potash. 

 It appeared singular that acidulated sulphates and free sulphuric 

 acid had been able to exist together, and to be heated to ebul- 

 lition, without being mutually decomposed. After having distin- 

 guished the different salts, we joined them to the mother-waters, 

 and distilled the mixture to drvness. A great deal of muriatic acid 

 passed, and there only remained neutral sulphates of potash and 

 soda. 



In a similar experiment, but which was not interrupted after 

 the disengagement of the iodine, a great deal of muriatic acid 

 passed at the distillation. This acid was absolutely colourless, 

 and almost without odour. However, a good deal of muriate of 

 iron was found in the residue, and the acid obtained had enough 

 of concentration to fume if it had been otherwise prepared. 



We made the experiment of washing with a little water the 

 rough kelp finely pulverised. The solution contained more iodate 

 and less of other salts than the lye made in a large quantity of 



water J 



