208 On the Method of extracting Iodine from Kelp. 



The second process is attended with the inconvenience of sub- 

 jecting a large mass of salt to the decomposing action of sulphu- 

 ric acid, before the latter can begin to operate upon the iodate; 

 for it is not till after the other salts, and especially the muriates, 

 are decomposed, that an excess of sulphuric acid attacks the 

 iodate of potash, and separates from it the alkali, which at the 

 same instant oxygenizes itself at the expense of a portion of the 

 same acid. If in place of muriates the solution contain^ nitrates, 

 the decomposition of the latter suffices to oxygena'ic the iodic 

 acid, on account of the facility with which the nitric acid suscep- 

 tible of suboxygenation gives forth its oxygen. By extracting 

 from the lye nothing but the sub-carbonate of soda, we obtain 

 what is of little or no use; for the different sodas of Normandy, 

 with which we have made experiments, do not even contain as 

 mueh of this salt as will produce a change in the tincture of cur- 

 cuma. How, besides, can it Ije conceived that there exists at 

 the same time in a lye a free alkali and deliquescent muriates ? 

 The express condition that the muriates shall be decomposed 

 previous to the iodate, occasions an excessive expenditure of acid, 

 besides the inconvenience of prolonging the operation, and al- 

 lowing much iodine to escape, if the precaution is neglected of 

 not allowing the matter to get into ebullition before the greater 

 part of the muriatic acid is expelled. 



The process in which they mingle the superoxide of manganese 

 with the residue is scarcely any better ; it occa'jions a production 

 of chlorine which contains the iodine in combination. The addi- 

 tion of the superoxide may be more or less permitted, where iodate 

 exempt from m.uriate is made use of; the superoxide may then 

 serve rather to regenerate the sulphuric acid by the oxygenation 

 of the sulphurous acid, than to oxygenate the iodic acid. This 

 addition, taking care not to add at once all the sulphuric acid, 

 may further have the effect of facilitating the separation of the 

 muriatic acid, by converting it into chlorine ; but the presence 

 of chlorine produces such a disposition to the formation of iodine, 

 and the affinity between the two bodies is so manifest, that a 

 very great loss of iodine must be expected. 



We shall not say any thing of the process by which the iodate 

 of potash is isolated by means of alcohol : it requires that the 

 muriates of lime and magnesia contained in the lye should be 

 previously decomposed by the subcarbonate of potash; otherwise 

 these muriates, being soluble in alcohol, would become confound- 

 ed with the iodine. Besides, this process can only be employed 

 in demonstrations. 



Our results are infinitely more advantageous. We reduce the 

 rough kelp into powder, and pass it through a hair-sieve ; when 

 it is not dry enough to be tubmitted to that pulverization, we 



pound 



