On the Method of extracting Iodine from Kelp. 209 



pound it well in a mortar with water, and make it boil for half 

 an hour, stirring it continuaily with an iron spatula; we then 

 filter the mixture and set it to evaporate, taking care to lift up 

 with a skimmer the salts, a certain quantity of which the hot lye 

 allows to he deposited. If evaporated till crystalization takes 

 place by cooling, the salts become confounded in tlie crystalliza- 

 tion, and a great deal of iodate remains adhering to the crystals. 

 Tlie crystals, however weak may have been the lye in whicfh 

 they are formed, are always impregnated with iodate, which is 

 in a state of such strong combination, that these crystals, although 

 perfectly dried, redden strongly with sulphuric acid. It is bet- 

 ter, therefore, to allow the salt to be deposited in the hot lye, 

 where the muriates are not much more soluble than in the cold 

 lye, where the iodate remains a much longer time in solution. 

 The salt on being separated from the lye, and while it is still 

 hot, should be spread on a hair-sieve, where it mav dry itself. 

 When about half of the salt has been dried, it is put aside in or- 

 der to be afterwards pulverised and washed. The evaporation is 

 continued with the same precaution — that is to say, removing the 

 salt in proportion as the crystals are formed, until it ceases to 

 form any more. The lye is then united with the drain water, and 

 evaporated to dryness. A single lixiviation will then suffice to 

 exhaust the kelp of its swlt. 



We would advise that this salt should not be thrown away, as 

 there still adheres to it a good deal of iodate, until it has been 

 passed through a hot funnel. As the first crystallizations of this 

 salt redden with sulphuric acid as much as the last, they equally 

 contain iodate, which it is necessary to separate. For this pur- 

 pose the salt is well shaken in large glass funnels ; and by little 

 and little warm water is ])assed though it, trying at each washing 

 whether the salt continues to redden with sulphuric acid. 



The residue of thelve evaporated to dryness gets soon damp 

 in the air. It is necessary, therefore, to preserve it in flasks well 

 corked, if the iodine is not immediately wanted : when the latter 

 is the case, the residue is put into an earthen pan, and pounded 

 continually, incorporating with it by instillation concentrated sul- 

 phuric acid ; we say by instillation ; for if a drop of acid rests on 

 the place where it falls, a spot of iodine is soon manifested, and 

 a degree of heat developed which it is of importance to avoid. 



When enough of acid has been added to decompose the mu- 

 riate and the iodate, the mixture is transferred to a glass or 

 earthen alembic in order to be distilled. The heat at first being 

 moderate, ought not to be carried to that degree of ebullition that 

 no more muriatic acid is seen to pass, otherwise the iodine, which 

 at that temperature instantly evaporates, may be in part dissolrdd 

 by that acid. 

 ' Vol. S5. No. 2C3. March 1820. O After 



