On i/ie Method of extracting Iodine from Kelp. 211 



water ; but there remained after this mode of extraction, still too 

 much iodate in the residue to make it of advantage to follow it. 



If the separation of the crystallizable salts is pushed too far, 

 and especially if it is sought to obtain them by the recooling of 

 the lye, nothing, as we have said before, will be preserved but a 

 mother-water exhausted of iodate, and which will not yield the 

 least part of iodine. It is from not finding iodine in the mother- 

 water of a soda known to contain it, that we have thought of 

 seeking for it in the crystallized salt. 



It has been stated that, from Scotch kelp, iodate of soda as 

 well as iodate of potash may be extracted. That kelp cannot 

 therefore reckon amongst its salts either the sulphate or muriate 

 of potash, which would l)e decomposed by the iodic acid of the 

 iodate of soda, although there may be found in the same lye 

 the sulphate of soda and the muriate of potash. It is impossi- 

 ble, however, to admit, as some authors have done, the exist- 

 ence of these different salts with the iodates of magnesia and of 

 lime. 



The soda with which we have experimented was of the species 

 known in commerce under the name of common soda of Fecamp. 

 The pieces recently broken presented in their fracture a blueish 

 gray colour j they were besprinkled with oparjue white crystalline 

 knots ; the parts which had been exposed to the contact of the 

 air were humid, of a black colour, and contained also knots of 

 salt. Their lye gave about a fourth of their weight in saline pro- 

 ducts, but no sub-carbonate of soda. The water of a first cold 

 washing contained muriate of lime, and the lye obtained by boil- 

 ing contained muriate of magnesia. The former muriate was no 

 longer to be found in the lye, having been decomposed by the 

 sulphate of soda. Common soda preserved for thirty years, and 

 which after being damped was completely dried, did not yield less 

 iodine than kelp newly bought. In Belgium, where considerable 

 use is made of kelp for the fabrication of common glass, it is 

 found to give a very good frit, and tliat the salts supply to that 

 what it wants of alkali ; the solution of its residue after the sepa- 

 ration of the iodine, leaving on the filter a good deal of silex. The 

 alkali may be considered as being partly in the state of liquid 

 silicate ; which explains how its lye in the neutral alkali saturates 

 a certain quantity of acid. 



We have tried to decompose at the outset the muriatic salts, 

 by pouring into the lye a quantity of sulphuric acid — at first, be- 

 cause that method accelerated the operation — afterwards, because 

 we found that in operating with a salt which is not very dry, or 

 which has got moist in the air, the muriatic acid which passes, 

 and the expulsion of which demands a greater degree of heat, is 

 always much coloured with iodine; but we have in cxjierinients 



O 2 on 



