152 Proceedings of the Royal Irish Academi/. 



XXV. — On the Exteaction op Iodine and Eeomine eeoii Kelp. By 

 EoBEET Galloway, P. C. S., Professor of Chemistry in the Eoyal 

 College of Science for Ireland. 



[Keacl, April 8, 1878.] 



Hating had, some time ago, facilities for becoming completely ac- 

 quainted with the manufactming processes followed for the extraction 

 of iodine, bromine, and the potash salts from kelp, I devoted a consi- 

 derable portion of time to the study of this branch of manufacturing 

 industry. It is one of the manufactures which ought to floimsh in 

 Ireland, owing to the large quantity of the raw material (sea- weed) 

 which can be obtained in this country. I am sorry to have to state 

 that there is now no kelp factory in Ireland ; the only buyers of Irish 

 kelp at the present time are the Scotch manufacturers. 



The description in works on Chemistry, of the processes followed 

 for the extraction of the kelp products, are very meagre in a manu- 

 facturing point of view, especially as regards the extraction of the 

 two most valuable substances, iodine and bromine, and these two sub- 

 stances are the most difficult to extract with manufacturing success. 

 The descriptions state that such and such processes are followed ; but 

 important details are altogether omitted, as, for instance, the condi- 

 tions most suitable for carrying out the processes successfully, and the 

 different precautions which ought to be observed. 



Iodine was at one time a monopoly. The iodine manufacturers com- 

 bined together not to sell this substance under a certain price ; which, 

 like almost all other monopolies, had the effect of impeding rather 

 than of promoting improvement in this branch of manufacture. The 

 monopoly exists, I believe, no longer : new sources of supply of the 

 substances I have termed kelp products — iodine from the mother 

 liquors obtained in refining the nitrate of soda in Peru, bromine and 

 potassic chloride from the salt beds in Prussia — have not only extin- 

 guished it, but have also rendered necessary the" adoption of superior 

 and more economical methods in the extraction of these substances from 

 kelp, for the continuance of kelp being employed as a raw material. 



Many methods have been proposed for the extraction of the two 

 metalloids, iodine and bromine, from the ash of sea-weed ; but the 

 only one, as far as I am aware, which has been followed in the United 

 Kingdom, at least up to a very recent period, is the one ascribed to 

 "WoUaston. By this method they are set free from the metals with 

 which they are combined by the addition of sulphuric acid and man- 

 ganese peroxide to the mother liquor which remains after the extrac- 

 tion (of course as far as it is practicable) of potassic sulphate and 

 chloride, and what are termed the kelj) salts, which are a mixture of 

 sodic sulphate, carbonate, and chloride. 



The sulphuric acid is added for a twofold purpose : a portion is 

 required for the decomposition of the alkaline sulphides, sulphites, 

 and hyposulphites, present in the mother liquor; the other portion, 

 along with the manganese oxide, liberates the iodine and bromine 

 from their combinations. "When the sulphiu', wliich is set free fi'om 



