CHEMICAL SCIENCE. 183 



iodine and bromine in the coals of Silesia, will suffice to draw the at- 

 tention of geologists to the confirmation which they furnish of the 

 ideas of M. Forchhammer respecting the formation of the aluminous 

 schists. Suanberg's Jahresbericht . 



ON A DIRECT METHOD OF OBTAINING IODINE FROM CERTAIN 

 SPECIES OF SEA-WEED ON A LARGE SCALE, WITH A MODE 

 OF PROCURING IT AS A SUBSIDIARY PRODUCT ADAPTED TO 

 COAST FARMS. 



THE following- is a summary of a research on the above subject, 

 made in the Isle of Man, by Dr. George Kemp, the principles of 

 which are applicable to all localities similarly situated. Marine vege- 

 tables on all sea-coasts may be classified according to the depths at 

 which they are found, but for the present purpose it will be merely 

 necessary to include them under two general classes, the shallow and 

 deep water sea-weeds ; the former embracing such growths as flourish 

 between high and low water-mark, and the latter such as are prin- 

 cipally found from low-water-mark to the depth of three or four 

 fathoms. As the general result of analysis it may be stated, that the 

 metallic base preponderating in the Fuci, or plants of the first class, is 

 sodium combined with chlorine, and small quantities of iodine and 

 bromine ; whilst the plants of the latter class, or those which flourish 

 in what Professor Forbes has denominated the Laminarian region, are 

 characterized by containing a preponderating quantity of potassium, 

 with a far larger proportion of iodine than in the former species, and 

 on this account are of more interest and importance to the manufac- 

 turer. In the earlier periods of the growth of the sea-weed, iodine is 

 almost entirely absent; it increases, however, with the advance of the 

 plant, and reaches its maximum at the precise period when the plant 

 yields to the autumn tempests and is drifted on shore, thus saving the 

 expense and risk of collecting from the rocks. The present method 

 of extracting iodine is by what is called the " kelp process," which 

 consists in burning the weeds, lixiviating the ashes, and collecting the 

 iodine from the mother-liquor by precipitation or distillation. To this 

 plan there are many objections, arising chiefly from the difficulty in 

 drying the weeds without inducing decomposition, from the tendency 

 of the iodine to volatilize during combustion, and from the loss in the 

 collection from the mother-liquor. To discover a better process was 

 the object of Dr. Kemp. By examining a section of the stem of the 

 Laminoria digttata, a species growing in deep water, he found that 

 the iodine was enveloped in cells situated between an external thin 

 cortical layer and a medullary central portion of the stem. This was 

 an important discovery, and hopes were entertained at first that the 

 iodine would be entirely liberated with a liquor yielded on subjecting 

 the plant to pressure ; but so condensed was the cellular tissue found, 

 that it gave up, when subjected to great pressure, but comparatively 

 little fluid. It was therefore determined, as the next experiment, to 

 break up the cellular tissue as completely as possible, by rubbing the 

 stem on an ordinary domestic grater. The result was perfectly satis 



