THE MANUFACTURE OP KELP. 291 



The organic matter includes the charcoal and everything dissipated in 

 burning. In the analyses of the soluble portion of the ash, the potash and 

 sulphuric acid are stated separately, and the alkaline chlorides indicate the 

 total amount of chlorides of potassium and sodium, supposing the two 

 alkalies existed entirely as chlorides. This was considered the best means 

 of stating the results for comparison. A small proportion of carbonic acid 

 contained in some of the salts was not estimated, because practically it is 

 not separated. The kelp is the fused ash obtained in an open porcelain 

 crucible. The best seaweed for working commercially would be that con- 

 taining the most iodine and potash, and the least sulphuric acid. 



The estimations of iodine were the results of a separate set of experi- 

 ments, in which the weeds were carefully carbonised in a covered porcelain 

 crucible, at a low red heat. The iodides were dissolved from the charcoal 

 with water, and the iodine estimated as iodide of palladium. Thus treated, 

 the weeds were found to yield much more iodine than when burnt, even at 

 the same temperature, in an open vessel. "When thoroughly burnt, the 

 poorer weeds gave results which could scarcely be appreciated. Laminaria 

 digitata gave 19 per cent., or less than half the yield from the charcoal ; 19 

 per cent, corresponds to 1277 lbs. per ton of kelp, and the iodine usually 

 obtained from the best commercial kelp made from this weed seldom ex- 

 ceeds this amount. Mr. Paterson, who may be considered the highest 

 authority on this question, states the present yield of iodine from good drift 

 weed kelp to vary from 8 to 14 lbs., but the low quality of drift weed kelp 

 produced in the islands of North and South Uist, and the county of 

 Donegal, does not yield him more than from 4 to 6 lbs. per ton of 22J cwt. 

 He accounts for the bad quality of the kelp of Uist by the large admixture 

 of sand from the shores of those islands. It is probably also much mixed 

 with inferior seaweeds. The statement of the amount of iodine from the 

 Laminaria digitata is the average of three estimations, and to show the 

 amount that ought to be obtained from this species, I may state that this 

 corresponds to 32 lbs. of iodine per ton of kelp (20 cwt.) Many of the 

 analyses of seaweeds hitherto published have been performed on different 

 kelps, and as these always contain the ash of several species, little depend- 

 ence can be placed on them as an index of the relative composition of each 

 species. The plants here experimented on were carefully selected. The 

 amount of iodine will be seen to be exceedingly small in the Fucus vesieu- 

 losus, and kelp made from that seaweed alone would be valueless. It would 

 yield only -99 lb. per ton, but practically it always contains the ashes of 

 others sufficient to bring it up to about 4 lbs. per ton. Sarphati estimated 

 the iodine in this species to be "001 per cent. 



I would call attention to the large yield of potash from that very com- 

 mon weed, No. 7. The soluble ash it yields is very variable in quantity, the 

 fronds being always more or less covered with zoophytes, which largely 

 increase the amount of ash without adding to the soluble portion. The 

 results given are the mean of three analyses. The potash was in all cases 

 estimated as the double chloride of platinum and potassium. 



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