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Transactions of the Highland and Agricultural Society of Scotland
On the Manufacture of Kelp


By Mr Donald M'Crummen, Ardintinny Cottage, Argyleshire.
[Premium—Medium Gold Medal.]

In reference to the Society's proposal for a report on the most economical and simple process by which iodine, and the valuable salts which accompany it, can be extracted from kelp, or seaweed ("especially as fitted to be carried on by the inhabitants of the Northern and Western Highlands and Islands of Scotland"), the author begs to state, that, from a variety of experiments, in which he has for a number of years been engaged, he is satisfied that the process of separating the salts in kelp cannot be carried on by the people in the kelp districts, as, even in the iodine works in Glasgow, and elsewhere, with all the advantages of perfect establishments for the purpose, considerable chemical knowledge and practical experience are necessary for carrying it on successfully.

The expense of working up a ton of kelp in Glasgow, and extracting therefrom the saleable ingredients, is about L.2; which, at the prices of 1846, is about the value of the salts of soda and of potash, which the ton contains; so that the makers must depend upon the price of iodine for the cost of the kelp and the profits of the business.

Ordinary cut-weed kelp has been found to yield from 3 to 4˝bs. of iodine per ton, and drift-weed from 6 to 10lbs. per ton. The price of iodine in 1845 was from 30s. to 40s. per lb., and in 1846 it was reduced to 16s., with a tendency to go still lower. The price in 1836 was as low as 6s. to 8s. per lb. These fluctuations show the great uncertainty of the trade, and the necessity of preparing the raw material at as low a rate as possible.

Now, it appears to the author, from experiments in which he has been recently engaged, that the soluble salts in seaweed can be procured by burning the dried weed into ashes, in the open air, and without applying the heat necessary to flux them. The salts procured from a solution of these ashes, contained all the ingredients usually found in kelp.

This leads the author to conclude, that the simple mode of burning the weed, lixiviating the ashes, and evaporating the solution to dryness, might be carried on by the country people.

The author has used for this purpose a small cast-iron boiler, and receiver, with three tubs, which cost about L.4. With this simple apparatus, the essential properties of two tons of kelp can be concentrated into one ton of salts, which might be worth to a chemical manufacturer (if made from cut-weed) L.5 to L.6; or from drift-weed, L.8 to L.10. If a poor crofter on the sea-shore could be put in the way of every year preparing a ton of this salt, it would be establishing a sort of domestic manufacture, which would be of incalculable advantage to him; and the suggestion in the Notice would apply—of making "one heap of sea-weed serve as fuel for evaporating the solution from the ashes of a preceding heap;" so that the process of burning the weed into ashes, and making the salt, could go on simultaneously, even under the roof of the cottager.

The country people, too, could be instructed to adopt the plan recommended by Dr Traill in a paper which was published in the "Transactions" in July 5, 1833, of using peat and ferns, to increase the salts of potash.

The author has found that burning heather with the seaweed would also increase this salt. Of heather they have an unlimited command in the Highlands.

Whatever is added to increase the salts of potash, will increase the salts of soda at the same time, by a double decomposition, well known to chemists.

The insoluble portion of these ashes would be invaluable manure for the land of these poor people, as they contain many of the properties which Professor Johnston will find entitled to more investigation and attention than has hitherto been bestowed upon this matter.

The cut-weed kelp is generally made from Fucus vesiculosus, serratus, and nodosus; all of which grow nearest the high-water mark. The drift-weed kelp is chiefly composed of Fucus digi-tatus, which grows in deep water. It is a plant with large leaves, and strong stem, of which great quantities are cast on shore in stormy weather. It is found to yield the largest quantity of iodine; 8 and even 10lbs. per ton have frequently been obtained from it. And the author has analysed a sample made in Orkney, which contained at the rate of 12˝bs. per ton; but it had been cut from the rocks, and immediately dried and burned.

An iodine maker in Glasgow confessed to the author, that he had obtained the same produce from a parcel made in the west of Ireland, where the author knows it is the practice to cut tangle from the rocks in spring tides. The author has also seen drift-weed kelp from the islands of Benbecula and North and South Uist, which was found to contain 10lbs. to 121bs. of iodine per ton.

Although the author is satisfied, from his own experience among the people, that they could not be made to carry on the complex and intricate chemical process by which the salts in sea-weed are separated, he is sure that the proprietors of the extensive shores of the district of the Hebrides, called the Long Island (with which he is well acquainted), where formerly 4000 tons of kelp were made annually, could, with great advantage to themselves and their people, establish iodine works on their estates. Before doing so, however, it would be important for them to ascertain if iodine can be extensively used in the arts. The demand for the last four years, and consequent great advance in price, has been attributed to a discovery, said to be made by a French chemist, of a method by which the very brilliant colours which this substance produces, when in combination with the metals, can be permanently fixed; thus rendering it valuable as a dye-stuff.

The author has taken much trouble to investigate it, but cannot satisfy himself that this discovery has really been made. It would be of great consequence to the kelp proprietors to have this point investigated, as, while the use of iodine is confined to medical purposes, the consumption must be comparatively limited. Having been extensively concerned in the kelp trade, during its best days, and watched with painful interest its downfall, it would afford the author great pleasure, if he could be instrumental in reviving any branch of it that would again afford employment to the poor people.


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