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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 41bs. 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
121bs. 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. |
