Popular Science Monthly/Volume 36/January 1890/A Harvest from the Ocean
By Prof. C. MORTON STRAHAN.
THE compensations of nature are nowhere more forcibly illustrated than along the bleak and rugged coasts of Scotland, Ireland, and Brittany, and their adjoining islands. Towering cliffs, whose scarred faces show no sign of verdure and defy all hope of cultivation, clasp the deeply indented bays in rude embrace. Hamlets by the score hide themselves in the more sheltered nooks, and the inhabitants find a precarious living by following the sea. Amid such unpromising surroundings Nature yearly plants and nourishes beneath the waves and along the wave-washed rocks a bounteous crop of sea-weed, which proves a genuine blessing to the dwellers on those shores. Not only is this both planted and nourished by the ocean, but it is to a great degree harvested by the same hand, and laid ready for use at the very doors of the fisherman's hut. The terrible storms which drive the venturous seaman against hidden rocks, sweeping ashore his lifeless body and dismembered ship, also tear up great quantities of this valuable weed from the ocean's bed and dash them in continuous bulwarks high up on the beach. Thus thrown ashore during the winter and early spring is a mass of what the natives call "deep-sea tangle," but which in the hands of the naturalist is recognized as a mixture of two kinds of Algæ, termed respectively Laminaria digitata and Laminaria saccharina. In the spring and fall the milder storms add the "tangle-top" to the winter harvest. The tangle-top, as its name implies, consists of the tops or fronds of the same plants whose stems compose the "tangle" proper. These self-gathered masses constitute the greater bulk and the more valuable part of the annual yield. Together they are known as "drift-weed," as opposed to three varieties of Fuci (more commonly known as wracks) which grow on the rocks in that area covered by the rise and fall of the tides, and which, from the manner of their gathering, take the name of "cutweed."
Recourse must be had at this point to chemical analysis to reveal some useful ingredient which may justify this wet, salty, ill-odored mass of vegetable matter being dignified by the name of a crop. The analyses of the several species of Laminaria and Fuci show considerable variations; it may, however, be taken that of the ordinary mixed mass of wet tangle and cut-weed about eighty per cent is water, fifteen per cent organic matter, and five per cent ash or mineral matter. In the same way it may be admitted that one hundred pounds of the ash will contain, approximately, twenty pounds of insoluble material, fifty pounds of alkaline carbonates and chlorides, twenty-two pounds of potash and soda, 6·5 pounds of sulphuric acid in combination, and 1·5 pound of iodine in combination as iodides of potassium, sodium, etc. One hundred and fifty years ago such an analysis had never been made, nor would it have possessed any of its present suggestiveness, for at that time iodine had not yet been discovered, and the burning of sea-weed for its ashes was practiced to but a very limited extent. It required the pressure placed upon the soap-makers of France and England by the wars of the great Napoleon to force practical and wide-spread attention to the ashes of sea-weed. In virtue of that pressure the foreign supply of soda and potash salts in both of those countries was entirely cut off, and every domestic substance was ransacked for its contents of alkalies. This gave rise to that general movement among the Scotch and Irish peasantry which resulted in the annual burning of the sea-weed harvest, and the introduction of a new commercial body under the name of varec or kelp.
Though the absolute yield of the alkali salts was small (about fifty pounds to one ton of the wet weed), so complete was the embargo against Spanish barilla and salt that kelp assumed a value as high as one hundred dollars per ton. During this halcyon period Scotland and her western isles reaped an annual income of nearly three million dollars, a sum which raised to affluence many a Scottish lord whose sole possession hitherto had been a long title and a few miles of barren sea-shore. But the end of the war, and the success of Le Blanc's process for making sodium carbonate out of common salt, brought down the value of kelp with a sudden and disastrous drop. In 1831 the price had fallen to ten dollars per ton, a figure no longer remunerative. At this period kelp-making would have died out entirely but for the presence in it of a small quantity of iodine. The discovery of that element in 1812, by Courtois, and the demands for its manufacture, which had arisen between that date and 1840, were the sole cause for the continuance of kelp-making; for kelp was then, and has since remained, the only practicable source of iodine in Europe. During the past fifty years kelp has furnished fully ninety per cent of all the iodine and iodides which commerce has handled. The remaining ten per cent comes from South America, being derived from the well-known caliche of Peru. This substance, in being worked for the large amount of nitrate of soda it contains, also gives a small quantity of iodine as a profitable by-product. The caliche yields from two to three pounds of iodine per ton, against an average yield of twelve or fifteen pounds on the part of kelp. Many bothering questions of manipulation increase the labor and cost of the product from the former source, thus leaving the commercial advantage with kelp. With the origin of this new demand for kelp the industry received a strong impulse, and the price was restored to fairly profitable figures, ranging from fifteen to twenty dollars per ton, at which price it is still in commerce.
It may be proper to note several interesting facts connected with the growth and composition of iodine-bearing weeds. All sea-weeds do not contain iodine, although that substance is universally present in sea-water in the ratio of one to two hundred and. fifty thousand, proportions which, though minute, are amply sufficient to tempt assimilation by all growing sea-plants at least to an appreciable extent. Yet very few of them outside the family of Algæ. contain even a trace of that element. So that to this family has been committed the chief work of withdrawing iodine from sea-water, and of concentrating it in plant-tissues in a form easy of extraction. The power of iodine absorption on the part of the Algæ is the more remarkable when it is remembered that their growth transpires in the presence of three hundred times as much of the very similar element bromine, which latter, however, is absorbed in only one tenth the quantity. The localities where they grow, as well as the number of iodine-bearing plants, are very limited. The shores of the British Isles and of Brittany are the spots most favored, owing to the presence of the Gulf Stream, which serves as the carrier of the iodine and of the temperature conditions necessary to the growth of the Algæ.
By far the larger portion of the sea-weed harvest comes ashore in the early spring and in the late fall. The fall harvest, together with that which winter adds, is suffered in most localities to lie untouched on the beach until it has been carried out to sea again and lost forever. It is only the spring crop which receives special care. Thousands of women and children, and a small sprinkling of men, may be seen flocking to the beach during the month of May, armed with rakes and wheelbarrows, or driving low carts, whose wheels are made broad enough to prevent their sinking in the sand. The wet weeds are raked into piles, and carried either by barrow or cart to a conveniently safe distance from the water's edge. Usually a sheltered nook is chosen, if near at hand, and in it is stored a great mass of the weed. Here it is left to dry under the summer 's hot sun, meanwhile exhaling odors of no dainty description. There are well-recognized liberties and restrictions in regard to sea-weed accorded to landlords and peasantry who dwell along the shore. The landlords have most of the liberties, while the peasants enjoy the restrictions. Conflicts of sea-weed rights have been known to occur, in which cases the shillalah has had an important share in the gathering of the crop.
When the weed is dry—that is, in the latter part of July and the first of August—the owners of the sea-weed heaps undertake to burn them into kelp. This burning is done in the crudest and most wasteful manner. Shallow pits, often dug right in the sand, are filled with weed and the mass ignited. Upon the first charge fresh quantities of weed are thrown from time to time, the whole mass burning more or less rapidly in proportion to the dryness of the weed. There results, in the bottoms of these pits, a black mass resembling iron-slag in appearance, though not in hardness, which, being sprinkled with water while hot, breaks up into large lumps suitable for transportation. Owing to the carelessness with which the weeds are raked up, this crude kelp-slag always contains a large percentage of sand and other impurities, sometimes amounting to one half the total weight of the product. The improvidence of this is the more marked in view of the small amount of valuable salts which even at best can be found in the kelp, and the rapid ratio in which the cost of transportation diminishes the profits when half of the slag is dead weight. The improvidence extends equally to the burning itself. This takes place in full access of air, and at a temperature so high as to volatilize much of the iodine. Besides, all the gaseous products of the combustion are lost and the escaped gases overcloud whole townships, and impart to miles of sea-shore the peculiar odor characteristic of burning kelp. To save these gaseous products by distilling the weeds in closed retorts, at low temperatures, would mean the production, at little extra cost, of valuable amounts of ammonia, parafin, acetic acid, naphtha, etc. In addition, the charcoal left would be much richer in iodine than the ordinary kelp, and its mechanical form much easier of subsequent extraction. Attention has been called time and again to the enormous waste of material and the easy means of improvement in kelp-making, but thus far little inroad has been made into this European species of ancestor-worship. The crofters cling to traditional methods and primitive tools.
When kelp, such as has been described, is brought into market, it is purchased by those directly engaged in making the salts of iodine and the alkalies. In their hands it becomes the subject of careful treatment to separate the valuable ingredients from the gross impurities with which they are associated. This is commonly done by breaking the kelp into small lumps and lixiviating in suitable vats filled with hot water or supplied with steam vapor. Such treatment, when sufficiently prolonged, dissolves out the alkaline and iodine salts, which need only the subsequent operation of being allowed to settle and siphoning off to separate them from the insoluble matters. The liquor contains chiefly the chlorides, the sulphates, the sulphites, and the hyposulphites of sodium and potassium, as well as the iodides and bromides of those metals. By evaporating this solution, the greater portion of the chlorides and sulphates will crystallize out before the iodides, bromides, and lower sulphur compounds begin to deposit. The former may then be fished out of the evaporating pan, leaving a resultant mother-liquor rich in iodides. The hurtful sulphur compounds remaining are decomposed by excess of strong sulphuric acid, and then the proper quantity of manganese dioxide is added. This mixture is transferred to an iron retort and heated, the result of which is to liberate the iodine and part of the bromine present. The vapors of these elements are conducted into proper earthenware condensers, where the iodine is deposited as a black powder, and the small quantity of bromine as a dense brown liquid moistening the iodine powder. As before indicated, from twelve to twenty pounds of this crude iodine are obtained from the mother liquor of one ton of kelp. There are several possible ways of purifying the crude iodine, in order to secure the iodine of commerce and also the bromine which had been its chief impurity. Even this purified iodine contains minute traces of bromine, owing to the difficulty of their perfect separation. If iodide of potassium is desired instead of free iodine, it is still necessary to produce the latter, and from it obtain the iodide by the action of potassium hydrate or caustic potash.
Iodine, as a commercial body, has been subject to great fluctuations in price. It has ranged from a minimum of $1.50 to a maximum of $9.50 per pound, and is at present quoted at the fairly constant figure of $4 per pound.
This harvest of sea-weed, whose transformation into iodine has been briefly traced, has been to a certain extent the subject of other industrial applications. In Ireland and the Channel Islands the weeds are used directly as a fertilizer. Its advantages in this line are chiefly felt in the Irish potato crop, where the potash of the sea-weed supplies a most important ingredient of that staple tuber. The presence, also, of small proportions of the earthy phosphates increases its value for fertilizing purposes. Attempts have been made to utilize these weeds in the manufacture of paper and textile goods, but with little or no success, owing to the fact that the true Algæ are not fibrous in their structure; nor is it surprising to find sea-weed quite extensively used as a fuel among a tenantry so poverty-stricken, and in a country so bare of combustibles. But the chief value of the sea-weed harvest remains in the monopoly of iodine which its tissues possess.
Despite its many wasteful drawbacks, the kelp industry shows the respectable annual yield of six million dollars, much of which finds its way into the pockets of a very destitute tenantry. In those districts where the winter supply is carefully gathered and burned, the production of kelp has had very beneficial effects by employing and remunerating the most indigent classes at a time when they would otherwise be totally unproductive.