Page:Popular Science Monthly Volume 36.djvu/392

378 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