1911 Encyclopædia Britannica/Kelp

KELP (in M.E. culp or culpe, of unknown origin; the Fr. equivalent is varech), the ash produced by the incineration of various kinds of sea-weed (Algae) obtainable in great abundance on the west coasts of Ireland and Scotland, and the coast of Brittany. It is prepared from the deep-sea tangle (Laminaria digitata), sugar wrack (L. saccharina), knobbed wrack (Fucus nodosus), black wrack (F. serratus), and bladder wrack (F. vesiculosus). The Laminarias yield what is termed “drift-weed kelp,” obtainable only when cast up on the coasts by storms or other causes. The species of Fucus growing within the tidal range are cut from the rocks at low water, and are therefore known as “cut-weeds.” The weeds are first dried in the sun and are then collected into shallow pits and burned till they form a fused mass, which while still hot is sprinkled with water to break it up into convenient pieces. A ton of kelp is obtained from 20 to 22 tons of wet sea-weed. The average composition may vary as follows: potassium sulphate, 10 to 12%; potassium chloride, 20 to 25%; sodium carbonate, 5%; other sodium and magnesium salts, 15 to 20%; and insoluble ash from 40 to 50%. The relative richness in iodine of different samples varies largely, good drift kelp yielding as much as 10 to 15 ℔ per ton of 221/2 cwts., whilst cut-weed kelp will not give more than 3 to 4 ℔. The use of kelp in soap and glass manufacture has been rendered obsolete by the modern process of obtaining carbonate of soda cheaply from common salt (see Iodine).