Kelp

Kelp, the ash of various seaweeds prepared on the coasts of Scotland, Ireland, and Brittany, formerly as a source of carbonate of soda and now mainly for iodine. The chief algae employed are the "cut weeds," Fucus vesiculosus (bladder-wrack), F. nodosus (knobbed-wrack), and F. serratus (black-wrack),which are cut from the rocks between high- and low-water marks, and the "drift-weeds," Laminaria digitata (tangle), and L. saccharina (sugar-wrack). They are dried in the sun, and then, according to the more economical modern processes, destructively distilled. About 20 tons of sea-weed yield a ton of kelp. Drift-weed kelp will yield from 8 lbs. to 13 lbs. of iodine per ton; but cut-weed kelp much less. Nearly half the ash is insoluble, the soluble portion including 20 to 25 per cent, of potassium chloride, 10 to 12 per cent. of potassium sulphate, and 5 per cent. of sodium carbonate, besides other salts of sodium and magnesium. At the beginning of the century kelp was the main source of sodium carbonate, and some 20,000 tons wore made annually in Scotland, its value being £20 per ton. On the introduction of Leblanc's process for preparing sodium carbonate from common salt the value of kelp fell to £2 a ton; but it rose in value as a source of iodine. The total production of kelp in the British Isles is now from 7,000 to 10,000 tons annually, and its value about £4 per ton.