Kelp is a natural danger-signal, and the sunken rock, " Uranie," is reputed to be the only one not buoyed by the giant seaweed.
Kelp and upland geese abound, the latter being edible; and their shooting affords some sport.
Courtois isolated the element iodine from " kelp," the burnt ashes of marine plants.
The linen trade introduced in the middle of the 18th century is extinct, and a like fate has overtaken the kelp and straw-plaiting industries.
In ocean water the ratio of soda (Na 2 O) to potash (K 2 0) is loo: 3.23 (Dittmar); in kelp it is, on the average, ioo: 5.26 (Richardson).
Courtois when investigating the products obtained from the mother-liquors prepared by lixiviating kelp or burnt seaweed, and in 1815 L.
Iodine is obtained either from kelp (the ashes of burnt seaweed) or from the mother-liquors obtained in the purification of Chile saltpetre.
The product obtained after burning is known either as kelp or varec. Another method of obtaining kelp is to heat the seaweed in large retorts, whereby tarry and ammoniacal liquors pass over and a very porous residue of kelp remains.
A later method consists in boiling the weed with sodium carbonate; the liquid is filtered and hydrochloric acid added to the filtrate, when alginic acid is precipitated; this is also filtered off, the filtrate neutralized by caustic soda, and the whole evaporated to dryness and carbonized, the residue obtained being known as kelp substitute.
The kelp obtained by any of these methods is then lixiviated with water, which extracts the soluble salts, and the liquid is concentrated, when the less soluble salts, which are chiefly alkaline chlorides, sulphates and carbonates, crystallize out and are removed.
The kelp industry, formerly of at least minor importance, has ceased.
The ash of seaweeds, known in Scotland as kelp, and in Brittany as varec, was formerly used as a source of iodine to a greater extent than is at present the case.
Among the marine productions on the southern coast, a species of kelp, Macrocystis pyrifera, merits special mention because of its extraordinary length, its habit of clinging to the rocks in strong currents and turbulent seas, and its being a shelter for innumerable species of marine animals.
Its chief commercial sources are the salt deposits at Stassfurt in Prussian Saxony, in which magnesium bromide is found associated with various chlorides, and the brines of Michigan, Ohio, Pennsylvania and West Virginia, U.S.A.; small quantities are obtained from the mother liquors of Chile saltpetre and kelp. In combination with silver it is found as the mineral bromargyrite (bromite).
It was hard, smooth sand, very different from the loose, sharp sand, mingled with kelp and shells, at Brewster.