In the Canary and Cape de Verd Islands, as well as in the Grecian Archipelago, orchall is found in great abundance. It likewise grows in Guernsey and in some parts of England, and is employed by dyers chiefly for giving a bloom to other colours. This is effected by passing the dyed cloth or silk through hot water slightly impregnated with it; but the bloom thus communicated soon decays after it has been exposed to the air. When prepared in a peculiar manner, orchall yields a rich purple tincture, fugitive indeed, but very beautiful. Mixed with a solution of tin it is said to dye a permanent scarlet. Orchall is the substance generally adopted for colouring the spirits of thermometers. And it is a remarkable circumstance that, as exposure to the air destroys its colour upon cloth, so the exclusion of the air produces, in a few years, a like effect upon the fluid in those tubes; but on breaking the tubes the colour is restored. 287. _ICELAND LICHEN_ (Lichen islandicus) _is a leafy, membranous, vegetable production, of brownish green colour, jagged at the edges, and fringed, having large and purplish brown saucers or shields._ The name of this lichen is derived from that of the island in which it chiefly grows. It is, however, also found in the Highlands of Scotland, and in some of the northern parts both of England and Wales. It abounds with nutritious mucilage; and, after having been steeped in water to extract its bitter and laxative qualities, it is sometimes used as medicine in coughs and consumptions. One ounce of Iceland lichen, boiled in a pint of water, yields about seven ounces of mucilage. The inhabitants of Iceland prepare from it a kind of gruel, which they mix with milk. They also boil it in several waters, and then dry and make it into bread. In Germany a durable brown dye is made by means of it; and, under another mode of preparation, it imparts an excellent black tinge to white woollen yarn. 288. _BLADDER FUCUS_ (Fucus vesiculosus) _is a species of sea-weed, of flat shape, with a middle rib, the edges entire, forked, and sometimes tumid at the ends, and furnished with several air bladders imbedded in the substance of the plant._ By far the most important application of this, one of the commonest of all our marine plants, is for the making of _kelp_, which, in Scotland, affords employment to many industrious families. So lucrative and so highly esteemed is the bladder fucus, and some other plants nearly allied to it, that the natives of several parts of the Western Islands have rolled large masses of stone into the sea, with a view to promote and extend their growth.