1265. Sea-weeds, consisting of different species of Fuci, A'lgï¾µ, and Confervï¾µ, are much used as a manure on the sea-coasts of Britain and Ireland. In the Orkney Islands the Fucus digitatus is preferred, on account of its greater substance. When driven on shore by the winter storms or the gales of spring, it is collected and laid on the land, into which it is then ploughed. In summer it is burnt, with other Fuci, into kelp. It is a powerful fertiliser, but its benefits do not extend beyond one or at most two seasons. By digesting the common Fucus, which is the sea-weed usually most abundant on the coast, in boiling water, one eighth of a gelatinous substance will be obtained, with characters similar to mucilage. A quantity distilled gave nearly four fifths of its weight of water, but no ammonia; the water had an empyreumatic and slightly sour taste; the ashes contained sea salt, carbonate of soda, and carbonaceous matter. The gaseous matter afforded was small in quantity, principally carbonic acid, and gaseous oxide of carbon, with a little hydro-carbonate. This manure is transient in its effects, and does not last for more than a single crop; which is easily accounted for from the large quantity of water, or the elements of water, which it contains. It decays without producing heat when exposed to the atmosphere, and seems, as it were, to melt down and dissolve away. A large heap has been entirely destroyed in less than two years, nothing remaining but a little black fibrous matter. Some of the firmest part of a Fucus was suffered to remain in a close jar, containing atmospheric air, for a fortnight: in this time it had become very much shrivelled; the sides of the jar were lined with dew. The air examined was found to have lost oxygen, and to contain carbonic acid gas. Sea-weed is generally used as fresh as it can be procured, but it is sometimes used with very great advantage as litter in the farm-yard, forming excellent manure with the dung of the cattle.
