1281. Dung of birds. Amongst exerementitious solid substances used as manures, one of the most powerful is the dung of birds that feed on animal food, particularly the dung of sea-birds. The guano, which is used to a great extent in South America, and which is the manure that fertilises the sterile plains of Peru, is a production of this kind. It exists abundantly, as we are informed by Humboldt, on the small islands in the South Sea, at Chinche, Ilo, Iza, and Arica; it has been also found abundant on the island Ichaboo. Fifty vessels are laden with it annually at Chinche, each of which carries from 1500 to 2000 cubical feet. It is used as a manure only in very small quantities; and particularly for crops of maize. Some experiments were made on specimens of guano in 1805. It appeared as a fine brown powder; it blackened by heat, and gave off strong ammoniacal fumes; treated with nitric acid, it afforded uric acid. In 1806, Fourcroy and Vauquelin published an elaborate analysis of guano. They state that it contains a fourth part of its weight of uric acid, partly saturated with ammonia, and partly with potassa; some phosphoric acid combined with the bases, and likewise with lime; small quantities of sulphate and muriate of potassa; a little fatty matter; and some quartzose sand. It is easy to explain its fertilising properties: from its composition it might be supposed to be a very powerful manure. It requires water for the solution of its soluble matter, to enable it to produce its full beneficial effect on crops. The guano of South America, which was imported in such large quantities from 1842 to 1847, was the residue of the putrefaction of the excrements of sea-fowl, and consisted 'chiefly of various salts of ammonia, inorganic compounds, and undecomposed organic matters.' 'The salts of ammonia,' continues Professor Solly, 'dissolve easily in water, and are at once absorbed by plants, whilst the undecomposed organic matter, gradually undergoing decomposition, continues for some time to yield a regular supply of ammonia.' 'In using guano as liquid manure,' he continues, 'it must be remembered that the solution formed by pouring water over it only contains the ammonia and about one quarter of the phosphates; the rest of the phosphates, and the organic matter, being nearly insoluble in water; hence the residue is nearly as valuable a manure as that which is dissolved; and in order to derive the whole benefit from the manure, the insoluble part must, by agitation or other means, be kept suspended in the liquid whilst it is being spread over the ground.' (Solly's Rural Chemistry, 2nd ed., p. 185.)
