The existence of bird-guano on the Jardinillos, a group of islands to the south of Cuba, has long been known, but only recently examined. Analyses from various portions give the following results : — Cayo Largo : N.-W., phosphoric acid, 24.02 per cent., = phosphate of lime, 52'43 ; W., phospholic acid, 29.33, = phosphate of lime, 64.03 ; S. and S.-W., phosphoric acid, 28.98, = phosphate of lime, ; Cayo Dios : (a) phosphoric acid, = phosphate of lime, 62.94 ; (b) phosphoric acid, 26.53, = phosphate of lime, 57.92. The deposits are now to be worked for supplying the sugar and tobacco plantations, almost the whole of the phosphate being present in a soluble condition.
In many caves in Virginia and Texas, are found extensive deposits of bat-guano, in some instances amounting to several thousand tons. The deposits exhibit a dull-brown colour, and become finely pulverulent when dried in the air. They consist of the excrement of bats, more or less contaminated with soil, and their chemical composition places them almost on au equality with modern Peruvian guanos. Attempts to utilize them for the preparation of nitrate of potash, for gunpowder-making, have not been successful.
The climate of parts of the African continent also favours the preservation of guanos ; but if the deposits are allowed to remain for any great length of time, they lose almost all their nitrogen. Thus, the now exhausted deposits from Ichabo and Saldanha Bay contained respectively but 6 per cent. and 11 per cent. of nitrogen ; while the fresh accumulations yearly formed there, and collected immediately, yield as much as 12 per cent, and 9 per cent, of nitrogen respectively. The water present is also reduced; in the first case, from 27 per cent. to 17 ; and in the last, from 22 to 12. The thinness of the recent deposits, however, makes it difficult to collect the material in a condition free from foreign bodies, such as sand and stones.
Small parcels of nitrogenous guanos have been derived from many other spots; the quantity has, however, been insignificant, and the list may be concluded with two kinds from the islands of the Pacific Ocean. That known as " Baker's Island " contains nearly 35 per cent. of phosphoric acid ; while " Jarvis Island " shows little over 20 per cent. of that element. In neither case, does the nitrogen exceed per cent. These guanos have found a market in Germany, but aro very little known in this country.
Artificial term " artificial " is applied to those manures which are never used save in a manufactured state. They may be conveniently divided into two classes, ammoniacal and phosphatic : the former represented by sulphate of ammonia; the latter, by the various kinds of superphosphates, nitrophosphates, bone-manures, turnip-mannres, &c.
Sulphate of Ammonia.—In the distillation of coal for the production of illuminating-gas, the nitrogen is liberated as ammonia. This is retained in the water which is distilled over, and in the se-called " gas-liquor," from the scrubbers through which the gas is passed (see Ammonia, p. 246). The proportion of ammonia held in these liquids will naturally depend upon the character of the coal used. The ammonia thus recovered exists principally as carbonate, with smaller quantities of hydrosulphate, sulphate, hyposulphite, sulphocyanate, and chloride, of ammonium. This last salt in some cases represents 50 per cent. of the total amount of ammonia compounds procured in the water distilled with the gas, none but volatile salts being absorbed in the wat,4. descending through the scrubbers. Gas-liquor may be used directly as a liquid manure, provided it does not contain an appreciable amount of sulphocyanates (which are highly poisonous to vegetable growths), and that it be considerably diluted with water. It is far more common, however, to distil the ammonia from the liquor, and to collect it in sulphuric acid, as sulphate of ammonia. This salt is sold commercially on a guaranteed basis of about 24 per cent. of ammonia, or more than 93 per cent. of pure sulphate. When the proportion of nitrogen is very large, sulphocyanates may be suspected. Their presence may be detected by the formation of a blood-red colour on the addition of ferric chloride Co an aqueous solution. If phosphates exist in the solution, the reaction can be observed only in the presence of hydrochloric acid.
The spent oxide of iron used for purifying gas also contains some ammonium salts, principally sulphate, with a little sulphocyanate. This may be washed out and utilized.
When the gas is purified by sawdust soddened with sulphuric acid, the purifier will contain, when dry, about 12 per cent. of nitrogen, which is equivalent to more than 50 per cent. of ammonium sulphate. It is not all present as sulphate, however, cyanides and sulphocyanates existing also ; but it is said that the sulphocyanic acid evaporates by keeping the material in bulk for some time, and, being very volatile, it can certainly be easily expelled by hydrochloric or sulphuric acid in the presence of heat.
Commercial sulphate of ammonia is a white or pinkish-coloured crystalline mass. It may be readily applied in the form in which it is sold by the gas-companies, and other manufacturers of the article. It is also occasionally added to other fertilizers, in order to increase the percentage of nitrogen.