Malden Island guano, as well as that from lowland and Starbuck Islands, all of the same archipelago, have been principally used in Germany, for the preparation of high-class super phosphates. The first-named contains nearly per cent. of nitrogen, besides tribasic phosphate of lime, about 74 per cent. ; carbonate of lime, 14; ferric oxide, 1.
The following is a comparative statement of the percentages of phosphoric acid in the various natural phosphates and in the superphosphates made from them :— Bonc-ash.—Bone-ash is another useful product, containing 60-80 per cent. of phosphates. It con sists of calcined bones, contaminated with more or less of foreign substances. Their nitrogen is driven off by the calcining, and is generally wasted. Bone-ash is imported mostly from S. America, also from the Baltic and Black Sea ports. It is rarely or never applied in its imported state, but is generally ground in mills, such as are used for reducing mioeral phosphates, described further on. In a finely comminuted state, it is employed in producing the better class superphosphates, or "bone-manures." Shoddy.—Woollen refuse and hair, generally known in the market as "shoddy," are essentially nitrogenous manures. Pure dry wool or hair contains about 17 per cent. of nitrogen, but the com mercial article commonly varies between 6 and 8 per cent. When applied in a crude form, it decomposes very slowly, and its benefit is observed for several seasons. Treatment with sulphuric acid hastens its absorption ; and it is often employed in the manufacture of other manures, solely as a source of nitrogen.
Animal Cliarcoal.—This is a phosphatic material, consisting of the ash produced by burning bones in close vessels (see p. 453). It is used in sugar-refineries, and other works, for purifying purposes, and when no longer efficacious in this respect, it finds a market with manure-manufac turers. The amount of phosphates contained in it may vary from 50 to more than 80 per cent., according to the purpose for which it has been employed. Before being used as a manure, -its phosphates are always rendered soluble by treatment with sulphuric acid ; generally it forms only an ingredient of superphosphates.
Sugar-scum.—The term " sugar-scum " is applied to a compound obtained from sugar-refineries, containing not only the solid impurities of raw sugar, but also occasionally the coagulable consti tuents of blood used in the refining process, as well as bone-char, when the char-dust is utilized by mixing it with the solution of sugar in the " blow-up " pan (see Sugar. Analyses of a series of sugar-scums in actual use by manure-manufacturers reveal great variety of composition :—(1) Phos phate of lime, 11.75 per cent. ; ammonia, 1.18. (2) Phosphates, 26.00 ; ammonia, 3.4. (3)
Phosphate of lime, (4) Phosphate of lime, 3.11; nitrogen, = ammonia, (equal, in dry scum, to nitrogen, 2.88 = ammonia, 3.49). (5) Phosphate of lime, ; nitrogen, 0.98 = ammonia, 1.19. (6) Phosphoric acid, ; nitrogen, 1.36 = ammonia, 1.65 (equal, in dry scum, to nitrogen, 1.83 = ammonia, 2.22). (7) An analysis of the dried contents of the filter-bags at a sugar-refinery where no blood is used gave :—Moisture, organic matter, 41.6 (containing 17•8 sugar, and nitrogen) ; ferric oxide, 0.72 ; alumina, none ; phosphoric acid, ; lime, 22.5; magnesia, 1.83 ; sulphuric acid, 6.82 ; chlorine, none ; carbonic acid, 11.3 ; insoluble residue, 7-76 ; alkalies and loss, 1.94. Comparative analyses of samples taken respectively from (a) the filter-bags of a refinery where no blood is used, and from (b) those of another (belonging to the same firm) where several pails of blood are added to each charge of the " blow-up " pans, gave the following results :—Moisture. a 48.58, b 46.95 ; organic matters, a 20.82, b mineral matters, a I) 23.50. The mineral matter contained—phosphoric acid, a 4.03, b 2.24 ; and the organic matter— nitrogen, a'0.48, I 019 = ammonia, a 0.59, b 1.09. Comparing these results with those of analyses (4), (6), and (7) above, the quantity of nitrogen appears very much lower. The inference to be drawn from this is that scum from refineries where neither blood nor char-dust is used would probably be of little value to the manure manufacturer. That procured from one sugar-works is said to contain 18-20 per cent. of phosphate of lime. The exhausted bone-black from sugar-refineries contains about 58 per cent. of triphosphate of lime and magnesia, and 8.8 of carbonate of lime. • Scutch.—The term " scutch " is applied to the refuse from glue-works. It is usually treated with heat and sulphuric acid, to separate any fat it may contain, before being used for the manufacture of manure. Sometimes this is conducted in open or partially closed vessels by the aid of free steam ; as the fat separates, it is skimmed off, and when all of it is removed, the residue is run off into a tray, to cool snd consolidate. In some works, it is run into trenches dug in the earth, and after several mouths, is dug out, and dried in kilns or brick flues ; at others, it is collected in a heap, and left to dry by spontaneous heating.