The best quality of this guano may contain as much as 10 per cent of nitrogen, but as a rule it is nearer 8 per cent. A very considerable variation in the amount of phosphoric acid occurs for the reason above stated, the guano made from fish-scrap being naturally much richer in this ingredient than whole-fish guano. The phosphoric acid may be said to range from 4 to 15 per cent, and there is also a small quantity of potash present. Guano is also manufactured in Norway from the carcasses of whales. Such guano contains from 7-1/2 to 8-1/2 per cent of nitrogen, and about 13-1/2 per cent of phosphoric acid. In America fish-guano is manufactured to a considerable extent--one important source being the menhaddo, a coarse sort of herring. This fish is caught for the sake of its oil, which is extracted by boiling, the residue being manufactured, after pressing and drying, into guano. In this country the manufacture of fish-guano is carried out to a considerable and increasing extent. Formerly it was imported from Norway to a larger extent than is now the case, the present annual imports amounting only to 1000 or 2000 tons. The total annual production in the United Kingdom is probably 7000 or 8000 tons. _Value of "Fish-Guano."_ That fish-guano is a valuable manure there can be no doubt. What, however, impairs its value is the fact that, as a rule, it contains a certain amount of oil. The effect of this oil is to retard fermentation and decomposition when the guano is applied to the soil, and thus render its action slower than would otherwise be the case.