"scrap" is a much better fertilizer than the whole fish; for the undesirable element—the oil, which "clogged the earth and made it unfit for tillage"—has been removed, and the "scrap" is left, containing plant food in proportions far exceeding those of any known natural fertilizer.
The process of extracting the oil from the menhaden is very simple. When the fish is delivered at the factory it is immediately placed in large iron tanks, containing about a foot deep of water. Heat is then applied until the mass begins to simmer, when the heat is turned off. In this way the fish is thoroughly steamed, and the oil cells are more or less separated from the flesh, so that the oil can be readily and thoroughly released in the presses. Often, when the fish is rich in oil, a considerable quantity exudes during the steaming process. This is drawn off from the top of the simmering mass and runs in troughs to the oil tank.
After the steaming, the fish is placed in "curbs" (circular vessels having perforated bottoms) and rolled to the oil presses. Here the oil is released by hydraulic pressure, and the remainder is simply the nitrogenous part of the fish, which is called "scrap."
Fig. 3.—Steaming the Fish.
In the factories of the United States Menhaden Oil and Guano Association the oil is not rectified; it is expressed in the simple manner that I have explained, and then shipped to the different oil merchants and refineries of the United States and Europe.
The preparation of the scrap, or fish guano, is also very simple. After the oil is released, the solid matter is taken to the drying boards—a large field covered with closely fitting grooved and tongued flooring—upon which it is spread to dry. At Tiverton