Fish Oils.
—These are obtained by rendering from all parts of a fish where fat exists. The herring, sardine, salmon, and the menhaden are the fish which are chiefly used for getting oil of this kind. The fish oils have very much improved in quality since the steamer has taken the place of the sail boat for gathering the fish. During the days of the sail boat the fish were often kept for ten days after seining before they were brought ashore. The decomposition which took place would naturally affect the oil. At the present day the steamers fishing close to the shores deliver their products much more frequently, often the same day they are caught, and thus a better quality of oil is produced. In this country menhaden is the chief fish used for obtaining oil. The scientific name of menhaden is Brevoortia tyrannus. These fish appear in enormous quantities around the Atlantic coast from May until November. It is estimated that nearly one-half million tons have been taken of these fish during a season. Menhaden oil is rarely if ever used for edible purposes. It is used principally in the leather trade and sometimes in the adulteration of cod liver oil made in Newfoundland.
Sardine Oil.
—Sardine oil is principally prepared in Japan from the Japan sardine (Clupea sardinus). It is not used to any extent for edible purposes. It is also prepared to some extent in the boiling of sardines in France preparatory to packing in oil.
Salmon Oil.
—This oil is obtained in large quantities on the Pacific coast. It is one of the fish oils which has an agreeable odor and taste and, therefore, can be used for edible purposes. It has a specific gravity at 15 degrees of about .926 and its iodin number is about 160.
Cod Liver Oil.
—The most important of all the animal oils for food purposes is the oil which is obtained from the liver of the cod (Gadus callarias). Cod liver oil is valuable for food purposes not on account of its odor and taste, which are usually quite disagreeable, but by reason of the specific effect which it is often said to exercise in cases of emaciation and general disorder of the functional activities of the body. It is a food or medicine, whichever it may be best called, which is highly prized in tuberculosis and similar diseases. The oil is chiefly prepared in the Loffoden Islands. Different classes of oil are prepared which are differentiated chiefly by their color, the lighter the color the higher the quality of the oil. The chemical composition of cod liver oil is extremely complex, many different kinds of substances having been found in it by various authorities. The probability is that many of these supposed substances are only mixtures of others. Yet it cannot be denied that the number of chemical compounds occurring in cod liver oil is very much greater than that which occurs in ordinary oils. Both the medicinal and food values of the oil are often attributed to these bodies which occur in minute quantities.
Properties.
—Cod liver oil at 15 degrees has a specific gravity of .922. Its iodin number varies very greatly but is always high, ranging from 150 to 180. Its refractive index is also very high, namely 1.47.