Menhaden-oil, Straits or Bank Oil.—A fish eagerly sought for its oil on the Atlantic coast of America is the " menhaden " or " porgie " (Alosa [Brevoordia] Menhaden), a member of the herring family, about 8-14 in. long. The fishery is carried on all along the coast from Maine to Maryland. The fish leave the Gulf Stream and strike the coast of New Jersey in April, reaching the coast of Maine in May-June, and remaining till October-November. They migrate in enormous schools, and are caught in seines, carried by the fastest and smartest yachts. Very few of the fish are sent to table ; nearly all are boiled down for their oil. This is performed in the following manner. The fish are shot into receiving-tanks situated outside the building ; thence a sliding door opens into the boiling-tanks, which are long, watertight, uncovered boxes, of varying capacity, provided with a coil of perforated pipe for the admission of steam, and a plug-hole for the exit of the liquid after boiling. Some water is put into the tanks ready for the fish, and as soon as the latter have been introduced, steam is turned on, and the whole mass is boiled for 20-40 minutes. When the cooking is completed, the liquor, containing a portion of the oil of the fish, is drawn off into settling-tanks, for the recovery of the oil. The " pomace " or cooked fish is raked into " curbs," perforated cylinders fitted with hinged bottoms, and these, when full, are placed under hydraulic presses. Pressure is applied so long as water and oil continue to escape from the mass. The remaining solid matters, called "scrap," are treated for the preparation of a fertilizing compost (see Manures, p. 1257). The oil and water pass by gutters into settling-tanks, where the oil soon rises to the surface, and is skimmed off, or allowed to escape over a separating partition.
The oil is still crude, and requires clarifying and bleaching before it becomes a saleable commodity. This is effected in several ways. It is first boiled, to free it completely from water. It is purified from solid matters by running it into filter-bags suspended over casks, and then subjecting it to pressure in bags, the oil escaping while the sediment remains in the bags. This ' refuse, termed " foots," is bleached, and used for soap-making. The oil thus refined is termed "straits," and is ready for barrelling. " Bank " oil is an inferior grade. Bleaching is sometimes performed by exposure to the sun in shallow tanks, having glass covers to exclude dust when a superior quality is desired. The yield of oil is at its maximum in September, when a barrel (250) of fish gives about 4/ gal. of oil. The average product of 1000 fish is 13-14 gal. of oil. The total catch in 1878, an average year, gave 80,000 barrels of oil, 23,815 of which (644,762 gal.) were exported under the denomination of " fish-oil," and 45,000 were locally consumed. The exports in 1879 were 613,663 gal. Its principal application in America is for tanning and currying purposes. In France, it is largely employed as a substitute for cod-liver-oil, costing at Havre only about 45 fr. a 100 kilo., while the latter fetches 50-53 fr. In this country, it is said to be often passed off as olive-oil, and that considerable quantities of it arc mixed with linseed-oil for painters' use. The rapidity with which it oxidizes, and its good body, render it not unsuitable as a vehicle for paint ; the same causes make it inadmissible for lubricating.
Neats'-foot-oil (Fe., Huile de pieds de bceuf).—From " ox-feet," the feet and hocks of neat cattle cut off about 18 in. above the hoof, is obtained a valuable oil, known as "neats'-foot." Its preparation, which is usually performed by tripe-dressers, is as follows. The " feet " as received are denuded of akin, and slit up longitudinally, by a knife passed between the sections of the hoof and continued between the long bones. Near the hoof, is a small mass of soft fat, which is scooped out with the knife, and set aside for the preparation of the best quality of oil. The hoofs are washed
in cold water, and then boiled in open pans set in brickwork, and heated by a fire beneath. A certain quantity of oil is thus boiled out of them, and when skimmed off, forms an inferior grade of neats'-foot-oil. After about 3 hours' boiling, the tissues between the horny hoof and the last digit bone are sufficiently softened to allow of the latter being easily scooped out of the hoof with a knife. These " cores," consisting of bone, gelatinous matter, and fat, together with the small pieces of fat previously alluded to as being removed by the knife before boiling, are put into a separate pan of fresh water, and all boiled together for the extraction of the oil. This forma the best kind of neats'-foot-oil. It is reckoned that 10 " feet " will give about 1 qt. of oil. It is made in most large towns, and some quantities are shipped from the River Plate and the Falkland Islands. Phila delphia exported 1125 gal. in 1879.
This oil is usually yellowish or greenish in colour, but that from Buenos Ayres is often colour less. It is odourless when fresh, and of agreeable flavour. It is limpid, and remains so below a temperature of 0° (32° F.). Its density at 15° (59° F.) is On standing for a short time, a proportion of solid fat separates out, and may be filtered off. Its limpidity, which is intensified in the oil obtained from Buenos Ayres, causes it to be largely employed for lubricating, especially clocks and bearings exposed to the cold. It is very rarely found pure.
Niin-oil.—An insect belonging to the genus Coccus, and which has been named C. adipofera, affords an oil having considerable economic use in Central America. It feeds on the resinous sap of a species of Spondias, whose local cultivation is so easy that oven thick cuttings germinate quickly in almost any soil. The breeding of the insect is dependent simply upon the multiplication of this tree, which is already under extensive cultivation all over the tropics of continental and insular America. The female insects, which yield the oil, adhere to the trees by means of their beaks, existing in such large numbers that they frequently cover every portion of the plant. The oil is extracted from the insects by broiling or boiling them, and amounts to 26-28 per cent. of their weight. It is bright-yellow to yellowish-brown in colour, and possesses a peculiar odour. When recently melted, it is homogeneous, but soon becomes granular and lighter-coloured. Its melting point is about 49° (120° F.); when melted, it remains fluid at even 27°-29° (80°-85° F.). Cooled to —12° (10° F.), it becomes hard and brittle, like suet. At ordinary temperatures, it is thick and pasty, like lard, and its sp. gr. is about It is insoluble in alcohol, but freely soluble in hot and cold ether, forming a yellow oily liquid ; it is very soluble in turpentine, producing an oily liquid of special value for mixing delicate oil-colours ; it is also freely soluble in benzine and chloroform. It is a thorough drying oil, though its absorption of oxygen is slow, and is not hastened by boiling with oxide of lead. Its composition resembles that of ordinary animal fats. Its saponification is unusually difficult, and only effected after prolonged boiling with strong soda lye. When melted in a porcelain dish, and the resulting oil is exposed to a temperatere of 121° 177° (250°-350° F.) for an hour, or till a considerable part has evaporated, the residue assumes a tough, flexible, varnish-like condition, is no longer soluble in turpentine, and but little affected by heat and cold. This, ignited with turpentine, affords a thick, yellow gum or oleo-resin closely resembling a thick solution of indiarubber, possessing remarkable adhesiveness, and retaining the semi-fluid consistency for several days. When the turpentine solution of the oil is exposed in thin strata to the air for some days, it acquires the properties of a resinous varnish, almost equal to fine shellac varnish, very elastic and hard.