The following is the method of manufacturing the oil for internal consumption. The apadicea are kept in a hot place for 3-4 days, and the nuts are then taken out. A small quantity (3-4 lb.) is made at a time. They are boiled in iron pots, then put into a wooden mortar, and pounded with wooden pestles. The pulpy mass is next mixed with tepid water with the hand. The chaff is first removed, and afterwards the stones. The oil remains mixed with the water, which is passed through a sieve (to remove the remaining chaff) into a pot placed on the fire, heated up to boiling point, and allowed to continue in that state whilst the oil floats up as a brigbt-red substance. The water at this stage is being continually stirred, and the oil is removed as it floats up until the whole is collected. The oil is now put into a pot and heated, to drive out any water that may remain.
It has been estimated that the yield of oil from this palm is at the rate of 7 cwt. an acre, or more than greater than the oil product from the olive in S. Europe. On some parts of the W. coast of Africa where the regular collection of the fruits is not practised, the trees grow so thickly, and afford such regular and rapid crops, that the ground becomes covered with a thick deposit of the fatty matter afforded by the fallen nuts.
The oil obtained from the pericarp, the palm-oil proper, has the consistence of butter, IL yellow colour, an odour resembling violets, and a mild flavour ; it easily becomes rancid, bleaches in the sunlight, saponifies readily with alkali, dissolves in all proportions of ether, and in alcohol at 0.818 sp. gr. Its industrial applications are for the manufacture of candles and soap (see Candles ; Soap); and the manufacture of tin-plate, in S. Wales and elsewhere. For this latter purpose, its non-drying qualities render it valuable as a preservative of the surfaces of the heated iron sheet from oxidation, until the moment of dipping into the bath of melted tin, the sheets being rapidly transferred to that from the hot oil bath, which consists almost entirely of palm-oil. The softest, purest, and most neutral oil is preferred for this purpose, and the kind known as " Lagos " is much used therefor. The exports of palm-oil from Lagos were 3,304,967 gal., value 239,133/., in 1877, and 1,570,638 gal., 139,094/., in 1878.
Until 10-12 years ago, palm-oil from certain parts of the African coast was usually mixed with the oil obtained in a very crude way from the kernel of the fruit (see Palm-nut-oil) ; as the kernels were somewhat burnt in the process of extraction, they communicated a peculiar smell to their oil, and that again to the palm-oil, which was known in the market as " coffee-oil," and, being difficult to bleach, and weaker in body, was considerably lower in price than good palm-oil. It is more usual
now, however, for the kernels to be sent to England to be treated.
Scarcely any oil that finds its way into commerce has a greater range of quality than palm-oil. The various kinds are well known by the names of the parts of the coast whence they are shipped. The oil used to be brought home by small vessels trading from London, Liverpool, and Bristol, which went out with empty casks, and lay some months along the coast, especially near the mouths of rivers, until they were filled up with oil. The great regularity with which steamers now call at many African ports, and the cheapness of freight, has materially altered the mode of conducting the trade. Casks are now left at the various depots, and instead of, as formerly, a 300-ton ship coming home laden with one or two classes of oil, steamers arrive regularly in Liverpool with car goes chiefly of palm-oil, made up at various ports of call, ranging perhaps from 8° N. and 13° W. (near Sierra Leone) to 10° S. and 12° E.
Along so great a range of coast, it is not a matter of surprise that there should be such variations in the quality of the oil, especially when, to differences in climate affecting the trees and their fruit are added differences in mode of preparation, &c. It is found, however, that the oil from any given port is tolerably uniform in quality. Thus, as explained before, Lagoa oil, which chiefly comes to London, is the most neutral (i.e. non-rancid) and the cleanest, the water and other impurities not exceeding 1-2 per cent. ; it is also nearly the softest. On the other hand, "Brass" oil is almost equally pure, but is the hardest of all the varieties, and contains the largest percentage of palmitin acid ; hence it usually commands the highest price for candle-making in the Liverpool market. " Cameroons " and " Windward " oils (which chiefly come to Bristol) occupy an intermediate position as regards hardness ; in the latter, impurities may amount to 5-6 per cent. " Saltpond" and "IVIonrovian " may be mentioned as instances of the most impure oils, 25 or even 30 per cent. being not an unusual amount of impurity. On this account, it has been proposed to sell palm-oil by analysis, guaranteed to contain — per cent. of clean oil, just as soda-ash is sold at, say, 55 per cent. soda. The presence of these impurities tends to partially decompose the oil, and render it harder, since the fatty acids are more solid than the neutral fat whence they are derived. Any determinations, therefore, of the melting- or solidifying-points of palm-oil are utterly misleading. Commercial palm-oil itself is a mixture of palmitine and oleine (the glycerides), and of palmitie and oleic acids, in very varying proportions, with the addition of uncertain quantities of water, vege table fibre, and sand.