OIDIUM. (See Fungus.) OIL. The oils consist principally of carbon and hydrogen, they, however, have a great affinity for oxygen, and if exposed to the air soon absorb oxygen and thus become rancid, since besides oleine they contain more or less of other matter. Hence, the reason why fats so soon become putrid, so oils when oxydized either become rancid or are converted into resins. The fluid fats, oils of vegetables and animals, agree very closely as to their structure, as the following table will show, the constituents being those of a well known vegetable and an animal oil: Oils are divided into expressed or fixed oils, which are also subdivided into drying oils and common oils, and into distilled or essential oils. The common fat oils are like almond and olive, bland, preserving their flavor for a time, but at length becoming rancid; palm oil is solid. The drying oils are like linseed, hemp seed, nut oil; they attract oxygen readily from the air, evolving heat, and become solid. The essential oils impart to flowers and aromatic bodies their odor; they are very volatile, and are obtained by distilling the leaves or flowers with water. All vegetables contain a proportion of oil of some of these varieties, which may be obtained by digesting them in ether and alcohol; it is, however, fre quently below one per cent., while in other cases, as the nut, it is more than sixty per cent. In provender, the fattening quality is closely related to the percentage of common oil. The following table shows the per cent. : M. Payen found that the oil was everywhere present in the seeds of gramineous plants. The embryo contains much, the husk less, the fari naceous portion still less; but maize and oil-cake contain about nine per cent., whence the univer sally admitted superior fattening power of these two articles, so often practically proved. The plants principally cultivated for oil, are the olive, linseed, castor, bean, rape, bene-plant, pea-nut, sunflower, etc. Corn is also worked for its oil to some extent. The principal animal oils, are procured from the fat of swine, the whale, the 'cod, and other fish, also from seals and other marine animals. The residue, both fish and animals, after the oil is expressed, makes a most valuable manure, and the residue of many of the oil bearing seeds are valuable for fattening animals, as that of linseed, the pea-nut, while the residue of all are valuable as manure: When the cotton seed of the South comes generally to be used in this way, it will add greatly to the productiveness of the soil. Wax is a substance nearly allied to the oil producing fats. In fats, oils, and wax, from various countries, now in the Museum of the Depart ment of Agriculture at Washington, we find the following, which inclAde a number of essential oils: There are about half a dozen samples of Vegetable tallow and wax in this series. One
specimen of the. last named, the product of Myrica jalapensis, is received from Mexico. The vegetable wax of China and Japan is pro duced from the fruit of several trees belonging to the gdnus Rhus. The most important of these is Rhus suecedanea, and is grown exten sively. Rhus wnicifera, the lacquer tree, also . yields a wax, differing only in a slight degree from that of the wax-tree mentioned above. Rhus sylvestris, or the wild wax-tree is also worthy of mention. Vegetable tallow is pro duced in Japan from the annamomum peel?) lieu latum. Other specimens of vegetable tallow and wax are from the valley of the Amazon. The oils are quite numerous, and, where it has been possible to do so, the vegetable from whence derived are shown with them. Linseed and the more common oils have been received from various countries. The Russian collections included oils of anise, mustard, hempseed, wal nuts, sunflower, wild rape, camline seed and poppy, with a few specimens of the refuse or oil cake. Oils of Japan are represented by rape-seed oil, which is used for illuminating purposes, together with fish oil in Japanese households. The South American collection is quite interesting, and includes gingelly oil, (Sesamum iadicuni), cocos oil, from the cocos palm, secua oil, (from a cucurbitaceous plant), seje oil, from another species of palm, crab oil, from Carapa guianensis, ground-nut oil, castor oil, etc. Linseed, ricinus, and cotton-seed oils are shown from our own country,the last named in connection with its principal manufacture, that of soap, a full series of which is shown. A valuable collection of essential oils was pur ch.ised for exhibition at Philadelphia, and these have since been added to the museum collections. Among them may be mentioned oils of hemlock, wintergreen, wormwood, golden rod, pepper mint, spearmint, sassafras, pennyroyal, berga mot, cedar, oil of neroli, etc., the last named from flowers of Citrus aurantiacura, oil of sweet birch, (bark of Betula kaki), and oil from roots and stems of several species of Spiraa are shown. Among the animal products in this subsection are many specimens of beeswax, both native and foreign. A few animal-fats are also shown from South America; candles and soaps are also included in this group, limited collec tions of which were received from various localities. The mineral products are represented by series of coal-oils and petroleum, principally from our own country. Specimens of raw and crude paraffin are also exhibited, with some of the products of petroleum, as benzine, naphtha, etc. In this connection may be briefly men tioned a number of specimens of water-p•oof goods, canvas, leather, wood, etc., rendered so by parafline in solution. They are impervious to water while freely admitting air.