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they find out some convenient retreat, and change to the chrysalis; and in about six or seven weeks the fly appears “The perfect fly but ill sustains the changes of weather; and cold and moisture in any considerable degree, would probably be fatal to it. These flies never pursue the horse into the water. This aversion, I imagine, arises from the chillness of that element, which is probably felt more exquisitely by them, from the high temperature they had been exposed to during their larva state. The heat of the stomach of the horse is much greater than that of the warmest climate, being about 102 degrees of Fahrenheit, and in their fly state they are only exposed to 60, and from that to about 80 degrees. This change, if suddenly applied, would in all probability be fatal to them; but they are prepared for it, by suffering its first effects in the quiescent and less sensible state of a chrysalis. I have often seen this fly, during the night time and in cold weather, fold itself up with the head and tail nearly in contact, and lying apparently in a torpid state through the middle of the summer.” O. ovis: wings pellucid, punctured at the base; abdomen variegated with white and black. It deposits its #. on the inner margin of the nostrils of sheep, occasioning them to shake their heads violently, and hide their noses in the dust or gravel. The larva crawl up into the frontal sinuses, and when full fed are again discharged through the nostrils. See Pl. III. Entomology, fig. 7 and 8. OFFENCE, is any act committed against any law. Offences are either capital, or not capital. Capital offences are those for which the offender loses his life; not capital, where the offender may lose his lands and goods, be fined, or suffer corporal punishment, or both, but which are not subject to the loss of life. OFFERINGS. Oblations and offerings partake of the nature of tithes; and all persons, who by law ought to pay their offerings, shall yearly pay to the parson, vicar, proprietary, or their deputies, or farmers of the parishes where they dwell, at such four offering days, as heretofore within the space of four years last past hath been accustomed, and in default thereof shall pay for the said offerings at Easter following. OFFICE, is that function, by virtue of which a person has some employment in the affairs of another. An office is a right to exercise any public or private employment, and to take the fees and emolu

ments belonging to it, whether public, as those of magistrates, or private, as of bailiffs, receivers, &c. The statute 5 and 6 Edward VI. c. 16. declares all securities given for the sale of offices unlawful. And if any person shall bargain, or sell, or take any reward, or promise of reward, for any office, or the deputation of any office, concerning the revenue or the keeping of the king's castles, or the administration and execution of justice, unless it be such an office as had been usually granted by the jus. tices of the King's Bench, or Common Pleas, or by justices of assize, every such person shall not only forfeit his right to such office, or to the nomination thereof; but the person giving such reward, &c. shall be disabled to hold such office. But it has been decided, that where an office is within the statute, and the salary certain, if the principal make a deputy, reserving by bond a less sum out of the salary, it is good : or if the profits are uncertain, reserving a part, as half the profits, it is good; for the fees still be. long to the principal, in whose name they must be sued for. But where a person so appointed gives a bond to the principal to pay him a sum certain, without reference to the profits, this is void under the statute. To offer money to any officer of state, to procure the reversion of an office in the gift of the crown, is a misdemeanor at common law, and punishable by information; and even the attempt to induce him, under the influence of a bribe, is criminal, though never carried into exe. cution. An instance of which occurred under the administration of Mr. Addington, who prosecuted a tinman for offering a sum of money to him for a place in the Customs. Any contract to procure the nomination to an office, not within the statute 6 Edward VI. is defective, on the ground of public policy; and the money agreed to be given, is not recoverable. OFFICER, a person possessed of a post or office. The great officers of the crown, or state, are, the Lord High Steward, the Lord High Chancellor, the Lord High Treasurer, the Lord President of the Council, the Lord Privy Seal, the Lord Chamberlain, the Lord High Constable, the Earl Marshal: each of which see under its proper article. OFFICERs, commission, are those appointed by the King’s commission: such are all from the general to the cornet in

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clusive, who are thus denominated in contradistinction to warrant officers, who are appointed by the colonel’s or captain's warrant, as quarter-masters, sergeants, corporals, and even chaplains and surgeons. Officens, field, are such as command a whole regiment, as the colonel, lieutenant colonel, and major. Officers, general, are those whose command is not limited to a single com. pany, troop, or regiment; but extends to a body of forces, composed of several regiments : such are, the general, lieutenant-general, major-generals, and brigadiers. OFFICERs, staff, are such as, in the King’s presence, bear a white staff, or wand; and at other times, on their going abroad, have it carried before them by a footman, bare-headed: such are the Lord Steward, Lord Chamberlain, Lord Treasurer, &c. The white staff is taken for a commission, and at the king's death each of these officers breaks his staff over the hearse made for the king’s body, and by this means lays down his commission, and discharges all his inferior officers. OFFICERs, subaltern, are all who administer justice in the name of subjects: as those who act under the Earl Marshal, Admiral, &c. In the army the subaltern officers are, the lieutenants, cornets, ensigns, sergeants and corporals. OFFICIAL, by the ancient law, signifies him who is the minister of, or attendant upon, a magistrate. In the canon law, it is especially taken for him, to whom any bishop generally commits the charge of his spiritual jurisdiction; and in this sense there is one in every diocese called officialis principalis, whom the laws and statutes of this kingdom call chancellor. 32 Hen. VIII. 15. OFFING, or OFFIN, in the sea-language, that part of the sea a good distance from shore, where there is deep water, and no need of a pilot to conduct the ship: thus, if a ship from shore be seen sailing out to seaward, they say, she stands for the offing; and if a ship, having the shore near her, have another a good way without her, or towards the sea, they say that ship is in the offing. OFF-SETS, in gardening, are the young shoots that spring from the roots of plants; which being carefully separated, and planted in a proper soil, serve to propagate the species. Off-sets, in surveying, are perpendiculars let fall, and measuring from the sta

tionary lines to the hedge, fence, or extremity of an inclosure. OGEF, or O G., in architecture, a moulding, consisting of two members, the one concave, and the other convex; or, of a round and a hollow, like an S. OGIVE, in architecture, an arch, or branch of a Gothic vault; which, instead of being circular, passes diagonally from one angle to another, and forms a cross with the other arches. OIL. The general characters of oils are combustibility, insolubility in water, and fluidity. From the peculiar properties of different oils, they are naturally divided into two kinds; fixed or fat oils, and volatile or essential oils. The fixed, or fat oils, require a high temperature to raise them to the state of vapour, a temperature above that of boiling water; but the volatile, or essential oils, are volatilized at the temperature of boiling water, and even at a lower one. Both the volatile and fixed oils are obtained from plants, and sometimes from the same plant; but always from different parts of it. While the seeds yield fixed oil, the volatile oil is extracted from the bark or wood. One of the most distinguishing characteristics of the fixed oils is, that they exist only in one part of the vegetable, in the seeds. No trace of fixed oil can be detected in the roots, the stem, leaves, or flowers of those plants, whose seeds afford it in great abundance. The olive may seem an exception to this. The oil which it yields is extracted, not from the seeds, but from its covering. Among plants too, fixed oils are only found existing in those whose seeds have a peculiar structure. The seeds of plants have sometimes one lobe, in which case they are called “ monocotyledonous” plants; and sometimes they have two, when they are denominated “dicotyledonous.” The formation of fixed oil in plants is exclusively limited to the latter class. There is no instance of fixed oils being found in the seeds of plants which have only one lobe. Those seeds which yield the fixed oils contain also a considerable portion of mucilage, so that when such seeds are bruised and mixed with water, they form what is called an emulsion, which is a white fluid, containing a quantity of the oil of the seed mixed with the mucilage, Fixed oils are extracted from the seeds of a great number of plants. Those which yield it in greatest abundance are, the olive, thence called olive oil; the seeds of lint, and the kernels of almonds, called linseed, or almond oil. Fixed oils

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are also obtained from animals; such as train oil, as it is called, which is extracted from the fat or blubber of the whale. Fixed oil is obtained also in great abundance from the livers of animals, and is found to exist in the eggs of fowls. These different kinds offixed oils, although they possess many common properties, yet in others they are very different. Many of the vegetable oils have no smell, and scarcely any perceptible taste. The animal oils, on the contrary, are generally extremely nauseous and offensive. These differences are supposed to be owing to the mixture of extraneous bodies, or to certain chemical changes, which arise from the action of these bodies upon each other, or on the oil itself. As the fixed oils exist ready formed in the seeds of plants, they are generally obtained by “expression,” and hence they have been called “expressed oils.” This it done by reducing the seeds to a kind of pulp, or paste, which is enclosed in bags, and subjected by means of machinery, when it is obtained in the large way, to strong pressure, so that the oil flows out, and is easily collected. The oil which is obtained by this process, which has been called “cold drawn oil,” because it is procured without the application of heat, and merely by pressure, is the purest; but the quantity which seeds in general yield is comparatively small, and some seeds which contain a considerable portion of oil scarcely afford any when treated in this way. It therefore becomes necessary, for extracting the oil from seeds of the latter description, and to have it in greater abundance from all seeds, to employ heat, to facilitate the separation of the oil from the mucilage, or other matters with which it is combined. For this purpose heat is applied, either to the apparatus which is employ. ed in pressing out the oil, or the bruised seeds are exposed to the vapour of water, and sometimes they are boiled in the water itself: by which means those substances which are soluble in water are separated, and thus the oily part which adhered to these substances is disengaged. The oils which are obtained in this manner are very impure. They are mixed with mucilage, and other parts of the substances from which they have been extracted. Many of these matters separate from the oils when they are left at rest. They are sometimes mechanically purified by filtration through coarse cloths, by which means the grosser parts are separated. Different oils too, it is said, undergo different kinds of purifica

tion by different manufacturers, but these rocesses are kept secret. After they have remained at rest for some time, they are filtered and agitated with water, by which the parts that are soluble in this fluid are separated from the oil. Sometimes they are gently heated, for a shorter or longer time, according to the nature of the substances with which the oil is contaminated. Acids diluted with water are employed to separate the mucilage; lime and the alkalies are also used, to combine with an acid which holds this mucilage in solution, and thus to favour its precipitation. Alum, chalk, clay, and ashes, are also employed in the purification of oils. Fixed oils are generally liquid, but of a thick, viscid consistence, and in general they are lighter than water. The specific gravity varies from 0.91, which is that of olive oil, to 0.94, that of linseed oil. The boiling point of the fixed oils is not under the temperature of 600°. When exposed to cold they congeal, and even crystalize. There is, however, a considerable variety, in this respect among fixed oils: some become solid at the tem. perature of a few degrees above the freezing point of water: while others, on the contrary, require a degree of cold = 5°; and some remain fluid when exposed to the greatest cold. Those oils, it has been observed, which most readily ecome solid, such as olive oil, are least subject to change; while those which congeal with difficulty have a greater tendency to spoil and become rancid. When fixed oil is exposed to heat it does not evaporate, till it is raised to the temperature of boiling, or 600°; but when it is thus raised in vapour, its properties are changed. It is decomposed by the separation of some of its principles. The part that is volatilized has a greater proportion of hydrogen; charcoal is deposited, and water and sebacic acid are formed, while carbonated hydrogen gas is disengaged. When oil is exposed to the open air, and a burning body is brought in contact with it, it readily takes fire, and burns rapidly, with a yellowish white flame. It is on this conversion of oil into vapour, and the inflammation of this vapour, that the application of oil in lamps and candles depends. . The oil is gradually and in small quantities brought in contact with the burning part of the wick; it is converted into vapour, which is immediately inflamed, and continues to burn till new portions are supplied to undergo the same change, and thus keep up a constant and uniform light and heat. According to the analysis of olive oil by Lavoisier, it is composed of hydrogen and carbon, viz.

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Carbon . . . . . . 78.92 Hydrogen . . . . . 21.98 100.00

The fixed oils are insoluble in water. When it is necessary to combine them with this liquid, it is by means of mucilaginous substances, in which case the mixture is known under the name of emulbion; or with alkaline substances, when it is distinguished by the name of soap. Some of these oils become thick, opaque, white, granulated, and are analogous in appearance to tallow. Oils subject to this change are called fat oils; such, for instance, is olive oil, almond oil, and rapeseed oil. This change is more or less rapid in different circumstances. If a thin layer of oil be spread on the surface of the water, and exposed to the air, it takes place in a few days, and this effect is owing to the absorption of oxygen, which combines with the oils. But other oils, when they are exposed to the air, dry altogether, yet have the property of retaining their transparency. Oils which have this peculiar property are called drying oils. The oil of poppies, hemp-seed oil, and particularly linseed oil, are possessed of this property. The nature of the change which takes place in these drying oils is supposed to depend on the absorption of oxygen; and this oxygen combining with the hydrogen of the oil forms water. This opinion is supported by the practice which is followed to increase the drying property of linseed oil. It is usually boiled with litharge, before it is employed by painters. The litharge in this case is partly reduced to the metallic state, by being deprived of its oxygen, which is supposed to combine with the oil. Phosphorus combines with oils, with the assistance of heat. A small portion of the phosphorus is dissolved, which communicates a luminous property to the oils, so that when they are spread upon any surface they shine in the dark. Hence some twenty years ago a person exhibited in London, as the everlasting lamp of the ancients, a vessel containing phophorus immersed in oil.

The various purposes to which fixed oils are applied are too well known to require particular enumeration. They are employed in domestic economy, either as articles of food, and for this purpose are used alone, or in combination with other substances; or they are employed

for giving light, by being burnt in lamps. They are used in medicine, either on account of the properties which peculiar oils possess, or on account of the properties they communicate to other substances with which they are combined. In this state the use of oils is well known, in the form of unguents, plasters, and liniments. In the arts fixed oils are of the most extensive utility. They are employed in the fabrication of soaps, for mixing colours in painting, for some kinds of warmish, and for defending substances from the action of air and moisture. Volatile oils are distinguished from the fixed oils by their volatility, fragrance, and acrid taste. They are also known under the name of aromatic oils, from their odour; or essential oils, or simply essences, from being supposed to constitute the essence or the existence of the vegetable matters which furnish them. Volatile oils are not limited to particular parts of plants, but are found to exist in every part of the plant, excepting in the seed which furnishes the fixed oils. A great number of roots, which are generally distinguished by aromatic odour, and have more or less of an acrid taste, af. ford volatile oils. They are furnished also by many woods, such as those of the pine and fir tribe, and by many of those which are natives of warm climates. The leaves of a great number of plants be: longing to the Didynamia class also afford volatile oil, as well as many of the umbelliferous plants. It is obtained also from many flowers of vegetables, and also from the covering of many fruits, as the skin of oranges and lemons. It is likewise ohtained from a great number of seeds; but it is never found in the cotyledons or lobes themselves, but only in the external covering. The quantity of volatile oil which is obtained from vegetables varies, according to the age, the soil in which they grow, and the state of the plant. Some plants, while green, furnish it in greatest abundance, while others yiel most when they are dry. There are two processes by which volatile oil may be obtained. When it exists in plants in great abundance, and in vesicles in a fluid state, it may be separated by mechanica means. Thus, by simple expression, the volatile oils are extracted from many plants, as, for instance, from the fruit of the orange and the lemon. From the outer rind of these fruits, when they are fresh, the volatile oil is obtained in the liquid form; but in general the volatile oils of plants are neither so abundant, no do they exist in that state of fluidity, by which they can be procured by so simple a process. In most cases they are subjected to the process of distillation; and for this purpose they are macerated for some hours in water. They are then introduced into a still with the water; a moderate heat is applied, and continued till the fluid boil, when a great quantity of vapour of water, mixed with the volatile oil, passes over, and is received in proper vessels. The oil collects on the surface of the water, from which it may be easily separated. The water itself is of a milky colour, on account of a small quantity of oil suspended in it; and even after the water becomes transparent by the particles of the oil separating from it, and rising to the top, it is still loaded with the peculiar odour of the plant. The volatile oils are particularly distinguished by their fragrance, which varies in the cils extracted from different plants. The consistence of the volatile oils also varies considerably. Sometimes they are as fluid as water, which is the case with those oils obtained by expression. Some are thick and viscid, as those generally are which are extracted from woods, roots, barks, and fruits of the warmer regions. Some congeal, or assume a granulated solid consistence, at different temperatures. Of these last some are al. ways found to be in the concrete state. Several of the volatile oils are susceptible of crystallization, depositing in the remaining portion of the oil which continues liquid, transparent polyhedrons, more or less of a yellow colour, which are found to be pure oil. This last change is probably owing to an incipient oxydation; for it never takes place unless oils have been kept for some time. There is great variety of colour among volatile oils. Some indeed are nearly colourless, as the oil of turpentine; but in general they are of different shades of colour. Some are yellow, as the oil of lavender; some are of a reddish yellow or brown, as the oil "f cinnamon or of rhodium; some are lue, as the oil of chamomile; and some are green, as that of parsley. But the most prevailing colour among volatile oils is yellow or reddish. Wolatile oils have almost always an *rid, hot, and even burning taste. It * observed that the most acrid vegetable otters do not yield an oil possessed of this quality. The specific gravity of vo*tile oils is generally less than that of Water. Some volatile oils, however, as *: of sassafras and canella, have a Sater specific gravity. The specific WOL, o gravity p

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gravity of oils varies from 0.87 to 0.99, in those which are lighter than water; but those which are heavier are from 1.03 to 1,40. When volatile oils are exposed to the light, the colour becomes considerably deeper; they become thicker, and increase in specific gravity. When volatile oils are exposed to heat, they evaporate very readily. They are much more combustible than the fixed oils; and in burning give out, a great quantity of smoke, a very bright white flame, and a good deal of heat. They require a greater proportion of oxygen than the fixed oils, and yield a greater quantity of water. This arises from a greater proportion of hydrogen, and a smaller quantity of carbon, which they contain. The volatile oils are in some degree soluble in water. When they are agitated with this liquid they combine with it, and communicate a very strong odour, and a slightly acrid taste. Phosphorus and sulphur are soluble in volatile oils. With phosphorus the solution is luminous in the dark, is extremely fetid, and gives out by the force of heat phosphorated hydrogen gas. Some of these oils are employed in medicine. They are used also for the solution of those substances which are to be employed as varnishes; and many of them are used in perfumery. As many of the volatile oils are produced but in small quantity, they are consequently high priced. There is therefore some temptation to adulterate them with fixed oils, with cheaper volatile oils, or with other substances, to increase the quantity. It is therefore of some importance to be able to detect such frauds. When a volatile oil is adulterated with a fixed oil, there is a very easy test to discover it. Let a single drop of the oil that is suspected fall on clean paper, and expose it to a gentle heat. If the oil is pure, the whole will be evaporated, and no trace remain on the paper; but if it has been mixed with a fixed oil, a greasy spot remains behind. Volatile oils are frequently adulterated with oil of turpentine; but this can only be detected by its peculiar odour, which continues for a longer time than most of the other volatile oils. When they are adulterated with alcohol, it is easily detected by mixing a little of the oil with water, which immediately produces a milkiness, by the abstraction of the alcohol from the oil, and its combination with the water. There is another class of oils, known under the name of empyreumatic oils, which have different properties from those which F

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