such as its direction and inclination. Very skilful management is required, in many instances, to produce the desired effect. In some parts of Europe, where cold-blast iron for the forge is manufactured, the copper tuyère is yet in use; but where pig iron for puddling is made, or hot blast employed, such close attention is not necessary. In America, the niceties involved in adjusting the tuyère can scarcely be appreciated, not even at the forge fires; but this adjustment is unaccompanied with any practical convenience, as the trouble it requires is never compensated. The advantages which arise from a scrupulous attention are, at best, very small; and such attention would, under the conditions which exist in America, especially the high price of labour, result in loss instead of gain. At cold-blast furnaces, in America, clay or cast iron tuyères, principally the former, are consequently generally employed. Water tuyères are in use at forges, fineries, hot-blast, and at some cold-blast furnaces. A common one for the Catalan forge, the charcoal forge, finery, and charcoal blast-furnaces, is made of boiler plate. The top part is hollow, while the bottom part, which is generally flat, is solid. A water-pipe, of -inch bore, conducts a current of cold water through the hollow top: this preserves the tuyère, and protects it against burning. The bottom is made flat, so as to serve as a support to the nozzle; and thus the latter may be readily moved to those places where it is most needed. At blast-furnaces and fineries, this precaution is not of much use, as the nozzle remains at the place where it is fixed; but at forges it must be moveable. Both of the water-pipes are, in most cases, at the top; but this arrangement can scarcely be considered so advantageous as though one pipe, or the entrance of the water, were nearer the bottom, and the other pipe, or the outflow, at the top. Tuyères for anthracite, coke, and most of the charcoal furnaces, are perfectly round, and made of boiler plate; seldom of copper or cast iron. The tapering of them does not affect the furnace; and for all the evil this tapering occasions, it may be a perfect cylinder. In using hot blast, it makes no difference how the air is conducted into the furnace, provided the tuyère is kept open, and bright; which is all that is necessary. The nozzle is laid into the tuyère,-how far it reaches into it, is a matter of no consequence, and the space between them filled up with clay. At a cold-blast furnace, it requires some attention not to push the nozzle too far in, or to draw it too far back. The water-pipes are of lead, 4-inch, seldom 1-inch bore; one on the lower, and the other on the top part of the brim. The lower pipe conducts the water to the tuyère, and the upper one from it. The former is, in many cases, pushed as far as possible into its interior, to bring the cold water into the furnace; and the water is thus applied where the heat is greatest. A constant, uninterrupted supply is necessary to prevent the melting of the tuyère. The water must be pure; else it will leave a sediment in it which is sure to cause its destruction. There must, also, be a sufficient supply of cold water if the formation of steam is going on in the interior of the tuyère, the latter is sure to be burned. Copper and brass last longer than iron; but if iron tuyères are well made, and soldered with copper, and if there is no lack of water, they may last a long time. Where there is a deficiency of water, or where there are sediments in the interior of a tuyère, a few hours' heat will destroy it. If it be found that they do not wear well, attention must be directed to the water; and if nothing appears wrong, the application of larger pipes, or higher hydrostatic pressure, will then remedy the evil. Water tuyères are generally from 10 to 20 inches long; those that are too short are liable to be burnt, by the fire working around them, because there is not sufficient room to keep it closed up. Another disadvantage is, that their want of length prevents them from being pushed into the hearth; but length is necessary when the earth is burned out, and when the blast should be carried further into the interior. The external size is also a matter which requires attention in the construction. The total surface determines the amount of water which is necessary. The larger the surface, particularly the diameter, the greater the amount of water necessary, and of course the greater the danger of burning. A tuyère is seldom more than four inches in diameter inside; but the diameter outside is sometimes twelve, and even more inches. With such an increase of the diameter, however, the danger is augmented. Tuyères may be considered a prolongation of the nozzle or the blastpipe, and disconnected from it merely for the sake of preservation, and of more convenient access to the interior of the furnace. Those for cold blast should taper more than those for hot blast, because the former clinker in a greater degree, and require cleaning more frequently than the latter. The more acute the angle of the tuyère, the colder it works; and the more tapered it is, the hotter it works. These observations are of practical importance. In most cases the blast is required as far in the interior of the furnace as possible, because fuel is thus saved, better iron produced, and the hearth protected. There is some difficulty in giving cold-blast tuyères a slight taper, because they should be very wide outside; but this difficulty can be overcome by making their interiors more curved. If the extreme end, as far back as the diameter of the mouth, is cylindrical, the same purpose is accomplished as though the whole were cylindrical. If too much tapered, which is shown by its working too hot, the evil is diminished, in some measure, by pushing the nozzle further into the furnace. This is but a temporary, not a radical remedy; and a tuyère of a proper form must be substituted. If it works too cold, that is, sets on too much cold cinder, the only resource is scrupulously to keep it clean, and to replace it as soon as possible by one more tapered, or with a more obtuse cone. From these considerations, it is evident that different kinds of ore require a tuyère of different taper; but for the exact degree of this taper no general rule can be given. Experience must, in this instance, be the only guide. This will appear more evident on taking into consideration the kind of fuel and the pressure of the blast required. Calcareous ore, as well as the pig iron made from it, works naturally hot at the tuyère; consequently, those more acute are employed, and serve to drive the blast far into the furnace, by which means they are kept cool. This result can be effected by a water tuyère. Clay ores, which work naturally cold, work better with one that is tapered. These considerations, which have a special bearing upon the working of furnaces and forges, are entirely of a practical nature; and for this reason the management of the furnace or forge is accompanied with such different results. It is evident that the modification of a tuyère cannot, at times, be so quickly accomplished as may be desired: months, and even years, are often consumed, before the required form can be accurately determined; in many cases, this form is never arrived at. The shape is therefore a matter which, at blast-furnaces, generally depends on the decision of the keeper or founder; and as those formed of clay may be altered very conveniently, this may be assigned as one of the reasons why so many of that kind are in use. The whole matter, however, is divested of its mystery when it is found that an obtuse tuyère tends to work warm, while one more acute produces an opposite effect, and is more advantageous as respects both the quality and quantity of work; but it is more difficult to manage. The form of the nozzle, as well as that of a metal tuyère, is permanent; and as the advantage of either shape can be arrived at, in a more or less perfect manner, by pushing in or drawing back the nozzle, no solid objection exists against those formed of metal. Some difference should be made between the form of the nozzle and that of the tuyère. An obtuse nozzle should work with the latter more acute; a slightly tapered nozzle, with one greatly tapered. The latter form is generally preferred, on account of the facility of cleaning. In applying hot blast, the form of the tuyère and the nozzle is a matter of indifference; but in their construction it is found desirable to adopt the rules here suggested. The advantages of hot blast are sometimes doubtful; and it is therefore better to unite, by means of perfect forms of apparatus, all the advantages derivable from the cold blast, and thus to regain what is lost in quantity by its employment. In forge fires there are generally but one tuyère and two nozzles. At refinery fires the tuyères are often all on one side; at other places on opposite sides. All these differences are the result of local causes, originating in the form of the apparatus, the quality of the iron and fuel, the pressure of the blast, and the qualification of the workmen. Their number and their position in the blast-furnace deserve attention. In using cold blast, few should be employed, and in using hot blast as many as possible. Cold-blast tuyères are naturally troublesome; they are apt to become black, and require constant attention, as well in moving the nozzle as in patching them with clay; they also tend to produce white iron, and they cool the lower parts of the hearth. For these reasons their number should be reduced as much as possible, as the hot-blast tuyère works very hot, occasions but little trouble, is much inclined to produce gray iron, and tends to reduce silex, and consequently to produce a poor quality of iron. Therefore, the use of as many hot-blast tuyeres as can be conveniently employed is recommended. The position of tuyères is most favourable when placed on both sides of the hearth. The timp is that part of the hearth which is first burnt out; and if the tuyére is in the back part of the hearth, the distance from it to the opposite timp is unnecessarily increased. Tying, in mining, the term for washing ores Tympan of an arch, a triangular space or table in the corners or sides of an arch, usually hollowed, and enriched with branches of laurel, olive, oak, &c., and sometimes with emblematical figures Tympanum, the triangular panel of the fastigium of any building, comprehended between its corona and that of the entablature: the panels of a framed door were called tympana by the Romans Typhoon is a name frequently applied to a tropical storm: it is also given to the hot winds which occasionally blow with great violence in Africa, Syria, Arabia, and Persia; and which are felt, though rarely and with much-diminished force, in the southern parts of Italy and Spain. The sirocco of Egypt and the coasts of the Mediterranean, the simoom of Arabia, and the harmattan of the coast of Guinea, are understood to be so many desig nations of the typhoon; all of them being supposed to originate in the same cause, with modifications depending merely on the nature of the particles exhaled from the ground in the different countries. They are also said to cause water-spouts at sea. ULT ULTRAMARINE, Lazuline, or Azure, is prepared from the lapis lazuli, a precious stone found principally in Persia and Siberia. It is the most celebrated of all modern pigments, and, from its name and attributes, is probably the same as the no less celebrated Armenian blue, or cyanus of the ancients. Of the latter, Theophrastus informs us that the honour of inventing its factitious preparation (by perhaps a very singular chemico-mechanical process still used for ultramarine) was ascribed in the Egyptian annals to one of their kings; and it was so highly prized, that the Phoenicians paid their tribute in it, and it was given in presents to princes: hence it was a common practice, in those times, to counterfeit it. Ultramarine ashes (mineral gray) are the residue of lapis lazuli from which ultramarine has been extracted, and vary in colour from dull gray to blue. Although not equal in beauty, and inferior in strength of colour, to ultramarine, they are extremely useful pigments, affording grays much more pure and tender than such as are composed of black and white, or other blues, and better suited to the pearly tints of flesh, foliage, the grays of skies, the shadows of draperies, &c., in which the old masters were wont to employ them. Ultramarine broken with black and white, &c., produces the same effect, and is thus sometimes carried throughout the colouring of a picture. The brighter sorts of ul UNI tramarine ashes are more properly pale ultramarines, and of the class of blue; the inferior are called mineral gray. Umber, commonly called Raw Umber, is a natural ochre, abounding with oxide of manganese, said to have been first obtained from ancient Umbria, now Spoleto, in Italy. It is found also in England, and in most parts of the world; but that which is brought from Cyprus, under the name of Turkish umber, is the best. It is of a brown citrine colour, semi-opaque, has all the properties of good ochre, is perfectly durable both in water and oil, and one of the best drying colours we possess: it injures no other good pigment with which it may be mixed. Undecagon, a polygon of eleven sides Undercroft, a subterraneous apartment or crypt Underlay. When a vein in a mine hides or inclines from a perpendicular line, it is said to underlay Underlay shaft, a shaft sunk on the course of a lode Underlayer, in mining, a perpendi cular shaft sunk to cut the lode at any required depth Undershot wheel, in hydraulics, a wheel with a number of flat boards, which receive the impulse of the water conveyed to the lowest part of the wheel by an inclined canal Uniform motion. The velocity of a moving body is said to be uniform when the body passes over equal spaces in equal times Union screws or joints, in locomotive engines, the brass unions for connecting the elastic bore-pipe of the tender to the feed-pipe of the engine; smaller ones also connect the tender steam-pipe with the feed-pipe and with the boiler. The feed-pipe is likewise attached to the lower end of the pump by a large union screw. Unit of work. The measure of any amount of work is the work done where a pressure of 1 tb. is exerted through 1 foot, the pressure acting in the direction in which the space is described. If, instead of 1 tb. being moved through 1 foot, it be moved through 2 feet, it is clear that the work is doubled, or that two units of work have been done. The difference between the aggregate work done upon a machine during any time by those forces which tend to accelerate the motion, and the aggregate work, during the same time, of those which tend to retard the motion, is equal to the aggregate number of units of work accumulated in the moving parts of the machine during that time, if the former aggregate exceed the latter, and lost by them during that time, if the former aggregate fall short of the latter. In reference to the unit of time, the unit of mechanical power has been assumed to be 1 lb. raised 1 ft. high, and 1 minute as the unit of time; the unit of work will therefore be represented by 1 tb. raised 1 foot high in 1 minute. Now, it is assumed that a horse is capable of doing 33,000 such units of work, i. e. that he is capable of raising 33,000 lbs. 1 foot high in a minute, or 1 b. 33,000 feet high; and this is called a horse's power, and is the unit of work in reference to the unit of time commonly used in this country. Universal chuck, a circular plate to screw on the mandril of a lathe, and hold a nut or any small piece of metal to be bored in the plate are two or more radial slots, fitted by the jaws or pieces which project from the face of the chuck, moved by screws towards the centre, and tightened upon the nut Unmoor, in navigation, to reduce a ship to the state of riding by a single anchor and cable Unship, to remove any thing out of a ship Urn, an ancient utensil, used for a variety of purposes; sometimes as the receptacle of lots or for votes at the public election of magistrates; but its greatest and most frequent use was as a receptacle for the ashes of the dead after their bodies were burnt. These urns were sometimes kept in houses, and also put under tombstones, or within vaults or graves. Urns and similar Ivessels have been found in the burial-places of the ancient Britons. In modern times, the urn is an utensil of domestic use. VAC VACUUM, a vacuity or space unoccupied by matter; in pneumatics, the vacuum caused by an air-pump, which is a degree of rarefaction sufficient to suspend the ordinary effects of the atmosphere. Vacuum-pump, a pump connected to the boiler of a marine engine, for charging the boiler with water from the sea by discharging the air, VAL causing the water to rise within the boiler, from the pressure of the atmosphere without: by this means much labour and time are saved, which would otherwise be expended in lifting the vats Vair, a term in heraldry, being a fur composed of four distinct colours; argent, gules, or, and sable Valve, in hydraulics, &c., a lid con |