muffs, or stuffing boxes. This is a necessary precaution where hot blast is to be conducted a considerable distance. Elbows should be avoided as much as possible in blast pipes; and if necessitated to use them, the corner should be turned in as large a circle as possible. The loss of power of the blast, when suddenly turning round a corner, is very great. Acute angles, even those of 90°, are, if possible to be altogether avoided. The best location of blast pipes, where they are weak, and liable to break, or where the joints are not quite safe, is above ground. For well-constructed and properly cemented pipes, the best situation is below ground. But we ought to take the precaution of laying them in well-constructed, spacious channels, walled and paved with brick or stone, and covered with wood, stone, or cast iron plate. When laid in the ground and covered with earth, they are very liable to be injured, and seldom answer a good purpose. It is better to lay them above ground than to inclose them in an immovable position. Though corners of any kind are to be avoided in blast conductors, we must not, therefore, suppose that very straight pipes are the best form we can select. A gentle bend is advantageous, for it will tend to preserve the joints. Various plans of locating the blast pipes around a blast furnace have been adopted. In some instances, we see the pipes above the head; in others, walled in the pillars; and in others, again, below the bottom stone of the hearth. The latter plan is preferable; but, unless executed with due care, the result will be unfavorable. A blast pipe thus laid should be entirely free, that is, it should be at liberty to move exactly to that degree which the difference of temperature to which it is exposed inclines it. If this precaution is taken, we experience no trouble with it. An objection has been raised against laying the pipes in this manner, because, in some cases, hot cinder and hot iron have found access into the channels for the pipes. But such accidents cannot be deemed a valid objection. They They can be avoided by a judicious plan of laying the pipes, and by proper care in the management of the furnace.

a. The mouth-pieces of the blast pipes, called nozzles, are tapered sheet iron tubes, varying from one to four feet in length, according to locality, and the purpose which they serve. At one end, they are as wide as the conducting blast pipe, to which they are joined; at the other end, they are as wide as is considered necessary for the passage of the blast. These nozzles are frequently divided into two parts; one of which is permanent, and the other,

generally the shorter, movable. This facilitates a change in the dimensions of the nozzles. These conical pipes are either welded. or soldered with copper, for, as they are narrow, rivets will obstruct the blast, and make it exceedingly noisy. Where cold blast is used, the nozzles are generally connected with the main blast pipe by a leather bag. This bag is held to the pipes by means of an iron hoop. This hoop, of the form of a wristband, is tied to its place by a screw, which, by drawing the hoop close to the leather, and that to the pipe, makes an air-tight joint. Where hot blast is employed, leather cannot be put into the conducting pipe. In this case, everything must be metal. It frequently happens that the nozzles are to be temporarily removed; to facilitate this removal, and to avoid loss of time as much as possible, a joint is required. With cold blast, the motion of the nozzle from one place to another is frequently necessary, and more or less dip is required; for that purpose, the leather-bag connection is indispensable. With hot blast, this is not the case, and therefore movable nozzles are unnecessary.

The size of the nozzle is, under certain circumstances, a matter of great importance, and deserves more attention than it generally receives, particularly at charcoal blast furnaces, and charcoal forges. If the moving power of the blast machine is limited, then it is the opening of the nozzle which determines the pressure of the blast. As a given pressure is most advantageous, it is evident that the size of the nozzle must have considerable influence upon the smelting operations. The changing of nozzles must be conducted with reference to securing a permanent pressure, for this is isdispensable. The amount of blast may be increased or diminished. The diameter of the nozzle is of course subject to great variations. We employ nozzles of one inch diameter at charcoal forges; from one and a half inch to two and a half inches at charcoal furnaces; and from three to four inches diameter at coke and anthracite furnaces. Where other things are equal, the nozzles for hot blast should be larger than those for cold blast. The form or taper of the nozzle at the point is a matter of considerable consequence; the greater the taper, that is, the larger the angle of convergence towards the point, the more the blast spreads into the furnace. Its results are similar to those of a weaker blast. An application of this principle is made at the charcoal forge, and, in some places of the Old World, at the blast furnace, by employing two nozzles, which blow in such directions as to spread the blast in a greater degree among the hot coal.

Stronger blast may be thus applied to soft coal, in which case it is advantageous. The more cylindrical the form of the nozzle, the greater the degree in which the blast will be kept together in the furnace. This form improves the pressure of the blast. Similar results take place where only the extreme end of the nozzle is cylindrical to a length equal to the diameter of the opening. That is, a three inch nozzle requires a cylindrical nose three inches long to form a compact column of blast; and a two inch nozzle requires a nose two inches in length. Cylindrical nozzles are preferable for hard coal; tapered nozzles for soft coal, charcoal forges, and fineries. Long and narrow tubes occasion much friction ; therefore, it is advantageous to make the nozzles as short as possible. The current of blast is moulded at the very extreme end of the nozzle.

IX. Tuyeres.

Much doubt and uncertainty exist in relation to tuyeres, and therefore we shall make them the subject of special investigation. Before puddling was so generally introduced as at present, the shape and position of the tuyere at a blast furnace received considerable attention; but, since the quality of pig iron has been sought for with but little anxiety, the tuyere ceases to be of much importance. The chief purpose of the metallic tuyere is the preservation of the fire-proof hearthstones; the direction and form of the blast are of minor importance. This protection is accomplished, in some measure by making a coating of fire-clay in the tuyere hole, which is cut in the hearthstones. By this means, constant attendance, and repeated renewal with clay, will enable us to keep the tuyere narrow. No tuyere, whether of clay or metal, should ever be wider than the nozzle. Where one of the former kind exceeds the width of the nozzle, it burns away, and the hearth is exposed to destruction. The preservation of the original dimensions of the hearth is the main object which the manager of a furnace seeks to secure; and, as the clay tuyere does not effect this object, tuyeres made of copper or cast iron have been substituted in its place. These reach farther into the furnace than the clay tuyere, and, therefore, as it is decidedly of advantage that the blast should be driven as far as possible into the centre of the hearth, they are much preferable to the latter. Wrought iron tuyeres are liable to burn. The iron, in consequence of its purity, oxidizes, and forms with the clay around it a very fusible silicate, which is precipitated into the furnace. Gray is preferable to white cast iron, and also to wrought iron; the

carbon and impurities it contains protects it against oxidation and destruction. Copper is the best metal for tuyeres; it is a good conductor of heat, and is kept cool by the blast more easily than iron. Its silicates also are infusible. If copper oxidizes, and forms a silicate, the latter will protect it. The advantages derived from the copper tuyere have, in Europe, been acknowledged for more than a century; still, the charcoal furnaces in this country, at which cold blast is employed, are generally blown by clay tuyeres, the result of which is the waste of a great deal of coal, and the production of inferior iron. We do not recommend the application of the copper tuyere, for the water tuyere is preferable; but mention the above fact as a curiosity-as, in fact, one of those rare cases in which our citizens do not make the best use of the means at their disposal. The copper tuyere is protected against the heat of the furnace by the cold blast, which touches it, and cools it; for this reason, the tuyere should not be wider than the nozzle. In this point of view, we may regard the tuyere as a prolongation of the nozzle, in which case, of course, it is governed by the rules applicable to the latter. So long as pig iron is to be made for the charcoal forge, the desire to make white plate iron in the blast furnace will exist. It is very difficult, almost impossible, to keep a blast furnace constantly running upon a certain kind of iron; therefore, the difference which the quality of that in the furnace exhibits, is modified to a more or less general standard by means of the position of the tuyere, such as its direction and inclination. Very skillful 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 tuyere is yet in use; but where pig iron for puddling is made, or hot blast employed, the tuyere will not require such close attention. In this country, we can scarcely appreciate the niceties involved in adjusting the tuyere, not even at the forge fires; but this adjustment is unaccompanied with any practical convenience, for the trouble it requires is never compensated. The advantages which arise from a scrupulous attention to the tuyere are, at best, very small; and such attention would, under the conditions which exist in this country, especially the high price of labor, result in loss instead of gain.

a. At cold blast furnaces, in this country, clay or cast iron tuyeres, principally the former, are generally employed. Water tuyeres are in use at forges, fineries, hot blast, and at some cold blast furnaces. A common tuyere for the Catalan forge, the charcoal forge, finery, and charcoal blast furnaces, is made of boiler

plate; it is represented by Fig. 139. The top part is hollow, while the bottom part, which is generally flat, as shown at c, is solid. A

Section and view of a water tuyere with flat bottom.

water pipe of one-half inch bore conducts a current of cold water through the hollow top; this preserves the tuyere, and protects it against burning. The bottom is made flat, so as to serve as a support to the nozzle; we are thus enabled to move the latter to those places where it is most needed. At blast furnaces and fineries, this precaution is not of much use, for the nozzle remains at the place where it is fixed; but at forges it must be movable. Both of the water pipes are, in most cases, at the top; this arrangement can scarcely be considered so advantageous as that in which one pipe, or the entrance of the water, is nearer the bottom, and the other pipe, or the outflow, at the top.

b. Tuyeres for anthracite, coke, and most of the charcoal furnaces, are perfectly round, and made of boiler-plate; seldom of copper or cast iron. Fig. 140 shows a round water tuyere; this may be two inches wide at the narrowest point, as at charcoal furnaces, or from four to four and a half inches, as is the case at anthracite furnaces. The taper of the tuyere 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 tuyere is kept