of value only to a certain extent. Hot blast has been applied to charcoal forges, and is still so applied; but experience clearly shows that it injures the quality of the iron manufactured. Hence, it offers no possible advantages, for what is gained in quantity is lost in quality. Charcoal forges are valuable, in our country, as a means of producing quality. If that object is compromised, which is surely the case where hot blast is employed, charcoal iron will be brought to a level with puddled iron. This would be the surest method of making charcoal forges unprofitable. In the Catalan forge, hot blast may be employed advantageously in the melting down of the ore or cinder; but in the breaking up or blooming, cold blast should be employed.

Hot air is of but little advantage in puddling and reheating furnaces, or sheet iron ovens, where bituminous fuel, such as wood, turf, or bituminous stone coal, is used. If we burn anthracite in these furnaces, we may realize a moderate gain by hot air, provided the air can be heated by waste heat. This remark may be particularly applied to the reheating furnace, where large piles of iron are to be reheated; for free oxygen is generally contained in the flame of this furnace even in the highest heat. This oxygen, in some measure, works destructively on the iron to be reheated. Its amount will be greater in an anthracite reheating furnace than in any other; still, it may be reduced by the employment of hot

air.

At the blast furnace, economy of fuel is an important object; not so much because fuel is valuable in itself, but because wages are high; the handling of fuel, as well as the keeping of a fire, requires labor. For these reasons, air is generally heated at the top of the furnace. Coke furnaces may be considered, with the exception of a few anthracite furnaces, the only ones at which the blast is heated by separate fuel, and where extra labor is required. The top flame of any blast furnace contains far more heat than any air apparatus requires. Apparatus which is not constructed on the principle of economizing fuel, is the most practical. The air stove should be so constructed as to secure durability and simplicity. The flame may be conducted directly from the top to the stove; or the gas may be tapped below the top, and conducted in pipes or channels to the stove, just as we choose; either method is good, and by either method we may obtain as much heat as we require. Where the steam which drives the blast machine is generated at the top of the furnace, as is generally the case, it is advis

able to place the air-heating stove at the end of the steam boilers; for there is sufficient heat left, after the flame has passed under the steam boilers, to heat the blast to any degree which may be considered profitable. What makes this arrangement, common at the anthracite furnaces, more profitable, is the fact that the gas, by the time it passes the steam boilers, is, in some measure, cooled, and not sufficiently hot to injure the air-pipes. This result frequently occurs where the apparatus is put directly to the trunnel-head.

The economical advantages arising from the application of hot blast, casting aside those cases in which cold blast will not work at all, are immense. The amount of fuel saved, in anthracite and coke furnaces, varies from thirty to sixty per cent. In addition to this, hot blast enables us to obtain nearly twice the quantity of iron within a given time that we should realize by cold blast. These advantages are far more striking with respect to anthracite coal than in relation to coke, or bituminous coal. By using hard charcoal, we can save twenty per cent. of fuel, and augment the product fifty per cent. From soft charcoal we shall derive but little benefit, at least where it it necessary to take the quality of iron into consideration.

CHAPTER VIII.

WASTE HEAT AND GAS.

WASTE heat is an article so abundant in iron manufactories that a profitable method of using it should be deemed an object of considerable importance. Its application, owing to various causes, has sometimes been attended with only partial success. This partial success is to be attributed, in many instances, to the fact that it has been applied at the wrong place, in which case, the nature of the heat required is not understood. If we consider the very limited capacity of iron for heat, and the high temperature at which the gases escape, the amount of heat wasted in iron works will prove to be immense. In a reheating furnace, for example, a small amount of the caloric generated would suffice to heat the iron to a welding heat; but a great deal of this heat is lost, because some time must elapse before the heat of the furnace can be imparted to the iron; besides, with the welding heat the flame escapes. The most successful method of saving fuel in iron manufactories is to save time; if we gain one-fourth of a given period of time, we save, in most cases, twenty-five per cent. of fuel. If we make six heats in a puddling furnace, instead of four, we save thirty-three per cent. If a reheating furnace of a given size can be made to produce eight tous of iron a day instead of four, nearly fifty per cent. of fuel will be saved. This is the true principle on which economy of fuel in iron manufacture is based. But, even when economy is carried to the furthest extent, we may imagine that the waste heat which is lost amounts to at least eighty or ninety per cent. of that generated. In employing waste heat, we are too apt to confound the quality with the quantity of heat. We see an immense amount of heat wasted; but we do not reflect that the temperature of this heat is very low, and that it is a want of intensity which makes its application very limited. We possess no means to raise this temperature; at least, there are few instances in which it can be

raised to such a degree as to make it useful in our manufacturing apparatus. Waste heat cannot be generally employed, on account of the chemical composition of the flame, or gases, which contain the heat. The waste flame of the furnace contains a greater or less amount of free oxygen, or, at least, a large amount of watery vapors, which is the same thing, for these vapors are decomposed when in contact with hot iron. An excess of free oxygen, and low temperature, are, in most cases, highly disadvantageous. For example, the waste heat of a reheating furnace would be of no more service than the flame from green wood. We can not use it in a puddling furnace, in which inferior pig iron is converted. In most cases, its employment would interfere with important operations, in which case a loss would be experienced which the gain in fuel could not repay.

I. Waste Heat.

a. The waste heat of mill furnaces may be advantageously employed to generate steam, and to propel rollers, hammers, squeezers, and blast machines. This is the case in the anthracite region generally, as well as in some of the rolling mills on the Ohio River. In some cases, the waste heat is conducted in flues under the steam boiler; in others, the steam boiler is laid on the top of the puddling or reheating furnace, and receives the heat from the flue of the furnace before it enters the stack. Where anthracite, which is not easily kindled, is burned, the waste heat, after it passes the steam boiler, may be employed in heating, to a limited degree, the alimentary air for the grate. This will have a beneficial effect, for the waste heat increases the temperature of the furnace, and occasions a direct saving of about ten per cent. of fuel; duly estimating both advantages, the saving will amount to at least twenty per cent. Heating of blooms, and bar, or sheet iron, by means of the waste flame of other furnaces, is scarcely worth attempting, for the inconveniences attending this practice, added to the loss of iron which results, may, in most cases, counterbalance the gain in fuel. Nevertheless, where both skill and industry have been brought into requisition, the waste heat from reheating furnaces has, in some cases, been successfully employed in heating sheet iron, by conducting the flame over a layer of coke or charcoal. The waste flame of the charcoal forges is quite bulky, but of very low temperature; it can not serve with advantage for any other purpose than the heating of pig iron, and blast; but if this heating is well managed, twenty-five

to thirty per cent. of coal may be saved. The best use which can be made of this flame is to apply it in the generation of steam. If the attempts which have been made, in Eastern Pennsylvania, to construct light and fast working steam hammers shall ultimately prove successful, it may not be far amiss to conjecture that the charcoal fire will successfully rival the puddling furnace, at least in those cases where mineral coal commands a comparatively high price.

b. The waste heat of the blast furnace is, as we have stated, immense; we shall not greatly err, if we assert that 150 pounds of coal are used, where only ten pounds are actually needed to produce that amount of heat and gas which is required to revive and melt a given quantity of iron. Practical investigations on a small scale have shown that thirty pounds of coal are sufficient to produce 100 pounds of iron. Be this as it may, this much is certain, that an immense quantity of heat is wasted, to employ which various means have been resorted to. One of the most common applications of the top flame was, at one time, to the burning of lime; for this purpose it is excellently adapted, producing a fine article. The burning of lime is admissible at every furnace where heat is wasted; apart from the generation of steam, nothing is so well calculated to absorb the heat, which is otherwise of no use, as this process. The waste heat from the blast furnace has also been employed to heat the blast; but the temperature of the trunnel-head flame is so high, that the heating apparatus cannot well be applied directly to the throat of the furnace; in this case, the conducting of the flame under a steam boiler, before it enters the hot blast stove, is a preferable arrangement. In some establishments of France and Germany, though not in this country, waste heat is employed in charring wood, stone coal, or turf. Such an application is advantageous where the products of distillation, such as pyroligneous acid and coal tar, are of value. But this is the case only to a limited degree in this country. The charcoal or coke, which is then made in iron retorts, is inferior to kiln charcoal; and if the yield were as great in kilns as in these retorts, no profit would result from thus making charcoal, unless the products of distillation were worth the labor spent in obtaining them. The most common application of the top flame is, at present, to the generation of steam for the blast machine; it is generally applied at anthracite furnaces, and, in a great measure, at charcoal furnaces. This is a highly judicious and economical application; it facilitates, in a great