cinder; that too much limestone is present; or that the burden is too light. If the iron is gray, the burden can be increased; but if it is white, this should be done cautiously. The withdrawal of a portion of the limestone will generally cure the evil, if the iron is white; but if it is gray, heavier burden is required. An almost invisible, lively flame at the top is significant of a healthy state of the furnace. The strength of the top flame of an anthracite furnace is proportionate to the amount of hydrogen the coal contains; and therefore this is, at best, but an uncertain indication of the state of the furnace. If the flame appears to be struggling to break through the timp, we may be sure that there is something wrong in the interior. But this depends upon the ore and coal, upon the form of the stack, and upon the blast. It is common where small ore is used, and where the hearth and top are narrow. The color of the timp flame is, like that of the top flame, indicative of the work in the furnace; and the rules applicable to the one are applicable to the other. The color of the flame will be more or less modified, according to the foreign matter the ore contains. If it contains zinc, arsenic, and lead, the flame will always emit white fumes, whether the furnace be cold or warm. If the materials contain common salt, the flame will emit fumes of the same color. Where the flame wavers, that is, where it is sometimes large and sometimes small, there is, without doubt, scaffolding in the lining. In this case, close watching of the sinking of the charges is needed. If it is found that all is not right, a reduction of the burden and an increase of blast must be resorted to.

hh. The gray metal, where the operation has been good, is very liquid; and keeps liquid for a long time in the pig bed. If of good quality, it is, even in the thinnest leaf, perfectly gray; but if inclined to white, the corners of the pigs, and thin castings, will be white. This iron appears perfectly white when liquid; while white metal is of a somewhat reddish, yellowish color, and throws out sparks. White metal chills very soon in the moulds, and assumes a rough, concave surface; it adheres, with much tenacity, to the iron tools used for cleaning the hearth. If metal contains sulphur, it is very apt to throw off fumes of sulphurous acid, or sulphuretted hydrogen. It throws off sulphurous acid, if smelted by coke or coal, and neutral or proper cinder; and sulphuretted hydrogen, if lime is used in large quantity, which is generally the case, because such iron cannot be smelted without an excess of limestone. Phosphorus can be detected only by an analysis of the metal.

ii. After the metal in the moulds is cooled, it is to be removed, weighed, and stored; and the sand of the pig bed dug up, wetted, and prepared for another cast. The cinders at small furnaces are easily removed in common carts. At stone coal furnaces, various methods have been devised to remove the large mass of cinder daily produced, of which that at present generally practiced at the anthracite furnace may be considered the best. It is this: Dig two round basins of about five or six feet in diameter, and two feet in depth, at the side of the stack. In the centre of each basin put a piece of pig metal, in an upright position. Around this pig metal, the cinders, which run into the basin, gather. A chain attached to a crane is then fastened to the pig metal, by means of which the cold cinder is placed upon any suitable vehicle, to be carried off.

A whole volume might be written without exhausting what could be said on the management of furnaces, and of blast furnaces in particular. But our space is limited, and we wish to avoid prolixity. Many occasions will arise, in the course of this work, which, we hope, will enable us to supply whatever deficiency our statement may, thus far, have exhibited.

X. Theory of the Blast Furnace.

It would be inconsistent with our object to enter, with scientific minuteness, upon this branch of our investigations. If we shall be able to convey to an intelligent mind a clear and comprehensive view of the operations which take place in the interior of the blast furnace, our design will be accomplished. It is evident our explanations must be somewhat of a speculative nature; but these are illustrated and confirmed by operations performed under the cognizance of our senses. In the previous chapters, we have related and reasoned upon matters which can be tangibly verified; but in the present instance, we are obliged to draw general conclusions from isolated, though well-established facts, by means of pure analogy an operation frequently and daily needed, and constantly performed by those engaged in the management of blast furnaces.

a. In the second chapter, we have spoken of fuel and its combustion, as well as of the different combinations which oxygen forms with fuel. We are forced to refer to that subject in the present instance, for the process of combustion must be well understood before we can understand the chemical operations which take place in a blast furnace. The fuel used in the blast furnace is composed, to a greater or less degree, of carbon, hydrogen, sulphur, and ashes.

If oxygen or atmospheric air combines with carbon, the result is either carbonic oxide or carbonic acid; at a high temperature, with a sufficient supply of air, always carbonic acid. A suffocated combustion, with an excess of fuel, generally produces carbonic oxide. The result of the combustion of hydrogen and oxygen is always water; that of the combustion of sulphur and oxygen always sulphurous acid.

Fig. 70.

b. Combustion in a blast furnace is, as may well be expected, of a somewhat complicated nature, and requires illustration to be understood. Fig. 70 represents a section of a blast furnace in operation, filled with coal, ore, and fluxes. If we introduce at a, a, the tuyere holes, a current of air or blast, combustion in the lower part will ensue; and, according to circumstances, the product will be carbonic acid of greater or less durability. But if we have an excess of fuel, and a limited supply of air, the final product of the combustion will be carbonic oxide. The primitive or immediate combination of carbon and oxygen at the tuyere forms carbonic acid; and this carbonic acid, in its progress through the coal, combines with more carbon, and forms carbonic oxide. Carbonic acid can not combine with any more oxygen than it already possesses; but carbonic oxide will combine with as much more as it already contains. Carbonic acid is of no use in reviving iron from the ore, for the ore is a combination of iron and oxygen; and carbonic acid could not abstract any oxygen from the ore. But carbonic oxide will combine with whatever oxygen is present in the interior of the blast furnace.

α

a

Theory of the blast furnace illustrated.

c. Practical investigation has demonstrated that the more friable and tender the coal is, the more easily oxygen combines with it; and that the more compact it is, that is, the greater its specific gravity, the greater is the difficulty with which it combines with oxygen. Heated air combines more readily with fuel than cold air,

and of course is more inclined to form carbonic oxide. Soft, open fuel and heated air form carbonic oxide, the agent in the reduction of the ore, more readily than hard coal; and we may conclude that charcoal and coke are more useful than anthracite coal in the manufacture of iron. According to this statement, the atmosphere of oxygen and carbonic acid will be a zone of greater or less radius, of which the mouth of the tuyere is the centre, as the circular lines in the engraving indicate. The radius of this zone has been found, by experiments made on furnaces, to vary, according to fuel and blast, from six inches to four or more feet. Applying what we have said to a common furnace, with grate and draft, the column of carbonic acid will be from six inches to four feet in height, if we pass a current of atmospheric air through hot and burning fuel. If the column of fuel is higher than this, the carbonic acid will be gradually converted into carbonic oxide. This process is exactly the same in the blast furnace; the oxygen of the atmosphere is gradually converted into carbonic acid, carbon with much oxygen—and then gradually into carbonic oxide, carbon with less oxygen. Where the atmosphere of carbonic acid ceases in the blast furnace, we may conclude that the working of the carbonic oxide. upon the ores commences, and that it changes more or less in its course upwards. The ascending current of the gases, in a blast furnace, consists, then, of carbonic oxide, hydrogen, and combinations of hydrogen and carbon. These latter gases are derived directly from the fuel, above the reach of free oxygen, and constitute gaseous combustibles, ready to unite with oxygen. Mixed with the above are steam, carbonic acid, and nitrogen-incombustible gases which have not the least influence upon the ore. The nitrogen is derived from the atmosphere.

The ascending current of the gases from the tuyeres differs in composition according to height; of course this composition will not be alike at a given height in two furnaces of different construction, and in which different materials are used. Actual experiments on furnaces carried on by hot blast and charcoal have furnished the following results:

Directly above the tuyere. Nitrogen. Carbonic acid. Carbonic oxide. Hydrogen.

We find here, what might have been expected, a gradual inThis is generated by the contact of The relative amount of the different

crease of the carbonic acid. carbonic oxide with the ore.

gases is not equal in different furnaces, for, in another case, the gases were mixed in the following proportions

The gases of a coke furnace exhibited the following composi

tion:

Directly above the tuyere. Nitrogen. Carbonic acid. Carbonic oxide. Hydrogen.

There are, particularly in coke furnaces, gases of a compound character; but these have little to do with practical results, the aim of our investigations.

From the above, it is apparent that the carbonic acid gas increases as the current of gas ascends; and that, on an average, one-third of the carbonic oxide has been converted into carbonic acid before escaping at the top. If the carbonic oxide is the only reagent in the conversion of ore into iron, we may conclude that one-third of the fuel has been properly applied for the purpose for which it was designed. We here have evidence that all the fuel has not done its duty; otherwise, all the carbonic oxide would have been converted into carbonic acid, and all the hydrogen into water. But such is not the case. If a furnace works well, there will be more carbonic acid at the top of the charges than there will be if a furnace works badly; this circumstance accounts for the different appearance of the trunnel head flame.

d. The theory of the reduction of ore will then be simply this: the gases ascending in the furnace leave a part of their positive elements to combine with the oxygen of the ore, that is, carbonic oxide leaves carbon, and, under peculiar circumstances, hydrogen may be retained. If carbonic oxide absorbs oxygen from the ore, it leaves of course metallic iron or protoxide, and the ore, in descending, will be a mixture of metallic iron and foreign matter.

If