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which are secured by exposing the ore to the action of the gases lower down in the furnace, which in this case was one of 48 feet in height:

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Carbon deposition took place upon two different occasions, under the circumstances given below, on exposing calcined Cleveland stone to the action of the escaping gases:

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The intensely heated gases, which ascend from the hearth, having to perform the duty of reducing the ore as well as to heat the materials, the point which has to be kept in view in the construction of the blast furnace is, that its capacity should suffice for the heated gases to be retained among the solids long enough to communicate to the latter as much of their sensible heat as is possible, and to become as completely saturated with oxygen, as the nature of the chemical action will permit. These two objects seem to be attained in the Cleveland district, when the furnace has a height of 80 feet, with an interior capacity of about 12,000 cubic feet. These dimensions enable the gases to be cooled down to such a point, and to be so saturated with carbonic acid, as to retain little or no further power of reducing the ironstone of the country. The correctness of these views has been made apparent by the fact that furnaces, mentioned as having been constructed upwards of 103 feet high, and others nearly as lofty, with a capacity of 40,000 cubic feet, have failed to show any marked advantage, so far as economy of fuel is concerned, over that which has been frequently obtained in those of more moderate dimensions.

Let us now consider the structural error in a furnace to be in the opposite direction; i.e., that instead of being unnecessarily high and capacious, it is insufficient in both respects.

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The accompanying sketches are intended to afford a general idea of the temperatures of the materials filling two furnaces-one 80 feet high with boshes of 20 feet, and the other 47 feet in height with boshes of 16 feet. The capacities are 15,400 and 6,000 cubic feet respectively.

By drilling holes in the sides of the two structures the temperature of each was roughly ascertained, and the figures denoting these are inscribed along-side of each of the drawings. The indications of temperature given in the sketches must only be considered as comparative; for it is very possible that the contents of the furnaces at a distance from the walls may be hotter than is indicated by the figures. Indeed, looking at the rate at which reduction is carried on in the first 16 feet of the height of the larger furnace, of which space not above one-half on an average is actually occupied by the materials, it seems very probable that the interior of the mass is somewhat more highly heated than I have supposed.

The advantages possessed by the larger furnace are firstly, that the gases pass away cooled, as far as it is practicable to effect this; and secondly that the deoxidation of the oxide of iron is performed in a portion of the furnace where the temperature is so low, as to avoid as much as possible the carbon acting on the carbonic acid generated by the act of reduction. The comparative magnitude of this zone of moderate temperature in each furnace can easily be appreciated by an inspection of the two sketches. In the larger one the contents do not exhibit a dull red heat until a depth of 16 or 17 feet is reached, whereas in the other this temperature manifests itself at a depth of about 9 or 10 feet. In each case the distance is reckoned from the charging plates.

It might be supposed at first sight that the conditions of the two furnaces could be brought into harmony by diminishing the rate of driving in the lesser. The increased period of time however, during which the ore would then be exposed to the action of the heated gases, only brings the hotter zone nearer the top of the furnace, and an actual trial of slower driving, extended over some time, induced me to think that there was no gain to be expected from a change of that kind.

A comparison between two furnaces, of 11,500 and 6,000 feet respectively, taken from actual experience, is perhaps the simplest mode of pointing out the points of dissimilarity.

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From this statement it will be perceived that in the smaller furnace there is a greater weight of blast consumed for a given quantity of metal, and a larger volume of gases emitted, owing to the larger weight of coke burnt as compared with the larger furnace. The use of more coke demands more limestone, to flux the ash it contains; which necessitates further increase of coke, from the heat required to decompose the carbonate of lime, as well as to provide carbon to split up the further quantity of carbonic acid liberated. Besides this, additional fuel is rendered necessary, in order to melt the larger quantity of slag thus formed.

The following statement exhibits the mode by which the performance of the larger blast furnace was ascertained:

Seven specimens of gases were collected during 3 hours and 20 minutes, so as to avoid the fluctuations in composition already spoken of; and the analyses, to ensure accuracy, were all made in duplicate.

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From these figures the average composition by weight was cal

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