instantaneously transformed into carbonic oxide,* and this gas, in its passage up the body of the furnace, acts more or less directly in reducing ores-that is to say, with or without the aid of the solid carbon. The reduction of the oxide of iron in the blast furnace may take place in three different ways, according to the portion of the furnace we examine. In general, the oxide of carbon (CO) is transformed into CO2, which escapes as such by the furnace top without other reaction. In other positions, the CO2 thus produced becomes again, partially at least, CO by burning solid carbon, which comes in the end, both in its chemical and calorific relations, to be the same thing as if the solid carbon acted directly on the oxygen of the ores, yielding thus either CO2 or CO. These three ways of reduction may be represented by the following formulas: 1. 3CO + Fe22033CO2 + 2Fe; It may be at once remarked that the two first ways of reduction are not in fact realizable, if we adopt the propor * We know by the experiments of MM. H. Deville and Cailletet, that near the twyres there is a mixture of unconsumed air and of carbon in minute state of subdivision, by the fact of dissociation; but higher up, the temperature falls sufficiently to determine the definite combination of carbon and oxygen, in the form of carbonic oxide. As to the question, whether in the first moments CO2 or CO be produced, it is simply impossible to answer it; and, truth to say, almost idle to discuss it. We may, however, remark, that when carbon is burned on fire bars, the CO is not really produced till the bed of fuel be sufficiently thick to allow of C being taken up; and thus there can be little doubt that carbonic acid is produced in the first place. tions given in the formulas. In these conditions the metallic iron would be partially reoxidized by the carbonic acid. We know by the experiments of M. Debray, confirmed by Mr. Lowthian Bell, that, in presence of equal volumes of CO and CO2, peroxide and metallic iron are both brought to the state of protoxide. But though these two first modes of reduction are impossible taken singly, they generally help, with the third mode, in producing the final result; and, in fact, the gases taken at the furnace-top are always composed of a mixture of CO and CO2. According as the one or the other mode of reduction has the greater share in the final result, the proportion of CO or CO2 in the gases taken at the furnace-top is the greater. But it is easy to show that these three modes of reduction require very different quantities of caloric; and, in this point of view-that is, in reference to the consumption of fuel-it is not a matter of indifference which of these reactions takes place in blast furnaces. § 4. Quantities of caloric absorbed and given off in blast furnaces. Let us determine the quantities of caloric absorbed and given off in the three modes of reduction we have been considering. The caloric absorbed is the same in all three cases:-it is the caloric which a lb. of oxygen would produce in uniting with metallic iron to make peroxide. Let us put C, for the moment, for this number of calories. In the first case, the number of calories given off results from the transformation of CO into CO2. Now each lb. (or other unit of carbon) produces 2403 calories (referred to Centigrade scale and same unit), in talking up 4 lb. of oxygen from the oxide of iron. Hence it follows that for each lb. of oxygen the transforma tion of CO into CO2 is accompanied by the giving off of caloric of× 2403 = 4205 calories. Thus the difference (C-4025) represents the calorie required for the reduction of the peroxide of iron under the action of CO passing to the state of CO2, for each lb. of oxygen taken up. 3 In the second case, the carbon is transformed into CO2 by the oxygen of the ore. Under these conditions the lb. of carbon develops 8080 calories in taking up lb. of oxygen, and this gives x 8080 3030 cals. for each lb. of oxygen. Consequently C-3030 is the caloric necessary for reduction, when this is effected by the solid carbon yielding CO2. Lastly, in the third mode of reduction the reaction would be that the oxygen of the ores produced CO directly by means of the solid carbon. But a lb. of carbon gives off 2473 calories* when it forms CO: and as it then takes up lb. of oxygen, the caloric given off by each lb. of oxygen is × 2473 1855 cals. Consequently the difference C-1855 represents the number of cals. required for reduction when this is effected by solid carbon burning to CO. In order therefore to take up a lb. of oxygen from the peroxide of iron, we have the number of calories given by the following formulas: C-4205 cals. C-1855 "6 * This number, to which we shall have to recur frequently, is determined by the following reasoning. The caloric produced by a lb. of carbon giving CO2 is evidently equal to the sum of the two results of the transformation of C into CO and then of CO in CO2. But 1 lb. carbon gives 7 lbs. CO, and as each lb. of CO gives off 2403 cal. in burning, we should have for the lbs. × 24035607, which leaves for the transformation of C into CO, 7 8080-5607=2473 cals. The value of C is not rigorously known. It may indeed vary with the physical condition of the peroxide, but it appears to be confined between the limits of 4600 and 4500 calories, so that the first mode of reduction above represented is effected almost without absorption of caloric. Again, and whatever may be the value of C, it is evident that this mode of reduction is much the most favorable, and that the third mode is very disadvantageous. It is therefore of importance that the reduction of the ores in blast furnaces should be effected as far as possible by the first mode only-that is to say, by the CO being transformed into CO2—or, in other words, without consumption of solid carbon. This is what we shall allude to in future as the ideally perfect working of a furnace. When this mode of working is realized, the reactions will be of the simplest kind. The CO produced near the twyres will reduce the ores and be transformed to CO2, and this in its turn will leave the furnace without reaction on the solid carbon. In this case all the carbon of the charges will pass through the furnace without other alteration than a gradual heating, and this carbon will be finally burned to CO under the action of the blast of the twyres. To realize this ideal working, or at least come as near to it as possible, the reduction must take place in a region of the furnace in which the temperature is relatively feeble, otherwise the CO2 thus generated will constantly re-form CO at the expense of solid carbon. The furnaces must therefore be sufficiently capacious, or sufficiently high to insure that the whole upper region should remain at this comparatively low temperature; but at the same time the ascent of the gases must be so rapid that it shall remain a very short time in contact with the solid carbon. It is evident besides that ores easily reduced (soft porous ores) will help to realize the ideal working more than compact siliceous ores. But, in general, whatever be the ore, the reduction can only take place completely in the hot regions in which the CO2 will continually get reconverted to CO, and this will be the case more particularly with other oxides than those of iron-such as silica, lime, magnesia, and the oxide of magnesia; the reducof these oxides will always require the direct or indirect aid of solid carbon. § 5. The economical working of the furnaces varies with the CO2 ratio of in the gases.-From what precedes it results, that CO the relative quantities of CO2 and CO in the gas given off from the furnace depends essentially on the mode of reduction for a given constitution of the charges. And consequently. the higher or lower proportions between the two gases will allow of our appreciating the degree of perfection of the working of the blast furnace.* One or two examples will be sufficient to prove this. We shall see very soon that in the same ironwork, with the same ores, producing the same No. of pig, the temperature of the blast being the same, we find the proportions in the escaping gases as follows, according to the section and dimensions of the furnaces: 0-3 of the total carbon under the form of CO2+ 66 66 CO * See, for announcement of this fundamental law, section xxxiv. of Mr. Bell's work. + Abstraction is made here of the CO2 in the flux. We have at present to do with the products of the carbon consumed. |