number of calories, and that the gases carry off the same dose of sensible heat. The ideal working supposes that the reduction of the oxide of iron is effected by the CO only, without intervention of solid carbon. But it is easy to calculate the weight of CO transformed to CO2 by the reduction of the ores—at least if we take account only of the oxide of iron properly so called. For each lb. of pig iron we have 0.97 iron and 0.97 × of oxygen, and this oxygen transforms a weight of CO into CO2, containing The caloric produced by this carbon in its successive transformation into CO, near the twyres, and into CO2, in the zone of reduction, is 0lb 312 x 8080 2521 calories. = which has been burned near the twyres, and this gives as the final consumption 01·030 + 0·312 + 0·496 = 0.838 instead of 11., which, for the case of an ideal working, gives an economy of 0lb 162 per lb. of pig yielded = 16% CO2 Let us now show that the proportion CO will be, in an ideally perfect working, as follows:— 0.3120-072 (from limestone) =0.384 carbon in CO2 Blast Furnaces.-It has now been shown by these examples CO2 that the ratio in the escaping gases may vary between CO wide limits. In the modern furnaces of Cleveland, the proportion is generally between 0.50 and 0.70 when the working is good; but it is only 0.35 to 0.40 when the furnace is in bad condition. And if we could attain to the ideal working, it would be as high as 1.217. We thus see that this ratio is as it were the measure or index of the degree of perfection of the working of furnaces. Of a truth, this ratio is found to vary from one district to another, according to the richness of the ores and their quality, the nature and purity of the fuel, the proportion of flux employed, the number of the pig-iron yielded, etc. etc. But in any given ironwork, or in a given district, this ratio will fall or rise,—will recede from or approach to the ideal figure as the furnace works well. It thus appears very important to be able to determine this proportion exactly by experiments easily multiplied. We have already seen by the examples I have quoted that, when the ratio is known, we can easily calculate the absolute quantities of the two gases, and consequently also the sum of the caloric given off by combustion in the blast furnace. 3 It has been shown above that the direct determination of this ratio allows of our fixing, in a rigorous manner, not only the quantities of CO and CO2, but also very approximately the weight of air for blast and of the escaping gases, and the composition complete of these latter. 87. Weight and composition of the escaping gases.—The ordinary or normal working of the blast furnace gives the data of the weight of the flux and of fuel consumed per unit of pig-iron produced. We know also from the quality of the pig yielded the proportion of carbon united to the iron. We may estimate this at 3 % in ordinary forge iron. Let a the carbon per lb. of pig, b the carbon contained in the flux, and hence p the total carbon in the gases = a + b 0.03. If we put y for the weight of CO, and m for the CO2 proportion we have my for the weight of CO2, and then CO' for determining y we have the equation (1.) 3 7 3 y+ my = p 11 which formula expresses that the quantities of carbon in CO and CO2 are equal to the total carbon in the gases. Hence we have 77 p The oxygen contained in the gases will, in like manner, be equal to the oxygen furnished by the blast, and by the charges of ores and flux, which is expressed by the equation— (2.) in which represents the oxygen of the blast, and d represents that furnished by the ores and the CO2 of the flux. From this equation we find To calculate x, we must first find the value of d. If only the oxide of iron were reduced, it would be easy to determine d exactly. It would be composed of two terms, the oxygen united to b carbon in the CO2 of the flux, that is then the oxygen combined with 0.97 iron or 8 b ; and 3 we suppose the iron in the state of peroxide; so that we should have But pig-iron generally contains, besides 0-03 of carbon, other elements, such as silicium, manganese, etc. etc., phosphates derived also from the ores. If we knew the composition of the pig-iron, it would be quite as easy to calculate the oxygen derived from these various elements, as of that furnished by the peroxide of iron. Neglecting this correction, we shall generally get a value of d rather too little, because this would be to suppose that these elements united with as much oxygen as the iron, and silica at least gives a much larger proportion. If we start from an average composition of pig-iron, we shall at all events approximate the truth more nearly, and thus obtain values of d and of x very little different from the true values. Suppose a gray forge pig (Nos. 3 and 4 of English marks). We may admit as its composition, if there be little manganese According to the equivalents, the silica contains 24 of oxygen for 21 silicium, or 8 for 7; the oxygen derived from the silica = 8 0.02; and this expression would be near the truth if, for a part of the silicium, there were substituted phosphorus and sulphur, for phosphoric acid contains 50 for 4Ph, and sulphuric acid contains 30 for 2S.* As to the earthy metals, we know that in Lime, the O corresponds to Magnesia Alumina metal 景 66 66 We may therefore admit, as an approximate average, of 01b .01. At all events, on such a feeble quantity the possible error will be insignificant. According to the above reasoning the corrected value of the total oxygen in the ore and flux will be 8 1 3 7 instead of the former expression, which gave b+ (2.91). *Sulphuric acid furnishes for equal weight more oxygen than does silica, but this excess is compensated by the circumstance that the greater part of the sulphur of pig-iron is derived from sulphurats and not from sulphates. |