been; nor, indeed, shall I enter into detail, farther than, to the general scientific reader, may be proper to elucidate Mr. Neilson's invention. In making cast-iron, then, the materials made use of were three,--the ore, the fuel, the flux. The ore was clay iron-stone, that is to say, carbonate of iron, mixed, in variable proportions, with carbonates of lime, and of magnesia, as well as with aluminous and silicious matter. The fuel made use of at Clyde Iron-works, and in Scotland, generally, was coke, derived from splint-coal. During its conversion into coke, this coal underwent a loss of 55 parts in the 100, leaving 45 of coke. The advantage of this previous convertion consisted in the higher temperature produced by the combustion of coke, in consequence of none of the resulting heat disappearing in the latent form, in the vapours arising from the coal, during its convertion into coke. The flux was common limestone, which was employed to act upon the aluminous and silicious impurities of the ore, so as to produce a mixture more easy to melt than any of the materials of which it was made up, just as an alloy of tin and lead serves as a solder, the resulting alloy being more easy to melt than either the lead or the tin apart. These three materials--the ore, the fuel, and the flux-were put into the furnace, near the top, in a state of mixture. The only other material sup plied was air, which was driven into the furnace by pipes from blowing apparatus, and it entered the furnace by nozzles, sometimes on two opposite sides of the furnace, sometimes on three, sometimes, but rarely, on four. The air supplied in this manner entered near the bottom of the furnace, at about forty feet from the top, where the solid materials were put in. The furnace, in shape, consisted, at the middle part, of the frustums of two cones, having a horizontal base common to both, and the other and smaller ends of each prolonged into cylinders, which constituted the top and bottom of the furnace. The whole of the materials put into the furnace, resolved themselves into gaseous products, and into liquid products. The gaseous products, escaping invisibly at the top, included all the carbonaceous matter of the coke, probably in the form of carbonic acid, except only the small portion of carbon retained by the cast-iron. The liquid products were collected in the cylin drical reservoir, constituting the bottom of the furnace, and there divided themselves into two portions, the lower and heavier being the melted cast. iron, and the upper and lighter being the melted slag, resulting from the action of the fixed portion of the flux upon the impurities of the fuel and of the ore. II. Thus much being understood in regard to the process of making castiron, as formerly practised, we are now prepared for the statement of Mr. Neilson's improvement. This improvement consists essentially in heating the air in its passage from the blowing apparatus to the furnace. The heating has hitherto been effected by making the air pass through cast-iron vessels, kept at a red heat. In the specification of the patent, Mr. Neilson states, that no particular form of heating apparatus is essential to obtaining the beneficial effect of his invention; and, out of many forms that have been tried, experience does not seem to have yet decided which is best. At Clyde Iron-Works, the most beneficial of the results that I shall have occasion to state, were obtained by the obvious expedient of keeping red-hot the cast-iron cylindrical pipes conveying the air from the blowing apparatus to the furnace. III. Such being the simple nature of Mr. Neilson's invention, I now proceed to state the effect of its application. During the first six months of the year 1829, when all the cast-iron in Clyde Iron-Works was made by means of the cold blast, a single ton of cast-iron required for fuel to reduce it, 8 tons 1 cwt. of coal, converted into coke. During the first six months of the following year, while the air was heated to near 300° Fah., one ton of cast-iron required 5 tons 3 cwt. of coal, converted into coke. The saving amounts to 2 tons 18 cwt. on the making of one ton of castiron; but from that saving comes to be deducted the coals used in heating the air, which were nearly 8 cwt. The nett saving was thus 2 tons of coal on a single ton of cast-iron. But during that year, 1830, the air was heated no higher than 300° Fah. The great success, however, of those trials, encouraged Mr. Dunlop, and other iron-masters, to try the effect of a still higher temperature. Nor were their expectations disappointed. The saving of coal was greatly increased, insomuch that, about the beginning of 1851, Mr. Dixon, proprietor of the Calder Iron-Works, felt himself encouraged to attempt the substitution of raw coal for the coke before in use. Proceeding on the ascertained advantages of the hot blast, the attempt was entirely successful; and, since that period, the use of raw coal has been extended so far as to be adopted in the majority of the Scotch IronWorks. The temperature of the air under blast had now been raised so as to melt lead, and sometimes zinc, and therefore, was above 600° Fah., instead of being only 300°, as in the year 1830. The furnace had now become so much elevated in temperature, as to require water around the nozzle of the blow pipes, a precaution borrowed from the finery-furnaces, wherein cast-iron is converted into malleable, but seldom or never employed where cast-iron is made by means of the cold blast. What is called the Tweer, is the opening of the furnace to admit the nozzle of the blow pipe. This opening is of a round funnel-shape, tapering inwards, and it used always to have a cast-iron lining, to protect the other building materials, and to afford them support. This cast-iron lining was just a tapering tube nearly of the shape of the blow pipe, but large enough to admit it freely. Now, under the changes I have been describing, the temperature of the furnace near the nozzles, is such as to risk the melting of the cast-iron lining, which, being essential to the tweer, is itself commonly called by that name. To prevent such an accident, an old invention called the water-tweer was made available. The peculiarity of this tweer consists in the cast-iron lining already described being cast hollow instead of solid, so as to contain water within, and water is kept there continually changing as it heats, by means of one pipe to admit the water cold, and another to let the water escape when heated.* During the first six months of the year 1833, when all these changes had been fully brought into operation, one ton of cast-iron was made by means of 2 tons 54 cwt. of coal, which had not previously to be converted into coke. Adding to this 8 cwt. of coal for heating, we have 2 tons 13 cwt. of coal required to make a ton of iron; whereas, in 1829, when the cold blast was in operation, 8 tons 14 cwt. of coal had to be used. This being almost exactly three times as much, we have, from the change of the cold An incidental advantage attended the adoption of the water-tweers, inasmuch as these made it practicable to lute up the space between the blow-pipe nozzle and the tweers, and thus prevent the loss of some air that formerly escaped by that space, and kept up a bellowing hiss, which, happily, is now no longer heard. blast to the hot, combined with the use of coal instead of coke, three times as much iron made from any given weight of splint coal. During the three successive periods that have been specified, the same blowing apparatus was in use; and not the least remarkable effect of Mr. Neilson's invention, has been the increased efficacy of a given quantity of air in the production of iron. The furnaces at Clyde Iron Works, which were at first three, have been increased to four, and, the blast machinery being still the same, the following were the successive weekly products of iron during the periods already named, and the successive weekly consumption of fuel put into the furnace, apart from what was used in heating the blast: Tons. Comparing the product of 1829 with the product of 1833, it will be ob served that the blast, in consequence of being heated, has reduced more than double the quantity of iron. The fuel consumed in these two periods we cannot compare, since, in the former, coke was burned, and, in the latter, coal. But on comparing the consumption of coke in the years 1829 and 1830, we find, that although the product of iron in the latter period was increased, yet the consumption of coke was rather diminished. Hence the increased efficacy of the blast appears to be not greater than was to be expected, from the diminished fuel that had become necessary to smelt a given quantity of iron. On the whole, then, the application of the hot blast has caused the same fuel to reduce three times as much iron as before, and the same blast twice as much as before. The proportion of the flux required to reduce a given weight of the ore, has also been diminished. The amount of this diminution, and other particulars, interesting to practical persons, will appear on reference to a tabular statement supplied by Mr. Dunlop, and printed as an appendix to this paper. Not further to dwell on such details, I proceed to the last division of this paper, which is, IV. To attempt an explanation of the foregoing extraordinary results. Subsidiary to this attempt, it is necessary to discriminate between the quantity of fuel consumed and the temperature produced. For instance. we may conceive a stove to be kept at the temperature of 500° Fah., and lead to be put into such a stove for the purpose of being melted. Then, since the melting point of lead is more than 100° higher, it is evident that whatever fuel might be consumed in keeping that stove at the temperature of 500°, the fuel is all consumed to no purpose, so far as regards the melting of lead, in consequence of deficiency in the temperature. In the manufacture of cast-iron likewise, experience has taught us, that a certain temperature is required in order to work the furnace favorably, and all the fuel consumed so as to produce any lower degree of temperature, is fuel consumed in vain. And how the hot blast serves to increase the temperature of a blast furnace, will appear on adverting to the relative weights of the solid and of the gaseous materials made use of in the reduction of iron. As nearly as may be, a furnace, as wrought at Clyde Iron-Works in 1833, had two tons of solid materials an hour put in at the top, and this supply of two tons an hour was continued for twenty-three hours a day, one half-hour every morning, and another every evening, being consumed in letting off the iron made. But the gaseous material--the hot air-what might be the weight of it? This can easily be ascertained thus: I find, by comparing the quantities of air consumed at Clyde Iron-Works, and at Calder Iron-Works, that one furnace requires of hot air, from 2,500 to 3,000 cubical feet in a minute. I shall here assume 2,867 cubical feet to be the quantity; a number that I adopt for the sake of simplicity, inasmuch as, calculated at an avoirdupois ounce and a quarter, which is the weight of a cubical foot of air at 50° Fah., these feet correspond precisely with 2 cwt. of air a minute, or six tons an hour. Two tons of solid material an hour, put in at the top of the furnace, can scarce hurtfully effect the temperature of the furnace, at least in the hottest part of it, which must be far down, and where the iron, besides being reduced to the state of metal, is melted, and the slag, too, produced. When the fuel put in it at the top is coal, I have no doubt that, before it comes to this far-down part of the furnace--the place of its useful activity-the coal has been entirely coked; so that, in regard to the fuel, the new process differs from the old much more in appearance than in essence and reality. But if two tons of solid material an hour, put in at the top, are likely to effect the temperature of the hottest part of the furnace, can we say the same of six tons of air an hour, forced in at the bottom near that hottest part? The air supplied, is intended, no doubt, and answers, to support the combustion; but this beneficial effect is, in case of the cold blast, incidentally counteracted by the cooling power of six tons of air an hour, or 2 cwt. a minute, which, when forced in at the ordinary temperature of the air, cannot be conceived otherwise than as a prodigious refrigeratory passing through the hottest part of the furnace, and repressing its temperature. The expedient of previously heating the blast obviously removes this refrigeratory, leaving the air to act in promoting combustion, without robbing the combustion of any portion of the heat it produces. Such, I conceive, is the palpable, the adequate, and very simple explanation of the extraordinary advantages derived in the manufacture of cast-iron, from heating the air in its passage from the blowing apparatus to the furnace. Marischal College, Aberdeen, Jan. 10, 1835. APPENDIX. The blowing-engine has a steam-cylinder of forty inches diameter, and a blowing cylinder of eight feet deep and eighty inches diameter, and goes eighteen strokes a minute. The whole power of the engine was exerted in blowing the three furnaces, as well as in blowing the four, and in both cases there were two tweers of three inches diameter to each furnace. The pressure of the blast was 2 lb. to the square inch. The fourth fur$ nace was put into operation after the water-tweers were introduced, and the open spaces round the blow-pipes were closed up by luting. The engine then went less than eighteen strokes a minute, in consequence of the too great resistance of the materials contained in the three furnaces to the blast in its passage upwards. Materials constituting a Charge. lbs. 1829, Coke Roasted Ironstone, 1830 Table showing the weight of Cast-Iron produced, and the average weight of Coals made use of, in producing a ton of Cast-Iron, at Clyde Iron-Works, during the years 1829, 1830, and 1833, the Blowing-Engine being the Coals used 1833 Weekly pro- Average of [duct of Cast Coals used Iron by Four to 1 ton of Furnaces. Cast-Iron. TonsCwtQs. TonsCwQs duct of Cast- Cast-Iron. TonsCwtQs. TonsCwtQs. Jan. 6 176 10 2 The correspondent by whom we have been obligingly favored with the preceding paper, makes himself the following remarks on the subject of which it treats.-ED. M. M. "The best application of the hot blast that I have yet seen, is at the Wilsonton Iron-Works, near Lanark and Whitburn. At these works the heated air is never at a lower temperature than the melting point of lead (612°). This is readily tested by inserting a small bar of lead into an opening in the pipe for the purpose, a little way before it enters the furnace; the lead is instantly melted. When in good working order, zinc is fused (700°) in the same way. The air is heated in passing through a series of ironpipes of small diameter, fixed upright in a brick oven, and kept at a red heat; the heated air entering the furnace by four tweers. 'The Condie pipes,'-so called from Mr. John Condie, the manager of the Wilsonton Iron-Works, and late the Calder-last much longer than the ill-arranged heating-apparatus (with pipes of large diameter) at the Clyde Iron-Works, and effect a much greater saving in fuel. The raw coal when used as the fuel, has the disdvantage of soon filling the furnace, and is also found to produce an inferior quality of iron, to that made by use of coke. It is, therefore not unlikely to be soon, generally, given up." Lond. Mech. Mag. 19 162 4 0 7 2 4 18 3 4 0 5 2 2 17 O 0 0 5 2 2 5 0 2 Jan. 9 375 8 0 5 0 2 23 270 7 2 4 19 30 250 9 0 5 4 0 Feb. 6 265 3 2 5 5 5 |