descended through the first quarter of the height, while, when charcoal is the fuel used in the furnace, reduction takes place at a relatively higher temperature, and the charge descends about half way down the furnace before any considerable reduction begins. As the Cleveland furnace is usually considerably higher than one employing charcoal as fuel, it follows that the zone of principal reduction is usually about 60 ft. above the bottom of the hearth in a Cleveland furnace, but only about 20 ft. high in a charcoal furnace ; hence the period of heat interception is much longer in a Cleveland than in a charcoal furnace. The fuel consumption is, however, slightly less, and the proportion of carbon dioxide in the gases distinctly greater in the charcoal furnace, results which are no doubt connected with the nature of the reaction, and the position in the furnace where the principal reduction occurs. The reactions which take place in a coke blast furnace may be conveniently divided into two classes; first, those which are essential for the production of heat and the reduction of the ore; and, secondly, those which are more or less variable or accidental, according to the particular materials which may be employed, or the special product which is desired. The first class of reactions are exothermic, or heat-producing, and in their simplest form may be divided into two portions and represented as follows: (1) When the heated air enters the blast furnace it is immediately converted into carbon monoxide, the reaction being It is worthy of note that the reaction thus taking place in the hearth of the blast furnace is quite different from that with which we are familiar in a gas producer, a cupola, or an ordinary fire. In these cases the carbon is first burned to form carbon dioxide, and this after it is formed reacts with more carbon to produce carbon monoxide, thus— but while carbon when burned at a comparatively low temperature produces carbon dioxide, the condition is altered when the temperature is raised, since carbon dioxide is dissociated at a high temperature with the production of carbon monoxide and oxygen. In blast furnaces using cold blast, or air which has been heated only to a moderate temperature, the zone of combustion extends for a considerable distance in front and above the twyers; but it has been shown experimentally that in a coke blast furnace using blast heated with firebrick stoves, no free oxygen can be detected in the gases at a height of only two feet above the twyers. When the enormous volume of air under high pressure which is introduced into the furnace is borne in mind, it may well be a matter for surprise that the combustion of the oxygen should be so complete; but it is evident that when the temperature of the hearth is sufficiently high, the production of carbon monoxide is practically instantaneous. (2) The other important exothermic reaction takes place near the top of the furnace, and the heat thus generated is much less in amount than that produced in the hearth. The carbon monoxide now reacts upon the ferric oxide in the ore, with the production of carbon dioxide and metallic iron; but since it is found that in order to carry on the reduction satisfactorily it is necessary to have in the issuing gases at least two volumes of carbon monoxide to one volume of carbon dioxide, the equation may for convenience be written as follows = Fe2O3 + 3 CO + 6 CO Fe2 + 3 CO2 + 6 CO, in which the excess of carbon monoxide required is represented on both sides of the equation. The second class of reactions are more numerous and are all endothermic, or heat absorbing. As already explained, they vary in character and amount according to local circumstances; they include the decomposition of limestone and the formation of slags, the heat absorbed in which will vary, in the first case, according as to whether free lime or limestone is employed, and in the second, with the proportion of gangue. A reaction known as carbon impregnation also takes place during the descent of the charge in the furnace; by this a certain proportion of the carbon monoxide of the ascending gases is decomposed in contact with metallic iron, with the formation of ferrous oxide, and the deposition of finely divided carbon in the mass. the temperature increases in the upper part of the zone of fusion, the ferrous oxide is reduced with the liberation of carbon monoxide, which As passing upward leads to the addition of an appreciable amount of combined oxygen to the issuing gases. Other reactions which are endothermic and variable in amount, are those which are connected with the reduction of such proportions of silicon, phosphorus, sulphur, manganese or other elements as are found in the pig iron. It may be noted here that grey pig iron usually contains more silicon, and not unfrequently more carbon, than white iron; and as the reduction of silicon is an endothermic one, it naturally follows that the proportion of fuel required to produce grey iron is somewhat greater than that necessary to make a white pig. It was first observed by Bunsen and Playfair in 1845, and has since been confirmed by other observers, that there is a considerable proportion of potassium cyanide present in the gas in the lower portion of the furnace, and it is believed that this cyanide accumulates in the furnace and exerts a not inconsiderable influence in assisting the final reduction, but the relative importance of the cyanide reaction is at present undetermined. Charging the Blast Furnace. The early forms of blast furnace were frequently built against a bank of earth so as to allow of the material being conveniently wheeled in hand barrows and emptied into the furnace; but as the production increased such primitive methods were gradually replaced by the use of inclined planes worked by steam engines, or later by lifts and hoists of various forms, actuated either by steam, compressed air, hydraulic power, or more recently by electricity. In all such cases the materials are brought from the lift to the furnace top in hand barrows and emptied into the furnace by manual labour. But the enormously increased output of modern times, amounting now to close upon five thousand tons per week from a single furnace, has caused any method of charging by hand barrows to be inadequate and inconvenient, and automatic charging appliances have in consequence been introduced. The first plant of this kind was erected in the Duquesne works, near Pittsburg, in 1896, and I had an opportunity of seeing it in operation in 1902; with modifications in detail the improvement is being introduced into the larger iron works. A cross section of the blast furnace plant at Duquesne is given in fig. 8. This is taken from a paper read by Mr Head before the S. Staffordshire Iron and Steel Institute in March 1898, and illustrates the handling of the ore from the car to the stock-yard, and from the stock-yard, or from the car direct, as required, to the bottom of the automatic charging apparatus, and hence into the furnace top. The usual forn of automatic charging apparatus as at present employed consists of a double line of steeply inclined rails, supported on a frame work of rivetted steel, and passing from the charging hoppers on the ground level to a suitable position above the furnace top. On these lines run two skips made of steel plates, and arranged so that the descent of one skip serves to counterbalance the ascending weight of the other, so that only the weight of the load has to be raised. By an apparatus of this kind, electrically driven, FIG. 8.-Section showing method of handling ore at Blast Furnaces, it is possible for one man remaining at the bottom of the furnace to charge the whole of the materials necessary for the production of the large output of a modern furnace. In order to allow of the gas being collected and utilized as usual, it is found necessary with an automatic charging apparatus to provide a double cup and cone arrangement, as shown in fig. 9. The Blast used in the Blast Furnace. The air used for the combustion of the fuel in the blast furnace was originally supplied by means of bellows worked by manual labour, and simple appliances of this kind are still used in India and elsewhere. Such simple forms of apparatus were gradually replaced by larger bellows driven by water power, and subsequently by the |