Page:Encyclopædia Britannica, Ninth Edition, v. 13.djvu/317

IKON 301 and Steel Institute, 1871, i. p. 433, illustrates the arrange ment. That part of the gas not consumed in the coking re tort flues is led off by the usual bell and cone arrangement. Before these chambers were erected the quantity of raw coal requisite to make a ton of pig from the Lanarkshire ironstone averaged about 52 o cwt. ; the addition of the coking chambers reduced the amount of coal to 33 5 cwt., producing a saving of 19 cwt. of raw coal, equivalent to upwards of 12 cwt. of coke per ton of iron. According to Lowthian Bell this result is largely duo to the increase in the height of the furnace produced by the addi tion of the coking chambers ; i. c. , a large proportion of the saving (estimated by Bell at about one half) would have been brought about by an increase in furnaco height, even though the upper part were not specially heated by the combustion of waste gases, the balance being due, first, to the avoidance of a large portion of the heat absorption during the coking of the coal that would other wise have taken place at the expense of the heat developed by chemical changes in the upper part of the furnace, owing to the supply of heat from the combustion of waste gases in the external flues, and, secondly, to the modifying action of the hydrocarbons developed on the chemical changes themselves, the direction of the modification being that of increased rate of reduction of iron oxide. In any case, the consumption of fuel is by no means inferior to that which with the most advantageous conditions will suffice to smelt a given iron ore ( 21). For further details see Journal Iron and Steel Institute, loc. cit., and 1871, ii. 228. A modification of this furnace has been tried, in which the coking chambers at the top are connected with condensers for collection of tar and am- moniacal liquor ; the fuel only is placed in these chambers, the mine and flux being introduced at their base. Double Hows of Tuyeres. Experiments have been made, notably at Pittsburg, U.S., on furnaces with two sets of tuyeres, one row at a lesser height above the sole than that of the other row, both rows used simultaneously; the general effect has been found to be the reverse of advantageous. It is, however, frequently convenient to have two or more tuyeres symmetrically disposed round the furnace at a somewhat higher level than those ordinarily used, the higher series being employed, not in the ordinary working of the furnace, but only in case of certain derangements of working such as scaffold ing, &c. ; accordingly several furnaces of recent construction, especially in America, have been thus fitted with "auxiliary tuyeres," at 16 to 18 inches level above the others, ready for use when occasion needs. In certain cases when scaffolding had taken place to such an extent that the furnace did not give any fused matter at all at the hearth, and it was probable that it would have to be put out of blast and partly unbuilt, proper working has been brought about and the obstruction removed by what was thought when first practised to be a desperate remedy, viz., cutting holes in the shaft at some elevation (15-20 feet) above the tuyeres and intro ducing by means of temporary tuyeres blast at the orifices thus formed, so as to flux away the obstructing matter. In certain American works scaffolds have been melted away by introducing a little above the tuyere a pipe communicating with a barrel of petro leum, so as to create an intense local heat by the combustion of the petroleum allowed to run in in a gentle stream. 13. Hoists and Lifts. Except when the natural varia tions in the level of the ground permit of the materials being drawn in waggons or trucks to the top of the furnace directly, lifts of various kinds are employed to raise them. " Water lifts " consist of a pair of chambers or cages working in guides suspended to the two ends of a chain passing over a pulley, and provided with water boxes, so that a stream of water from a tank or reservoir at a higher elevation can be directed into the uppermost waterbox, rendering that heavier than the other, when the weighted cage descends with the empty trucks drawing up the other one with the trucks laden with materials, the rate of descent being regulated by a brake. In frosty weather lifts of this kind are apt to become impracticable. Hydraulic lifts are sometimes used, consisting of a similar chamber suspended from a chain passing over multiplying pulley blocks and attached to the piston of a hydraulic ram, so that when the ram makes a stroke the chain draws up the cage ; if the blocks multiply tenfold a stroke of 7 feet of the ram draws up the cage 70 feet. At the Bethlehem Works, U.S., an hydraulic hoist is employed in which the relatively short stroke of the ram is made to raise the cage through a much greater height by making the ram actuate an axle by means of a rack and pinion, a large wheel being fixed on the axle over which the cage rope passes. Besides these lifts, an inclined plane and stationary engine, or a vertical lift like a colliery winding engine, is sometimes employed. Pneumatic lifts of various kinds are also in use, one consisting of a tall bell immersed in a water tank like an exaggerated thin gasometer; the bell is attached to the cage (underneath it) and also to a chain passing over a pulley to a counterpoise, the weight being so arranged that the bell, when not containing air under pressure, together with the cage and empty trolly, is heavier than the coun terpoise, and sinks when a valve is opened, so that the internal air pressure becomes atmospheric; whilst on closing the valve and forcing air in, the water inside the bell is partially displaced, and the bell and cage, being relatively lighter, rise like an ordinary gasometer. Gjers s pneumatic lift is a piston box, such that, the air being exhausted or compressed under the piston which is connected with the cage, a motion up or clown as the case may be Ls brought about. Fig. 14, taken from a paper by Gjers.in the Journal Iron and Steel Institute, 1871, ii. 209, illustrates the mode of action the cylinder is about 30 inches dia meter, the piston being connected with the travelling plat form (through the centre of which the cylinder passes freely) by four wire ropes passing over pulleys overhead ; the platform runs along guides bolted to the cylinder. The platform and empty barrows being at the top, air at about 2 ft) pressure per square inch is forced into the cylinder underneath the piston, which suffices to make it ascend, and consequently to cause the table to descend ; when barrows full of mine, coke, &c., are wheeled on to the platform, the air is sucked out from underneath the piston so as to make a vacuum of about 4 Ib (i.e., the pressure is reduced from 14 to 10 K> per square inch) with heavy loads, and propor tionately less with lighter ones, when the atmospheric pressure now forces the piston down and draws the cage up. The strain on the ropes is thus diminished, whilst the objection to water lifts of being unworkable in frosty weather is entirely done away with. For heavier weights two larger cylinders are employed, working conjointly with the cage or platform between them. 14. Production of Blast. The earliest blowing machines were made of goats skins, inflated by hand by pulling cords, and compressed either by standing on them or by a weight or a bent bamboo acting as a spring, &c. ; such rude arrange ments are still in use amongst certain Eastern nations ; a kind of rudimentary cylinder blowing machine is also employed in certain districts, consisting of a hollowed log with a piston packed with feathers, leaves, <fcc. About the middle of the 17th century the trompe appears to have been first invented, probably in Italy. The action of this arrangement depends on the suction of air into a stream of falling water running from a tank by an orifice not too far from the surface of the water, just as occurs on pulling out the plug of an ordinary lavatory basin so as to discharge the water therein ; the air carried down by the water is discharged into a chamber with an outlet at bottom for the water and one at top for the air, so that as long as the stream of water is kept up a continuous air current passes out of the air hole, the force of which is regulated by a plug- valve attached to a lever and cord, so that the furnace- man can at will diminish or increase the amount of falling water. In practice the trompe only utilizes a small frac tion of the power of the descending water. It is of course inapplicable in cold climates during frost ; a serious dis advantage too is the fact that much fine spray accompanies the blast and interferes with the production of heat thereby. With a fall of 20 to 30 feet a well-proportioned trompe will deliver a sufficient air supply for a Catalan forge at a pressure of about 9 or 10 centimetres of mercury (about ^ atmosphere = nearly 2 tt> per square inch).