Page:Encyclopædia Britannica, Ninth Edition, v. 13.djvu/324

 308 IRON of the shaft, so that they havo a tendency to fall over inwards during descent and produce intermixture ; in this way a much more nearly uniform degree of porosity of the whole mass (and conse quently of action of the ascending gases) is brought about than would be the case were the materials introduced through a narrow funnel so as to form a convex-surfaced heap in which the ore would accumulate in the centre. Sometimes the cup and cone arrange-- ment is modified by making the cone to rest upon the inner and lower edge of the hollow in the cup, so that the introduction of fuel is accomplished by raising the cone instead of lowering it, the object of this being to diminish the height of the furnace by the space through which the cone would otherwise sink when lowered. With this arrangement the mate rials run into the furnace in a direction sloping towards the centre instead of away from it, sliding inwards along the converg ing sides of the cup. To avoid the central accumulation of fuel and the lateral preponderance of &quot;burden&quot; (ore and flux) thus promoted, an inverted annular funnel is suspended underneath the lower oriiice of the cup, so that the falling substances im pinge upon this and slide off FIG. 27. Collecting Top. again with a motion towards the circumference of the shaft just as they do from the cone itself in the ordinary arrangement. Prior to the introduction of the cup and cone, a form of tunnel- head in which no valve or cone exists was employed, represented in fig. 27. A hollow annular chamber BB is built in the upper portion FIG. 28.- Langen s Collector Vertical Section. of the stack, communicating by arched cavities A, A, A with the shaft, and also with the exit gas main C ; a considerable fraction of the gases then passes out through the arched cavities when the materials are heaped up to the level of the charging door D. With small furnaces the wall between the shaft and the chamber B is made of FIG. 29. Langen s Collector Horizontal Section, oast or wrought iron ; in some cases the gas has been collected through a central tube in the axis of the shaft supported by groins springing from the shaft, the ore, &c., being charged through the annular opening between this tube and the shaft. Arrangements of this kind are still used in Sweden. In Coingt s gas collector the central tube is combined with a modification of the cup and cone arrangement. Langen s arrangement (figs. 28, 29) is a some what similar combination, the cone being made into a bell with perforated top, the edges of the perforation being turned over in wards bb ; the bell rests upon the cup aa, the turned over edge cc fitting into a water lute surrounding the central tube kkk, so that whilst the bell is lowered the furnace top is gastight or nearly so. By means of a pair of levers d, d and a counterpoise swung on a horizontal axle at r by means of a winch e, the bell can be raised so that the charge in the cup falls into the furnace, sliding down the inclined surface. Two safety valves x and fg are provided, the latter being ordinarily supported by the pressure of the gases, but falling by its own weight when the gas pressure is relieved by raising the bell, so as to close the top of the gas shaft, the turned-down edges of g fitting into the annular groove oo ; his a small manhole for the introduction of scrapers to clear out flue dust when required. Composition of Waste Gases. In general terms the escaping gases may be said to be the nitrogen of the blast mixed with variable proportions of carbon oxide and dioxide, and usually small quantities of free hydrogen ; when raw coal is the fuel, the proportion of hydrogen is greater, and carburetted hydrogens are also present. The main sources of hydrogen when coke and charcoal are used as fuel are probably the hydrogenous matter in the fuel, and the moisture contained in the blast and in the materials as water of hydration not expelled until they reach a part of the furnace sufficiently high to cause the water vapour to react whilst still nascent on the carbon present, forming carbon oxide and hydrogen (see 10). Various solid substances ore mechanically carried up with the gases, these having in many instances been vaporized at the lower levels, condensing again in the relatively cooler portions of the furnace as finely divided particles. This especially applies to zinc oxide (formed by the oxidation of zinc vapour generated by the re duction of zinc compounds in the ores) and to compounds of the alkali metals, and gives rise in the latter case to a destructive flux ing action upon the brick-work of the iipper portion of the furnace and to a complication in the chemical changes ensuing in the furnace ; for the solid floating particles are more or less intercepted and filtered out, as it were, from the ascending stream of gases by the materials in the upper part of the furnace, and are thus brought back again to the lower level, so that an accumulation in the furnace of alkali metals is produced which ultimately causes the actual quantity of alkaline compounds in the furnace to bear a very con siderable proportion to the iron present, although the amount of potash and soda in the ore flux and fluel is originally only trifling as compared with the iron. Those portions of the suspended solid matters which are not thus retained in the furnace by condensation on the materials are more or less deposited in the gas flues, and the heating stoves, &c., in which the gas is burnt, sometimes causing considerable inconvenience, and rendering it necessary to clean out the deposits from time to time. To avoid this clogging, the fume is sometimes washed out of the gases by jets of water in the form of spray before they pass on from the downcast pipe to the stoves ; an arrangement of this description applied to the Lucy fur nace (Pittsburg, U. S.) has worked well. The following analyses represent the composition of the fume deposited in the gas flues of various furnaces : Clarence. El. Brivet Furnaces Furnaces of Phoenix Iron Source of Fume] and Analyst. ..( Dowlais. Kiley. Soluble in Water. Insol uble in Water. Total. (Mouse). Xivoit and Ldtrange. ville, Penn sylvania. Blodgett Britton. Silica 30-33 1-37 11-00 12-37 0-56 3600 8-43 12-20 &amp;lt; 657 Ferric oxide 47-05 2-30 traces / 10-76 2-06 2-06 0-97 ) 21-72 3-98 Magnesia 1-13 traces 4-58 traces 13-28 traces 17-8G 81)10 0-69 2-84 Sulphuric anhy dride } 0-59 0-59 013 7-55 Chlorine 0-57 0-57 0-03 Potash and soda salts 2-16 2290 3-07 25-97 17-99 5-91 Carbonic anhy- }... 7-00 7-00 0-59 Water and nut ters lost on igni- - 0-03 1040 10-46 1-77 1-66 1-42 Po. phosphate 0-75 Li 0-38 (Phosphoric acid.) 09-27 52-G7 47-17 99 84 98-57 10000