Before proceeding to describe the manufacture of iron, we give two analyses of British ores: the first is by Mr. J. Spiller, taken from a series published in the _Memoirs of the Geological Survey, and the second is by Dr. Murray Thomson.
It will be noticed that in the case of these ores the impurities are rather numerous. Nevertheless, the modes of preparing and smelting them are soniewLat rude and simple, as the low price of iron -will not permit of its ores being treated with the same care as the ores of lead, copper, tin, and some other metals.
Iron ore is still reduced in the s. of Europe by the old and imperfect process of the Catalan forge, not unlike a common smith's forge. In Great Britain, however, as well as in all other countries where iron is largely smelted, the blast-furnace is now universally employed, by means of which the metal is obtained in the state of crude or cast iron. For the finer kinds of iron, charcoal is the fuel employed. because, unlike coal or coke, it contains no sulphuret of iron or other injurious ingredients, The Rus sian and Swedish furnaces smelt with charcoal, and on this, as much as on their pure ores, depends the high reputation of their iron. A solitary charcoal-furnace at Ulver stone in England, and another at Lorn in Scotland, are still working—the only relics of times past, when this was the only fuel employed.
As a preliminary process to the actual smelting in the blast-furnace, clay and black band ironstones are generally roasted. This is accomplished by breaking the ore ipW small pieces, spreading it in open heaps on the ground, and mingling it more or less with small coal according to the nature of the ore. .13iackband commonly contains enough of carbonaceous matter to burn without the addition of coal. The pile, which may contain from one to several thousand tons of ore, is lighted at, the windward end, and burns gradually along, aided by occasional fires in the sides, till the whole heap has undergone calcination, the time required for this purpose being generally about a month. Some times the operation of roasting is performed in close kilns, instead of open heaps, a mode by which the ore is considered to be more uniformly rossted,•and with considerably less fuel. Of the kilns are often heated by the waste gases of the blast-furnace. By calcination, clay ironstone loses from 25 to 30, and blackband from 40 to 50 per cent of its weight, the loss consisting chiefly of carbonic acid and water, but sulphur and other volatile substances are also dissipated in the process. The roasting also converts
the protoxide and carbonate of iron into peroxide, which prevents the formation of sings of silicate of iron, such slags, owing to the difficulty of reducing them, causing a loss of iron. In this country rich ores like the magnetic or red hematite are not subjected to calcination, but they are so in Sweden.
The older type of blast-furnace consists of a massive tower of stone or brick-work strengthened with iron binders; the newer plan is to build it of comparatively thin brick work, and surround it entirely with strong iron plates. In either case an inner lining of refractory fire-brick is given to it, which is separated from the 'outer portion of the wall by a narrow space filled with sand, Internally they vary much in form, but per. haps the barrel shape is the most prevalent, and most of them contract towards the bot tom in the shape of an inverted cone. Recent ones have been built from 80 to 100 ft. in height, instead of not more than GO as formerly. The blast-pipe, with its tuyere branches, surrounds the hearth, and on one side there is a recess and openings for run nine off the metal and slag. See BLAST-FURNACE.
Firs 1 is a sectional view of a hot blast-furnace, with the blowing-engine and other • 0.
appliances, which is taken, with some modification, from Mr. Fairbairn's work on iron.
It may be well to state here that one engine usually supplies the blast to several fur naces. A is the body of furnace; B the hearth, above which are placed the tuyeres, C; D is the bell and cone arrangement, around which there is a gangway to enable the workmen to feed the furnace. The blowing-engine is shown at F. Air is forced into the furnace by means of the blowing cylinder, G, from which it passes into the receiver, 'a, and thence along a pipe into the heating-oven. T. Here a large surface of pipe is exposed, in arch-shaped rows, to the fire, which heats the inclosed air to from 600° to 1000' F. At some temperature within this range it enters the lower part of the furnace by means of the tuyeret, C. Some of the larger blowing-engines discharge 60,000 cubic ft. of air per minute, under a pressure of 31 lbs. per sq. inch. See BLOWING-MA CHINES.