Blast fur- 

 nace. 



308 



cess requiring more skill and management, it is proba- 

 ble that it would not be known so early as cast iron, and 

 the other metals more easily obtained. 



Malleable iron must have been known to man, long 

 before the methods of extracting it from its ores was 

 understood, as masses of native iron have been found 

 in various parts of the world, which we now supposed 

 to be of meteoric origin. 



In the manufacture of iron for the various purposes 

 to which it is applied, it is divided into three branches, 

 viz. cast or pig iron, malleable iron, and steel, the cast 

 iron being the first state in which it is produced from 

 the ore. We shall first describe the various processes 

 which it undergoes, from the roasting of the ore to its 

 being cast into pigs, in which state it is used for casting 

 into various articles by the irop founder, and also em- 

 ployed tor tlic manufacture of malleable iron. 



The rick iron ores of Sweden and" Russia, and the 

 Cumberland ore, are the most proper for making what 

 is called the forge pig iron, from its being the best 

 fitted for mailing malleable iron by the forge used for 

 that purpose. 



The poorer kinds of iron ore, which are the most 

 common in this country, and called iron stone, are more 

 fitted for making the casting metals employed in the 

 founderics. It owes this quality to its containing a great- 

 er portion of carbon than the forge pig. This depends 

 upon circumstances which we shall hereafter explain. 



In most of the rich ores of iron, particularly those of 

 Cumberland, the iron is combined with oxygen only ; 

 and when the oxygen is extracted, pure malleable iron 

 is the result. This change nas always been produced, 

 by heating the ores with charcoal till the iron became 

 fused. This fused mass, however, was never found to 

 be pure iron, but combined with more or less carbon, 

 to the presence of which it owes its fusibility. It was 

 formerly thought, that the change was effected upon the 

 oxide of iron, by the ore being first brought into a state 

 of fusion, in order that each particle of the oxide might 

 come in contact with the carbon, before the oxygen 

 could be detached from the iron. Subsequent experi- 

 ence, however, has shewn, that the whole of the oxygen 

 can be detached from a mass of the ore, without alter- 

 ing its form. The process by which this change is ef- 

 fected, is called cementation. It consists in stratifying 

 the ore in small masses with powdered charcoal, in a 

 close vessel, and exposing them to a bright red heat 

 for a length of- time, depending upon the size of the 

 pieces of ore. If the process be stopped at one particu- 

 lar point, the masses of ore, which were previously an 

 oxide of iron, will be found in the state of pure malle- 

 able iron, without any change of form or size. If the 

 process be kept up longer, they will combine with the 

 carbon, and first pass into the state of steel ; and with 

 still more carbon, will be converted into the state of 

 cast or pig iron. The same change is found to be pro- 

 duced in the poorer ores, in which the iron is sometimes 

 not more than 25 per cent, the rest being earthy mat- 

 ter, which requires to be brought into a state of fusion 

 before the iron can be developed, after the oxygen is sepa- 

 rated. It is the separation of this earthy matter from the 

 iron, after the oxide has been reduced by cementation, 

 which constitutes the most difficult part of the art of 

 smelting iron by the blast furnace. These preliminary 

 observations will enable us to conceive the nature of, 

 and lead us to the construction of the blast furnace, 

 from the changes it has to produce upon the ore. 



One part of the furnace has, first, to be occupied by the 

 ore and the carbonaceous matter, by which the oxide of 



IRON. 



iron in the iron-stone loses its oxygen, and afterwards Iron, 

 acquires as much carbon as tbg intended qualjty of the ^*~~Y~** 

 iron requires. After this is effected, tlie same furnace 

 in another part, with the assistance of somfe foreign mat- 

 ter, must be capable of giving a greater heat than that re- 

 quired for the cementation, by which the earthy matter 

 is separated, and the iron fused and collected in a re- 

 cess at the bottom of the furnace. These different parts 

 of the blast furnace we shall more particularly describe 

 in the plans and sections represented in Plate CCCXL. PLATE 

 Figs. 1, 2, 3, *, and 5, &c. A, Fig. 2, is the opening 01:0x1... 

 for the introduction of the materials. B the body of p ' s - *> ~' 

 the furnace, where the cementing process is carried on. 

 C the place where the blast is introduced, and it is a 

 little above this where the greatest heat is produced. 

 At this point the earthy matter is separated from the 

 iron, which earthy matter, uniting with the flux em- 

 ployed, is converted into a fusible cinder or scoria. The 

 iron being now fused, sinks down into the recess, or 

 trough D, while the liquid cinder floats upon the liquid 

 iron, defending it from the action of the blast. 



In smelting iron ore, a certain quantity of coke is em- 

 ployed. Part of this is to generate the heat necessary 

 to its reduction, and another portion combines with the 

 oxygen of the ore, and is deposited in the form of car- 

 bonic oxide. Besides this, a third portion combines 

 with reduced oxide, converting it into a carburet of 

 iron, which afterwards is cast into pig iron. The pro- 

 portions of coke to the iron ore, or iron stone, is more 

 or less dependent upon the quality of the iron to be 

 formed ; the richest and most highly carburetted iron, 

 commonly called No. 1. requiring the greatest propor- 

 tion of coal, while the inferior iron, such as is known 

 by the name of forge pig, requires the least coal. The 

 greater the proportion of the ore to the coal, the greater 

 is said to be the burden of the furnace. 



Besides the ore and the coke, a third substf.nce is al- Fluxing 

 ways found necessary, which has received the general matter, 

 name ofjlux. The quality of this substance varies with 

 the nature of the ore ; but limestone is commonly em- 

 ployed. The reason for this will be obvious, when it is 

 known that the earthy part of the greater proportion of 

 ores is clay, and that lime and clay, in certain propor- 

 tions, are very fusible ; while each of these earths, in a 

 separate and pure state, is not fusible in the hottest 

 furnace. Hence it is, that when the iron ore contains 

 lime instead of clay, which is sometimes the case, it is 

 found necessary to employ clay, or some argillaceous 

 substance as a flux. 



The proportion of the fluxing matter to the ore, is 

 in general determined by a number of trials with the 

 blast furuace itself; yet it must be allowed to be a very 

 expensive and unscientific method of proceeding. 



We have already on record, many facts relating to 

 the fusibility of compound earths, and if such facts 

 were yet to make out, a few experiments on a snlall 

 scale would be sufficient for their accomplishment. 

 This being ascertained previous to the commencement 

 of an iron work, it would next be necessary to make a 

 perfect analysis of the ore and the coal, with a view to 

 determine the proportions of their earthy matter, the 

 proportions of the ore to the coke being previously 

 known. The fluxing material now to be added to these, 

 must be such as to make the most fusible compound 

 with the earthy matter in the coke and ore. This know- 

 ledge will enable the iron master to commence his 

 work with the greatest chance of success, and the least 

 risk of unnecessary expence, which is very considerable 

 on the large scale of a blast furnace. 



