144 



THE CIVIL ENGINEER AND ARCHITECT'S JOURNAL. 



[May, 



The modern science of medijEval arcliitectore is at present an immature sci- 

 ence ; every day is adding to our stock of knowledge or correcting false 

 impressions. It is not many years since Hickman introduced the classifica- 

 tion and nomenclature of the difl'erent styles now in use. How is it possible 

 •lien that in so brief a period «e can hare learned all of the science that is 

 worth knowing — that we have now learned so much that we may venture 

 to correct the errors of our teachers, the medixval architects? At least, 

 there is no harm iu wailing awhile till we be quite sure that our corrections 

 are not the result of imperfect knowledge. 



Of this there will be no debate, that no mischief can arise from confining 

 our endeavours, fur the present, to careful reparation. The removal of 

 Hat plaster ceilings, of Grecian or Elizabethan screens, of the defilements 

 of stucco, paint and whitewash, and the other inventions of churchwardens 

 and parish architects, are works that may be undertaken without the 

 chance of their propriety being hereafter disputed. Add to these, the 

 repair of parts which have decayed by process of time or been mutilated 

 by violence, the restitution of adornments where clear traces of them re- 

 main, and the scniiiulous preservation of every portion of the genuine meduE- 

 ral architecture, and we have done all that the present, or, probably, any 

 future, state of our knowledge can justify. 



BLAST FURNACE. 



Observations on the more recent lieaearches concerning the Operation) of the 

 Blast Furnace in the manufacture of Iron. 



By Dr. J. L. Smith. 



[From Silliman't Journal for March, 1846.] 



The great difference existing between metallurgical operations of the pre- 

 sent day, and those of a former period, is owing chiefly to the ameliorations 

 produced by the application of the science of chemistry to the modus operandi 

 of the various changes taking place during the operations, from their com- 

 mencement to their termination. 



Copper and some other metals are row made to assume forms in the che- 

 mist's laboratory, that formerly required great artistical skill for their pro- 

 duction — the chemist simply making use of such agents and forces as are at 

 his command, and over which he has, by close analytical study, acquired 

 perfect control. Our object, at present, is only to advert to the chemical 

 investigations more recently made on the manufacture of iron, treating of 

 those changes that occur in the ore, coal, and flux, that are thrown in at the 

 mouth of the furnace, and in the air thrown in from below. For most that 

 ■will be said on this subject, we are principally indebted to the recent inte- 

 resting researches of M. Ebelman. 



The importance of a knowledge of the facts to be brought forward in this 

 article, will be apparent to every one in any way acquainted with the manu- 

 of iron. It will be seen, tliat the time is not far distant when the economy 

 in the article of fuel will amount in value to the present profit of many of 

 the works. The consequence must be, that many of those works that are 

 abandoned will be resumed, and others erected in localities formerly thought 

 unfit. 



It is well known that the blast furnace is the first into which the ore is in- 

 troduced, for the purpose of converting it into malleable iron, and much 

 therefore depends upon the state in which the pig metal passes from this 

 furnace, whether subsequent operations will furnish an iron of the first 

 quality or not. 



In putting the blast furnace into operation, the first step is to heat it for 

 acme time with coal only. After the furnace has arrived at a proper tempe- 

 rature, ore, fuel and flux, are thrown in alternately, in small quantities, so as 

 to have the three ingredients properly mixed in their descent. In from 25 

 to 48 hours from the time when the ore is first thrown in, the entire capacity 

 of the furnace, from the tujer to the mouth, is occupied with the ore, fuel, 

 and flux, in their various stages of transformation. 



In order to explain clearly, and in as short a space as possible, what these 

 transformations are, and how they are brought about, we may consider : — 1. 

 The changes that take place in the descending mass, composed of ore, fuel, 

 and flux. — 2. The changes that take place in the ascending mass, composed 

 of air and its hygrometric moisture, thrown in at the tuyer. — 3. The chemical 

 action going on between the ascending and descending masses. — 4. The 

 composition of the gases in various parts of the furnace during its operation. 

 — 5. The causes that render necessary the great heat of the blast furnace. 



1. Changes that take place in the descending mass, composed of ore, coal, 

 and flux. — By coal is here meant charcoal ; when any other species of fuel 

 is alluded to, it will be specified. In the upper half of the fire-room, the 

 materials are subjected to a comparatively low temperature, and they lose 

 only the moisture, volatile matter, hydrogen, and carbonic acid, that they 

 may contain ; this change taking place principally iu the lower part of the 

 npper half of the fire-room. 



In the lower half of the fire-room, the ore is the only material that under- 

 goes a change, it being converted wholly or ia part into iron or magnetic 



oxide of iron — the coal is not altered, no consumption of it taking place 

 from the mouth down to the commencement of the boshes. 



From the commencement of the boshes down to the tuyer, the redaction 

 of the ore is completed. Very little of the coal is consumed betweeu the 

 boshes and in the upper part of the hearth ; the principal consumption ol it 

 taking place in the immediate neighbourhood of the tuyer. 



The fusion of the iron and slag occurs at a short distance above the tuyer, 

 and it is in the hearth of the furnace that the iron combines with a ])ortion 

 of the coal to form the fusible carburet or pig-iron. It is also on ihe hearth 

 that the flux combines with the siliceous and other impurities of the ore. 

 This concludes the changes which the ore, coal, and flux undergo from the 

 mouth of the furnace to the tuyer. 



If the fuel used be wood, or partly wood, it is during its passage thronuh 

 the upper half of the fire-room that itsvolaiile jiarts are lost, and it becomes 

 converted into charcoal. M. Ebelman ascertained that wood, at the deplli 

 of ten feet, in a fire-room twenty-six feet high, preserved its appearance alter 

 an exposure for 1| of an hour, and that the mineral mixed with it jireserved 

 its moisture at this depth; but three and a half feet lower, an exiinsure o( 

 3J hours reduced the wood to perfect charcoal, and the ore to iiiiignetre 

 oxide. The temperature of the upper half of the fire-room, when wood » 

 used, is lower than in the case of charcoal, from the great amount of heal 

 made latent by the vapour aiising from the wood. In the case of bitumiiiouj 

 coal, liunsen and Playfair find that it has to descend still lower before it is 

 perfectly coked. 



After the wood is completely charred, or the coal become coked, the sub- 

 sequent changes are tlie same that happen in the charcoal furnaces. 



2. Changes that take place in the ascending mass, vhich is composed of air 

 and hijgrometric moisture. — The weight of the air thrown in at the tuyer ia 

 twenty-four hours is twice that of the ore, coal, and flux, thrown in at the 

 mouth during the same lime. 



The air, as soon as it enters the tuyer and reaches the first portion of coal, 

 undergoes a change — its oxygen is converted into carbonic acid, and its 

 moisture decomposed, furnishing hydrogen and carbonic oxide — after as- 

 cending a short distance (12 or 18 inches,) the carbonic acid is converted 

 into carbonic oxide — between this point and the upper part of the ho»hes it 

 undergoes but very little change, having added to it a further small amount 

 of carbonic oxide. So the ascending column at the top of the boshes » 

 composed of nitrogen, carbonic oxide and hydrogen — from this point it t>6- 

 gins to undergo a change ; the carbonic oxide diminishes, carbonic acid ap- 

 pears, and goes on increasing for about half the way up the fire-room ; after 

 which the carbonic acid, carbonic oxide, and nitrogen remain the same, 

 when the hydrogen increases, and moisture begins to appear and augment 

 up to the mouth. The ascending mass, as it passes out of the mouth, con- 

 tains the vapour of water, carbonic acid, carbonic oxide, hydrogen, and nitro- 

 gen. The nitrogen undergoes no alteration in its passage through the fur- 

 nace, and the same is true of the hydrogen formed at the tuyer. 



If wood be used, the gases passing out of the mouth are the same as tliose 

 just mentioned, with an increased quantity of moisture, and the addition of 

 those pyroligneous products arising from the dry distillation of wood. 



In case of the use of bituminous coal, the gases, first alluded to, have 

 added to them ammonia, light carburetted hydrogen, olefiant gas,carbuietted 

 hydrogen of unknown composition, and sulphuretted hydrogen. 



3. rite chemical reaction occurring between the ascending and descending 

 masses. — From the foregoing statements we can at a glance see what are tU« 

 materials to be met with in the dill'erent parts of the furnace, and can there- 

 fore readily study their reactions upon each other. 



In the upper half of the fire-room little or no chemical action is taking 

 place, the ore, flux, and coal, as already stated, simply losing their volatili 

 parts. In the bottom of the upper half and the entire lower half of the firs- 

 room a reaction is taking place between the ore and the carbonic oxide of 

 the ascending column ; iron or magnetic oxide of iron and carbonic acid 

 being the result. It must be borne in mind that the coal has played no pari 

 in this reduction down to the commencement of the boshes, lietween the 

 boshes, and in the hearth, no reaction appears to take place between the 

 ascending and descending masses, but the reduction of the ore is completed 

 by the direct action of the coal upon the remaining portion of the undecom- 

 posed ore ; carbonic oxide being formed ; — and here is the first consumption 

 of the coal in its passage downwards. 



According to M. Ebelman, the ore loses in the fire-room fs of its oxygen 

 by the reaction of the oxide of carbon, and the remaining -/^ disappears in 

 the boshes and hearth, in the manner already stated, at the expense of from 

 T^ to ~ffj of the entire amount of charcoal used. 



The ore being now completely reduced, unites with a portion of carbon in 

 the hearth, melts at about 13 inches from the tuyer, and descends into tlw 

 crucible ; and here also the flux, combining with the impurities of the ore, 

 forms the slag, which melts. 



The coal and the air react upon each other most powerfully, just in the 

 neighbourhood of the tuyer, where the most intense beat is produced ; tbs 

 oxygen becomes converted into ( arbonic acid, which acting upon a portion 

 of the ignited coal, is almost at the same moment reduced to carbonic oxide; 

 the moisture of air acting on the ignited charcoal undergoes the decomposi- 

 tion already mentioned, hydrogen and carbonic oxide resulting therefrom. 



When the ore is easy of reduction, the gas at the boshes is represented by 

 100 nitrogen and 52-d carbonic oxide, ;)/«« the quantity of carbonic oxide 

 and hydrogen afforded by the moisture. 



It must be clearly understood, that these rules d« not apply to eiery 



