IRON. 



147 



short extract from a very valuable paper, on the hot | 

 blast by Dr Clark, of Aberdeen, which was read 

 before the Philosophical Society of Edinburgh in 

 March of the year 1835. 



"As nearly as may be, a furnace, as wrought 

 at Clyde Iron works in 1833, had two tons of 

 solid materials an hour put in at the top, and this 

 supply of two tons an hour was continued for twenty 

 hours a day, one half hour every morning, and ano- 

 ther every evening, being consumed in letting off the 

 iron made. But the gaseous material the hot air 

 what might be the weight of it ? This can easily be 

 ascertained thus : I find, by comparing the quantities 

 of air consumed at Clyde Iron works, and at Calder 

 Iron works, that one furnace requires of hot air from 

 2500 to 3000 cubical feet in a minute. I shall here 

 assume 2867 cubical feet to be the quantity; a 

 number that I adopt for the sake of simplicity, inas- 

 much as, calculated at an avoirdupois ounce and a 

 quarter, which is the weight of a cubical foot of air 

 at 50 Q Fahrenheit, these feet correspond precisely 

 with two cwt. of air a minute, or six tons an hour. 

 Two tons of sol id material an hour, put in at the top 

 of the furnace, can scarce hurtfully affect the tem- 

 perature of the furnace, at least in the hottest part of 

 it, whicli must be far down, and where the iron, 

 besides being reduced to the state of metal, is melted, 

 and the slag too produced. When the fuel put in at 

 the top is coal, I have no doubt that, before it comes 

 to this far-down part of the furnace the place of its 

 useful activity the coal has been entirely coked ; so 

 that, in regard to the fuel, the new process differs 

 from the old much more in appearance than in essence 

 and reality. But if two tons of solid material an 

 hour, put in at the top, are not likely to affect the 

 temperature of the hottest part of the furnace, can 

 we say the same of six tons of air an hour, forced in 

 at the bottom near the hottest part? The air sup- 

 plied is intended, no doubt, and answers to support 

 the combustion ; but this beneficial effect is, in the 

 case of the cold blast, incidentally counteracted by 

 the cooling power of six tons of air an hour, or two 

 cwt. a minute, which, when forced in at the ordinary 

 temperature of the air, cannot be conceived otherwise 

 than as a prodigious refrigeratory passing through 

 the hottest part of the furnace, and repressing its tem- 

 perature. The expedient of previously heating the 

 blast obviously removes this refrigeratory, leaving 

 the air to act in promoting combustion, without 

 robbing the combustion of any portion of the heat it 

 produces." 



Dr Clark concludes his paper by the following 

 statements regarding the Clyde Iron works : 



The Blowing-engine has a steam cylinder of forty 

 inches diameter, and a blowing cylinder of eight feet 

 deep and eighty inches diameter, and goes eighteen 

 strokes a minute. The whole power of the engine 

 was exerted in blowing the three furnaces, as well as 

 in blowing four, and in other cases there were two 

 tweers of three inches diameter to each furnace. 

 The pressure of the blast was two and a half Ibs. to 

 the square inch. The fourth furnace was put into 

 operation after the water tweers was introduced, and 

 the open spaces round the blowpipes were closed up 

 by luting. The engine then went less than eighteen 

 strokes a minute in consequence of the too great re- 

 sistance of the materials contained in the three fur- 

 naces to the blast in its passage upwards. 

 Materials constituting a Charge. 



1829, 



1830, 



Coke, 



Roasted Ironstone, 



Limestone, 



Coke, 



Roasted Ironstone, 



Limestone, . 



cwt. qrs. Ib. 

 400 

 3 1 14 



3 10 

 500 

 500 



1 1 |o 



1833, 



Coal, . 



Roasted Ironstone, 



Limestone, . 



cwt. qrs. Ili 

 (i 00 

 500 

 1 



An impression has gone abroad among founders 

 and machine makers, that the iron produced in the 

 hot blast furnace, is inferior in quality to that pro- 

 duced in the cold blast furnace ; but correct experi- 

 ments have, we believe, not yet been performed on 

 the subject. It ought not to be forgotten, that the 

 iron produced by the same furnace, is different at 

 different times, and there is very frequenlly a differ- 

 ence of quality in the iron of one smelting. 



The quality of metal issuing from the smelting fur- 

 nace, will vary with the quantity of carbon it con- 

 tains. The quantity of carbon will depend, in a 

 great measure, upon the quantity of charcoal, coke, 

 or coal that has been employed in smelting the ore; 

 and the appearance of the metal, as it flows from the 

 tap hole, will indicate the state of the metal. On 

 the surface of the liquid metal, there floats a sub- 

 stance, called by the workmen kish, which has the 

 shining appearance of plumbago, and the presence 

 of this substance, indicates that the metal is saturated 

 with carbon ; and if great in quantity, the iron maker 

 immediately takes the hint to diminish, proportion- 

 ally, the quantity of the ore. The appearance of the 

 cinder, is likewise a good guide, for when it assumes 

 a greenish-yellow colour, it is a proof, that from the 

 want of carbonaceous matter, some of the oxide of 

 iron has not been decomposed. When the oxide of 

 iron is in great excess, the cinder appears of a black- 

 ish-green colour. The nature of the iron produced 

 will vary, as before observed, with the manner in 

 which it has been smelted. Some conduct the pro- 

 cess in such a way, as to produce iron for the foundery, 

 and others, so as to produce iron for the forge, this 

 latter containing less carbon than the former. The 

 carbon is more abundant in the iron, in proportion as 

 it is soft and tough ; and there is this remarkable 

 circumstance in pig and bar iron, or iron for the 

 foundery, and iron for the forge ; that the nearer they 

 approach each other in appearance and mechanical 

 properties, the greater is the difference of their 

 chemical composition, at least, so far as carbon is 

 concerned. We cannot enlarge on the distinctions of 

 iron, in this place, to any greater length, but refer 

 the reader to that section of this article, which treats 

 of the chemical properties. 



The first step in the process of converting cast or 

 pig iron, into bars of malleable iron, is refining. The 

 pigs from the smelting furnace, are placed along with 

 coke, in a smaller furnace supplied with the blasts 

 from the blowing-engine. The coke and pigs are 

 placed in a trough, whose sides are formed of cast- 

 iron plates, but the bottom is of masonry ; this 

 trough is surrounded by a sort of canal, in which cold 

 water is kept constantly running. There is a tap hole 

 at one side of the trough, which opens into a rectan- 

 gular mould at the side of the furnace, which mould is 

 commonly about twenty feet long, and two broad, 

 into which the metal is allowed to run after it has 

 been refined. This mould is likewise surrounded 

 with cold water, as also the blast pipes. The material 

 is set on fire, and the blast kept up until the pig-iron 

 is brought to a state of fusion. The metal is kept in 

 a state of fusion for at least two hours, after which it 

 is run off into the mould, deprived of a great quantity 

 of its carbon, or as the name of the process implies, 

 refined. The furnace is constructed of such dimension 

 as to yield about a ton of refined metal at each tap- 

 ping ; and it may be stated that the loss of weight 

 by the process, is usually about ten per cent. The 

 sheet of metal whicli fills the mould to the depth of 

 about two inches, is next withdrawn, and broken 

 K 2 



