3/2 



I R O K. 



Iron. 



cause alone, would- be nearly -Jib upon an inch. Or, in 

 oilier words, if the air were introduced into the fur- 

 nace at 60", the same quantity would be admitted with 

 Alb less pressure upon an inch than if it were <)0". 

 Hence any means of cooling the air after its condensa- 

 tion, in .'.11 .-i-::sons of the year, must be attended with 

 beneficial consequences. If the air vault were made of 

 wrought iron, and its surface constantly kept wet, the 

 evaporation from so great a surface, if freely exposed on 

 all sides to the air, woidd cool the air very considerably. 

 Indeed, without the aid of the moisture, the effect would 

 be such as to recommend its adoption. In the summer 

 season there would be some advantage in bringing the 

 air under ground for a considerable distance before it 

 enters the blowing machine ; the reason for this will 

 be obvious, from the earth being colder than the air. 

 In the winter season, wlien the jarth is warmer than 

 the air, the supply should be from the atmosphere. 



The increased temperature of the atmosphere in the 

 summer, is the cause of another evil besides the increa- 

 sed volume of the air. The moisture necessarily ac- 

 companying it, is found to have a bad effect upon the 

 furnace, which has been more especially ascertained 

 by the use of the water-regulator, before alluded to. 

 The quantity of water in the atmosphere at any time, 

 depends upon the temperature, and the quantity of 

 moisture prevailing on the earth's surface ; so that the 

 temperature does not always indicate the quantity of 

 moisture which exists with the air. The most infalli- 

 ble method of finding the quantity of water in a cubic 

 foot of space, is by taking the dew point, or that poinf 

 of temperature when dew ceases to form upon the 

 surface of a body which has been allowed to remain 

 exposed in it for that purpose. The temperature of 

 this body, for instance a bottle of cold water, will be 

 the dew point. When a given space is saturated with 

 moisture, at 70, every cubic foot contains 4.53 grains 

 of water ; and the same space, at 50, contains 2.36 

 grains. Hence, if the air at 70* could, by passing 

 through a culvert in the earth, be reduced from 70 to 

 50, 2.17 grains of water would be deposited from each 

 cubic foot of air. This advantage, added to that arising 

 from its diminished volume above mentioned, will, in 

 a great measure, explain the difference in the quantity 

 of iron made in winter and summer. 



We shall conclude this department of iron manufac- 

 ture, by a more particular reference to the plate exhi- 

 biting the different parts of the blast furnace. 



Plate CCCXL. Fig. 1. is a section of the blast fur- 

 nace, showing the interior of the furnace from the top 

 to the bottom, and the part where the blast is introdu- 

 ced. The dark stripes which appear on the walls, are 

 vent flues for the escape of moisture, which would not get 

 off from such a massive building without injuring the 

 walls, when the heat is applied to the interior. Fig. 3. is 

 a plan at the level a a, Fig. 1. and 2, and PP, Fig. 1. a 

 plan at the part to which it joins. The light-shaded 

 squares are pillars of brick, constituting a false bottom, 

 on which the hearth rests, the cavities underneath being 

 for the escape of vapour, at the appertures m and n in 



Figs. 4, S. Figs. 4. and 5. Figure 4. is a plan across the aper- 

 ture where the blait is introduced, in which the blast- 

 pipes are seen. Although we have not before alluded 

 to two pipes, we now observe, that it is only some- 

 times resorted to, the single pipe being much more 



Fig. 2. common. Fig. 2. is a section elevation, at rjght angles 

 to the former one, Fig. 1. showing the satne interior 

 surface and the dam-stone d, over which the cinder 



P, 



l.ATE 



CCCXL. 

 Fig. 1. 



Fig. 3. 



flows, while the metal is retained by the dam, till it is : 

 let out at a hole v, on a ^evel with the bottom of the ^""".'"^ 

 n-i-i-f-i. T i- r.ViVil the: tyntp-stones, ami f-iriiri a bridge !'r.,vn: 

 over the cavity in wliich the HquidScinder' rises, t is CCi *-l- 

 the fillip-plate, to give the stone greater firmness, as e is 

 to the dam-stone, which is called the dam-plate. Seethe 

 tymp plate and dam plate, more particularly Figs. 6. Figs. C, 7 

 7. and 8. Fig. 5. is a plan at the bottom of the recess D, 8 - 

 showing the vent flues in the piers, and the hole j;for t'.ie 

 outlet of the metal, seen also in the dam-stone, Figs. 9. v . 

 and 10. Fig. 11. is a side view of the large crow, jj ss ' 

 in which the blast-pipe is inserted. The end of this 

 iron is defended, from the immediate action of the fire, 

 by covering it from time to time with, stiff fire clay. 

 Fig. 15, an end view of the same. Figs. 12, 13, 11, Figs. 12, 1 

 are different nose-pipes to fit the blast pipe. 14, 1 j. ' 



Manufacture of Bar Iron. 



All the varieties of pig-iron contain more or less of Manufac. 

 carbon, to which they owe their fusibility, which, in ture oi ba 

 all the varieties yet made, are fusible in proportion to iron -' 

 the quantity of carbon which they contain. In the 

 earlier stages of pig-iron manufacture, an opinion pre- 

 vailed that some varieties contained oxygen. Nothing 

 could be more absurd than this idea. Experience has 

 shewn, that all varieties contain carbon, else they would 

 not be fusible. And it will appear to any one acquaint- 

 ed with the laws of affinity, that carbon and oxygen are 

 incompatible in a mass of liquid matter, as they must 

 unite, and form an elastic fluid, till one or the other 

 would be exhausted. It is this kind of pig-iroiv, con- 

 taining the least carbon, which has been called oxygen- 

 ated, and also forge-pig, because it has been found the 

 best fitted for making bar or forge iron. It had long 

 been suspected, that malleable iron was no other than 

 the pig-iron divested of its carbon, but the idea was 

 not fully confirmed, till malleable iron was directly 

 formed by cementing the carburet, or pig iron, with a 

 substance which carried off its carbon without changing 

 its form. This can be effected in small castings of pig- 

 iron by the following process : Stratify alternately in 

 a crucible the cast metal articles with powdered iron- 

 stone (which contains an oxide of iron) in a close ves- 

 sel, and let the vessel be -covered by a lid very nearly 

 air tight. Expose the \vhole to a strong red heat for 

 ten or twelve hours, proportionate to the thickness of 

 the castings. When the mass is cold, take out the 

 pieces. If the change is complete, the pieces will bend 

 and work with the hammer when hot, possessing all 

 the properties of malleable iron. If, instead of the 

 castings, some cast iron borings be stratified with small 

 masses of the Cumberland iron ore, about the size of 

 small peas, and treated like the last, the bits of ore will 

 be found to be malleable. 



In both experiments, the oxygen of the oxide com- 

 bines with the carbon of the carburet, which escapes in 

 the form of carbonic oxide gas, leaving, if the-oxygi'n 

 and carbon be in proper proportions, pure iron behind. 



Although this process appears the most direct and 

 simple way of converting pig into malleable iron, the 

 process at present employed is essentially different, and 

 attended with very considerable waste. The method 

 used by the ancients was still less scientific, and is still 

 practised on the continent. It consists in laying the 

 .pigs of iron upon a hearth similar to a smith's tbrge, 

 surrounding them with charcoal, and blowing the fire 

 with bellows. The metal first melts, and is continual- 

 ly agitated with a rake, while it is exposed to the blast. 



