144 



IRON. 



of this quantity of metal, there is required seven 

 tons of coke, eight tons of roasted iron stone, and 

 three and three-eighths tons limestone as a flux. 

 According to a later writer on the iron manufacture, 

 one of the large furnaces in Wales receives on an 

 average, fifty charges in twelve hours. Each charge 

 requires six cwt. of roasted ore, in all amounting to 

 fifteen tons produced from eighteen tons of raw 

 mine. The same quantity of coke is required, i. e. 

 fifteen tons produced from about twenty-two and a 

 half cwt. of coals. The limestone required, is six 

 tons, so that the whole weight of the charges for 

 twelve hours, is thirty-six tons, from which only six 

 tons of cast iron are produced. From this, we may 

 estimate the loss of material in roasting, coking and 

 smelting for two runs which occupies twenty-four 

 hours . 



Coal*. . . . 



Mine, . 

 Limestone, . . 



Whole weight, 

 Supplied to the furnace, 

 Iron produced . . 



57 tons. 



M 



12 



lor, 



72, loss, . 33 tons 

 . 12, loss, . 60 



Total loss, 93 tons. 



Iii England and everywhere, else until very recently, 

 it was supposed, that the colder the air was injected 

 into the furnace the better; and the two currents on 

 entering the furnace chilled the materials much, 

 and produced a sort of pipe or channel in the melted 

 metal, which opposed its entrance. These pipes 

 often extended so as nearly to meet in the middle of 

 the furnace. The keeper watched the state of these 

 pipes, and regulated the blast, so that they should 

 neither be too long nor too short. These pipes, 

 tended to prevent the blast pipe, as well as the cast 

 iron lining of the wall, through which they were led, 

 from melting. 



Mr J. B. Neilson, civil Engineer and manager 

 of the Gas Works of Glasgow, had, in the course of 

 the year 1824, directed his attention to blast fur- 

 naces, in consequence of some inquiries having been 

 made, if he could devise any means of purifying the 

 air propelled by the blowing engine before it reached 

 the furnace ; in any way similar to that in which 

 coal gas is purified. The inquirer suspected 

 that it was the presence of the sulphurous vapour, 

 that injured the air of the blast, seeing that furnaces 

 commonly wrought worst in the summer months. 

 But experience led Mr Neilson to attribute the 

 evil to another cause. From some simple experi- 

 ments, he concluded, that by heating the air before 

 it went into the furnace, he could effectually remove 

 the evil under consideration. It is known that air 

 will not support combustion until heated to a tem- 

 perature of 1000 Fahrenheit, and therefore until it 

 acquires that temperature, by coming into contact 

 with the heated mass of the fire, it must act prejudi- 

 cially: from which it is manifest, that the nearer it can 

 be brought to that point before entering the fire, the 

 better ; yet all things considered, there may be a 

 certain temperature at which the effect of the blast 

 will be a maximum. The temperature originally 

 employed by the patentee was, we believe, about 300 

 and this was the heat of the blast at Clyde iron works 

 in 1830, when coke was employed. The advantage 

 obtained by the employment of the hot blast at this 

 temperature will at once appear from the fact, that 

 during the first six months of the year 1829, when 

 all the furnaces at Clyde iron works, were wrought 

 with the cold blast, 8 tons l cwt. of coal, converted 

 into coke, were required for the smelting of one ton of 

 cast iron, but during the first six months of 1830, 

 when the blast was heated to about 300, the same 

 quantity of iron required only 5 tons 3 cwt. of coals 

 converted into coke, which after deducting 8 cwt. of 



coal employed in heating the air gives a saving of 

 2 tons 10 cwt. The success of the hot blast, at a 

 temperature of 300 induced the iron manufacturers, 

 to try it at a still higher temperature, and the results 

 proved proportionally beneficial. In the course of 

 the year 1831, the temperature of the blast was 

 doubled, so that it was not less than 600, and the 

 success was such, that they were induced to employ 

 coal instead of coke in the smelting furnace, which 

 induced a saving to a very considerable amount. In 

 1829, 8 tons IJ'cwt. of coal were required for coke to 

 smelt one ton of iron, whereas in 1833, only 2 tons 

 13i cwt. of coals, not converted into coke, were re- 

 quired for the same purpose. The increase of com- 

 bustion with the blast at 600, precludes the neces- 

 sity of coking before smelting, for the intense heat of 

 the blast is sufficient to compensate for the great 

 quantity of latent heat that must arise with the va- 

 pours expelled from the coals during combustion. 



The patentee does not confine himself to any par- 

 ticular mode of heating the pipes, nor the temperature 

 of the air. In some cases the pipes have been 

 heated by the smelting furnace itself, and in others, 

 by a separate furnace, which latter mode would ap- 

 pear to be the most economical. 



We will here lay before the reader, a description 

 of furnaces heated in both ways, which with some 

 modifications, we have drawn up, from a very valu- 

 able French work entitled Portefeuille Industrial, now 

 (Jan. 1836), in the course of publication at Paris. 



The annexed cut represents the first form of 

 the air-heating apparatus, invented by Mr Neilson, 

 where a separate fire is used. 

 Fig. 2. 



The heating apparatus is contained within a kiln or 

 furnace, F F', constructed of brick. Within this 

 kiln two straight tubes, ABA' B', are laid 

 horizontal and parallel to each other. In the upper 

 surface of each of these large pipes, circular 

 openings, C C' are made for the reception of the 

 ends of small bent tubes. These tubes which are 

 seen at S S' are bent so as to form arcs of circles, 

 the length of each arc being more than the semi-cir 

 cumference. They stretch across the kiln, one extrem 

 ity terminating in each of the long pipes, A B A'B' 



Fig. 3. 



