184 On the Employment qf'Jieated Air 



applied in some of the iron-works where this method of work- 

 ing the ore has been introduced. 



The air is blown by cylinder bellows in the usual manner, 

 but before entering the smelting furnace it passes through pipes 

 of cast-iron, heated to redness, which are altogether about thirty 

 feet in length, and three feet in diameter. They are usually 

 made in three or four pieces, joined together by apertures con- 

 siderably less than three feet in diameter, and placed horizon- 

 tally, or in whatever manner the local arrangements about 

 the furnace may render most convenient. A brick arch is 

 then thrown round the pipes, leaving a free space of about 

 eight inches and upwards between it and them, and two or 

 more furnaces constructed, so as to heat the pipes in the 

 archway, the flues playing into it, and terminating in a com- 

 mon vent at the farther extremity. They may be considered, 

 therefore, as placed on the floor of a long and narrow rever- 

 beratory furnace, about six feet high, and nearly of the same 

 breadth, being at the same time protected by fire bricks when 

 they might be injured by the direct flame of the furnaces. 



The iron-ore is smelted according to this plan with little more 

 than half the coal necessary when the furnaces are worked with 

 air in the usual manner ; the small coal which is sold at an in- 

 ferior price is found quite sufficient for heating the pipes. 



It has also been ascertained, that there is no difficulty in 

 smelting the iron ore with common coal instead of coke, and in 

 some furnaces at present in use, no coke whatever is employed, 

 so that it is probable the trouble and expense attending its pre- 

 paration will be unnecessary. It is likewise in contemplation 

 to endeavour to reduce the iron-ore at once in the furnace, with- 

 out any previous calcination, and the proprietors of some of the 

 iron-works seem to entertain little doubt that they will be suc- 

 cessful in their attempt. 



The great effect produced by the heated air in these furnaces 

 must be attributed to the circumstance that, according to this 

 plan, a higher temperature can be more easily excited and 

 maintained, than when the blast is supplied with air at the ordi- 

 nary temperature of the atmosphere. And the great saving of 

 fuel we would presume does not arise from a greater quantity 

 of heat being evolved from a giren quantity of coke or coal in 



