116 
Iron . 
cavity of the furnace which is of a conical figure, thirty 
feet high, and three feet diameter at the top ; from this 
part it enlarges into a funnel shaped chimney about eight 
feet high and sixteen in diameter at its mouth. The li- 
ning from the hearth to the top of the boshes is composed 
of large blocks of quartz grit, and that of the cavity of the 
furnace is formed of lire bricks 13 inches long, and three 
inches thick. About two feet above the hearth is a round 
aperture called the Tuyere , (Tweer) made in one of the 
sides of the crucible to admit the extremity of the blast 
pipe, through which the air in a high state of compression 
is forced into the furnace ; and at the bottom of the crucible 
is an aperture through which the scoriae and melted me- 
tal are from time to time discharged. A furnace of this 
construction, if it meets with no accident, may be kept in 
constant work for three years or more, without requiring 
any repairs. 
The furnace is charged at the chimney by regular inters 
vals with coak, iron ore, and limestone in the proportion 
of about 4 of the first, 3 1=3 of the second, and 1 of the 
third, by weight, care being taken so to regulate the fre^ 
qiiency of the charges, as that the furnace shall be always 
full nearly to the top of the great cavity. The density of 
the blast and the form of the discharging pipe are ordered 
so that the chief focus of heat is about the bottom of the 
boshes ; hence the ore has to descend about 38 feet per- 
pendicular, before it arrives at the place where the fusion 
is effected. This does not happen in less than 48 hours, 
so that the ore is all this time in a state of cementation at 
a high temperature in contact with the burning fuel, and 
in consequence is almost saturated with carbon when it 
reaches the hottest part of the furnace. Being arrived at 
this place, the limestone Hux, and the earthy particles of 
the coaks and ore run down into a slag, the iron is also 
pelted and more or less decarbonized, and in part oxyda* 
