COKE MANUFACTURE. 561 
larger pieces being placed near the center, and a mound of this kind, 
30 feet in diameter, and 5 feet high, will contain about 20 tons of coal. 
The exterior of the pile is covered with a bed of fine coke or breeze 
3 or 4 inches in thickness, which is packed down tightly to exclude the 
air, excepting a height of about 1 foot around the base, which is left 
uncovered. The pile is lighted by dropping some burning coals down 
the chimney, through the openings of which the coal is lighted, begin- 
ning at the base, and being propagated in all directions toward the 
cover. At the base of the pile where there is no cover, a small amount 
of air is admitted by which the combustion is sustained in the pile. A 
thick smoke soon rises from the exterior, and the flame, which is often 
very brilliant, escapes from the chimney. Im 4 or 6 days the fire will 
reach the cover, which then becomes red-hot, and the carbonization is 
then complete. The chimney is now closed by an iron plate, and the 
base of the pile, which has been left uncovered, is tightly sealed by 
moistened coke dust, as well as any other portion of the cover that may 
be broken. The management of the pile requires no little skill, espe- 
cially if the weather be bad or the wind blows, to prevent an unequal 
burning of the mound and a waste of the coal. At the end of 2 or 3 
days the pile will have become cool enough to permit the removal of 
the coke, which may then be quenched with water and drawn. The 
yield of coke from the Staffordshire coals, which are dry, is between 50 
and 60 per cent.; and while the product is not uniforn, only the large 
pieces of coal can be employed in the construction of the pile. 
The circular piles are sometimes made without any covering, and 
being lighted at the centre, where the fire reaches any portion of the 
exterior, as is shown by a coating of ashes, it is quenched by a covering 
of coke dust, and when the whole pile is so covered it is left to cool. 
The piles are also made with channels at the base, which radiate from 
the central chimney to the circumference. They are made of the larger 
pieces of coal, and permit a regular admission of air to the pile, which 
otherwise is tightly covered by fine coal or coke dust. 
Rectangulur piles or pits are used to some extent in England, and 
though formerly employed in many of the iron works of the United 
States, as at Johnstown, Hollidaysburgh, etc., they have in most instances 
given place to the use of ovens. 
There is a form of rectangular pile used at the Bowery Furnace, 
36 G. 
