COKE MANUFACTURE. 571 
80 horse-power boiler, with a chimney at either end, which are used 
alternately. The charging and discharging is made by the same doors, 
and as the gas first evolved from the coal has little combustible matter, 
having much water, it is let escape for 2 or 3 hours through the small 
side chimneys At the expiration of this time these are closed, and 
the central one is opened. This has an area. equal to the sum of 
the two others, and through it the gases are aspirated by the main 
chimney and burn around the boiler. When the boilers need repairing, 
the gases are let escape by the chimneys, and men may then enter 
the space around the boiler through arch-ways left for that purpose. 
One of these batteries of 8 furnaces is said to produce steam sufficient 
for the blowing engine of a large coke furnace, and by regulating the 
working of the ovens so that they are discharged at intervals of 3 hours, 
sufficient heat is always available for the boiler. The charge is 23 tons, 
and the time of the operation 24 hours. : 
The square, anchor, or as it is sometimes called, the Gibson furnace, 
has been used on the west coast of France for coking the English coals, 
and is known as the Boulogne-sur-mer oven, while it has been used to 
some extent in Germany and in England, where it originated. The 
oven is about 127 feet long, 63 wide and 6% feet in height at the back, 
flaring a little toward the front, so as to facilitate the discharging. 
The door is made the full width of the oven, and the coke is withdrawn 
at once in one piece by the anchor, which {is placed in the oven be- 
fore charging the coal. It is hence firmly imbedded in the coke at the 
end of the operation, and a chain being attached to it, it is drawn out 
with the coke by means of a capstan. Though it might be urged that 
the door is too large, causing difficulty in closing the oven tightly, and 
also that the anchor would rapidly be worn out, in practice, there is 
said to be no inconvenience from either of these. 
The furnace will contain 4 to 43 tons of coal, which is charged from 
the front, and the operation is conducted as in the round oven. The 
gases escape to the chimney by the flue shown in the figure. The time 
usually required for coking is about 48 hours, aud at Doulais furnaces 
containing 33, yield 73 per cent. of coke. 
In some furnaces erected on this plan in France, etc., small canals 
are built in the walls, so that at the termination of an operation air may 
be admitted to them, and the walls cooled down very much before dis- 
chargiag the coke. 
