COKE MANUFACTURE. 569 
the volatile matter, which burns in the vault of the oven above the bed 
of coal, and nota little’skill is required, especially in stormy weather, 
to so regulate the admission of air that there shall be no excessive burn- 
ing of the coal. As long as the distillation continues, and volatile 
matter is being expelled from the coal, it will be denoted by the 
flame at the top of the oven. When the flame ceases, the volatile 
matter has been driven off, and the coking operation proper com- 
pleted. The front door is now luted up tightly to exclude all air, 
and an air-plate is placed over the opening in the top, which is covered 
with ashes to seal it tightly. The oven is then hermetically sealed, 
and is left to cool for 12 hours, at the expiration of which time the 
brickwork is removed from the doorway, and the coke quenched by water 
introduced through a long iron pipe. This quenching of the coke requires 
a few minutes only, when it is ready to be withdrawn. A small iron 
bar is placed across the doorway, and held in place by staple on either 
side, and upon this the workman rests the handle of the long rake or 
hoe with which he hauls the coke from the oven. ‘This is an exceed- 
ingly arduous labor, and requires about 20 minutes for the complete 
cleaning of the oven. If the coke should not be thoroughly extin- 
guished it is wetted again with water, and then shoveled into wagons 
by pronged forks, that leave the fine and useless coke dust. The oven 
having been cleaned, a new charge is then made, as already described. 
The total time of the operation at Riddlesburgh is usually 36 hours, 
though it is sometimes prolonged to 72 or 76 hours. This increased 
time is principally added to the time of cooling, and though the coke is 
made more dense and hard, the advantage is not always repaid by the 
increased expense. 
The coal employed at Riddleburgh is the Broad Top semi-bitumi- 
nous coal, similar ‘to the Cumberland. The coal is now washed before 
coking. The yield of the coal by weight is from 58 to 60 per cent. of 
coke. | 
In the region producing the celebrated Connellsville coke, in the 
vicinity of Connellsville, Pa., the same form of oven is exclusively 
used, about 113 to 12 feet in diameter and 6 feet in height. The coal 
employed is from the Pittsburgh seam, which here has been somewhat 
metamorphosed, so that it is in fact a semi-bituminous coal.. The com- 
position has been already quoted on page 559. It is quite friable in 
character and readily breaks up into pieces of a small size, leaving little 
