Now upcast eyes to heav'n adore, And knees that never bow'd before.
When it surmounts a single pit, or a single division of the pit, the compartment intended for the upcast is made air-tight at top, by placing strong buntons or beams across it, at any suitable distance from the mouth.
At other times, a circulation of air is produced by placing coal-fires in iron grates, either at the bottom of an upcast pit, or suspended by a chain a few fathoms down.
It then passes through the furnace with all the inflammable gas it has collected, ascends the upcast shaft, and is dispersed into the atmosphere.
Here the circulation is made active by rarefying the air at the upcast shaft, by means of a very large furnace placed either at the bottom or top of the shaft.
The same mechanism is mounted at the upcast shaft a, only here the funnel is made to present its mouth in the wind's eye.
A, coursed through the clean workings, up the dumb furnace D, till it reached a certain elevation in B, the upcast pit, above the fireplace.
Thus also a partial stagnation in one district of the colliery, would be produced by any of the common stoppings being accidentally removed or destroyed, since the air would thereby always pursue the nearest route to the upcast pit.
This is effectually done by two shafts, called respectively the downcast and the upcast shaft.
Where the upcast pit is used for drawing coal, it is usual to discharge the smoke and gases through a short lateral drift near the surface into a tall chimney, so as to keep the pit-top as clear as possible for working.
The usual form of ventilating furnace is a plain fire grate placed under an arch, and communicating with the upcastshaft by an inclined drift.
I should require to know the temperature of the shafts respectively, and the height of the upcast shaft.
I see one of the cages is at bank, and the force of the explosion is in the upcast shaft.
