A. When the hot air of the chimney has been cooled by the external air, it can no longer buoy up the solid smoke; so it falls to the earth in condensed flakes, called “blacks.”
Q. Why are there no blacks in the smoke of a railway engine?
A. The smoke of a railway engine consists chiefly of watery vapour, which dissolves in air, as sugar does in water; but the smoke of a common chimney consists of small fragments of unburnt fuel.
Q. Why does a “COPPER HOLE” DRAW up more fiercely than an open stove?
A. As the air, which supplies the copper hole, must pass through the furnace, it becomes exceedingly heated, and rushes up the chimney with great violence.
Q. What produces the roaring noise made by a copper-hole fire?
A. Air rushing rapidly through the crevices of the iron door, and up the chimney flue.
Q. Why is the roar less, if the copper-hole door be thrown open?
A. Because fresh air gets access to the fire more easily; and as the air is not so intensely heated, its motion is not so violent.