A. When the opening of a chimney is large, the top must be contracted by a chimney-pot, in order to increase the draught.
Q. How does a chimney-pot increase the draught of a chimney?
A. As the same quantity of hot air has to escape through a much smaller opening, it must pass through more quickly.
Q. Why do tin blowers help to get a fire up?
A. Because they compel the air to go through the fire, and not over it; therefore the fire is well supplied with oxygen, and the draught greatly increased.
Q. Why does a tin blower increase the draught?
A. As all the air which enters the chimney has to pass through the fire, it is much hotter, and ascends the chimney very fast; and the faster the air flies up the chimney, the faster it rushes towards the fire also.
Q. Why does a parlour often smell disagreeably of soot in summer-time?
A. The air in the chimney (being colder than the air in the parlour) descends into the room, and leaves a disagreeable smell of soot behind.