ash-pan slide and hopper bottoms are closed before leaving enginehouse.

26. Q. What is a "wagon-top" boiler?

A. It is a boiler that has the fire-box end made larger than the
cylindrical part to provide more steam space.

27. Q. Why are boilers provided with steam domes?

A. To furnish more steam space and to obtain dryer steam and to provide
a place for the safety valves, steam pipes, throttle valve and whistle.

28. Q. What must be the condition of a boiler to give the best results?

A. It must have good circulation and be clean and free from mud or
scale.

29. Q. What is meant by "circulation" in a boiler?

A. Free movement of the water, so that it may come in contact with the
heating surface and after being converted into steam be immediately
replaced by a fresh supply of water.

30. Q. What would be the effect if a "leg" of the fire-box became filled
with mud?

A. There would be no water in contact with the fire-box sheets and they
would quickly become overheated and mud-burned.

31. Q. What would be the result if the fire-box sheets became