gularly maintained, the fluctuations of
temperature cause constant contraction and expansion to take place. If
the fire is not carried level, but is carried heavy in some parts of the
fire-box and light in others, holes will be worked in, cold air drawn
through, lowering the temperature, chilling the tubes and causing leaks.
Carrying the fire too heavy in some places, causes clinkers to form. If
the door is open too long, too much cold air is drawn over the fire,
causing the tubes to leak.

51. Q. What do you consider abuse of a boiler?

A. Careless or improperly supplying water to the boiler, improper firing
or allowing steam to vary from high to low pressure, causing unnecessary
expansion and contraction.

52. Q. Does the stopping up of flues affect the steaming capacity of the
engine?

A. Yes; obstructed flues reduce the heating surface, reduce the steaming
capacity of the engine, and, as a rule, result in causing the flues to
leak. They also cause an increase of speed of the gases through the
remaining flues and a poor steaming engine.

53. Q. What causes honeycomb over the flues?

A. Honeycomb on flues is usually caused by the draft through the fire
picking up the sulphur and molten clay which is in a molten and sticky
condition in the fire; as it passes on its way to the stack, some of it
strikes the flue-sheet and sticks or passes through the flues, clogging
up the netting in the front end.

54. Q. How would you take care of a boiler with leaky tubes or fire-box,
and why?

A. Keep a bright, clean fire, especially up next to the flue-sheet, and
as even a pressure of steam as possible and not use the blower any
stronger than is absolutely necessary.

55. Q. Why is it very important that coal should be broken so that it
will not be larger than an ordinary sized apple before being put into
the fire-box?

A. In order to get rapid and complete combustion, coal should be broken
into small pieces; this aids combustion by exposing a larger surface to
the flame and can be fired more economically and better results are
obtained.

56. Q. Should rapid firing be practiced?

A. No; it should not be practiced for the same reason that heavy firing
is wrong. A few moments should intervene between each shovelful to allow
the fresh coal to get to burning and to maintain the high temperature in
the fire-box.

57. Q. When and why should you wet the coal on the tender?

A. Coal should be wet for the purpose of cleanl