50. Q. Has improper firing any tendency to cause the tubes to leak? How?

A. Yes; if the pressure is not regularly 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