would fail to make steam
for the entire trip.

44. Q. Where should the coal, as a rule, be placed in the fire-box?

A. As a rule, more coal is burned along the sides and in the corners
than in the middle of the grates; the fire should consequently be kept
somewhat heavier along the sides and corners than in the middle.

45. Q. How is the fire affected by and what causes clinkers?

A. A clinker shuts off area of grate surface according to its size, and
thereby shutting off that much of the air supply and interfering with
proper combustion. Clinkers are caused by firing too heavy in spots,
which prevents sufficient air passing up through these spots and allows
the coal to run together, melting the ash, and sand; running a hoe or
slash bar through the fire will bring the points of melted sand
together, thereby causing a clinker.

46. Q. How can you best avoid their formation and dispose of them?

A. Light firing and occasionally moving the grates lightly is the best
preventive. When once formed, they should be removed if possible by
firing around and burning them out.

47. Q. How can you explain the slower burning of the coke and how
understand the proper manner of supplying fresh coal?

A. The gases of coal are lighter than air and will pass away whether
consumed or not. The slow burning of the coke is due to the fact that it
burns from the outside only. When a fire reaches a white or incandescent
heat it indicates that the gases are burned and a fresh supply of coal
should be added; this is to be done as light as the service performed by
the engine will permit.

48. Q. When and for what purpose is the use of a rake on the fire bed
allowable?

A. The rake should be used on the fire very seldom, because raking the
fire bed tends to form clinkers, especially when the rake is plunged
down through the fire to the grate. It may be used when necessary to
rake the fire lightly when on the road for the purpose of breaking the
crust, which may be found as a consequence of too heavy firing.

49. Q. Within what limits may steam pressure be allowed to vary, and
why?

A. Pressure should not be allowed to vary more than five pounds from the
maximum for the reason that too much expansion and contraction will
take place, which many times is the cause of flues leaking, cracked or
broken side sheets and stay bolts.

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

A. Yes; if the pressure is not re