drivers to slip with the fire too thin on the grates?

A. The fire would be pulled off the grates and into the tubes, leaving
the fire bed full of holes and some of the fire remaining on the grates
turned over. Large quantities of cold air would be drawn in, resulting
in a rapid decrease of temperature and pressure. The tubes would
possibly start leaking and the fire would be in such condition that it
could not be built up properly in a long distance. Possibly the grates
would become clogged up with green coal--an excellent opportunity for
forming clinkers. In this condition, the engine 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?