the safety
valve? What can be done to prevent this waste?

A. Careless firing, careless running. Both engineer and fireman work in
harmony to obtain the best results.

38. Q. What is the estimated waste of coal for each minute the safety
valve is open?

A. About fifteen pounds. The estimated waste of steam when an engine
pops equals every second all the heat obtained from a quarter pound of
coal. Safety valves usually remain open about half a minute, resulting
in the loss of about eight pounds of coal.

39. Q. What should be the condition of the fire on arriving at a station
where a stop is to be made?

A. On approaching the station where a stop is to be made, firing should
be stopped far enough back to allow the carbon gases to be consumed
before the throttle is closed, so there will be little or no black smoke
from the stack and yet have sufficient fire that it will not be
necessary to feed the fire again if a short stop is to be made until the
train is started and the engine cut back or nearly to the running
cut-off.

40. Q. How should you build up the fire when at stations in order to
avoid black smoke?

A. Put in small quantities of coal at a time, have the door slightly
open and have the blower on lightly; good judgment must be exercised by
the fireman.

41. Q. Why is it that if there is a thin fire with a hole in it the
steam pressure will fall at once?

A. Because too much cold air is drawn into the fire-box and through the
tubes, retarding combustion and cooling the fire-box and tubes.

42. Q. If the injector is to be used after throttle is shut off, how
should the fire be maintained?

A. A sufficient quantity of coal should be placed on the grates to
maintain the maximum steam pressure and the blower used to keep the fire
burning brightly.

43. Q. What would be the result of starting a heavy train or allowing
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