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