on. Black smoke is
not combustible, it is like lampblack and cannot be burned after having
been produced. The production of it can be prevented by suitable
arrangements and manipulation.

32. Q. Should the gas not burn in the fire-box, will it burn after it
enters the flues? Why?

A. Gas will not burn only a short distance in the flues of a boiler, as
the water absorbs the heat so quickly that the temperature of gas is
lowered below the igniting point.

33. Q. What is the effect on the flow of air through the fire from
opening the door? What on the burning of the gases? What on the flues
and sheets of the fire-box?

A. When the furnace door is opened, the flow of air through the grate is
stopped in proportion to the amount that passes through the door. The
vacuum will be filled from the quickest source and the door is closer
than some parts of the grate. The gases mix with the air from the door
and pass out through the flues; no combustion takes place, as the air
is not hot enough to unite with the gas. The flues and sheets of the box
will be caused to leak on account of the rapid contraction.

34. Q. Can the firing be done more effectively if the water level is
observed closely?

A. Yes, in order to know how much water there is in the boiler and
whether it is necessary to hurry the fire; if the boiler is full, it is
possible to prevent the pops opening by delaying the fire.

35. Q. How should the fire and water be handled in starting from a
terminal or other station?

A. The steam pressure should be near the maximum and there should be
sufficient water in the boiler to last until such time as the fire is
burning well so that the pressure will not be reduced when water is put
into the boiler. There should be a moderately heavy bed of fire well
burned and distributed evenly over the grates. After the fire is burning
well, the injector should be started lightly; the feed being gradually
increased so as not to cause any decrease of steam pressure.

36. Q. What is the purpose of a safety valve on a locomotive boiler? Why
are more than one used?

A. A safety valve is used to limit the maximum pressure in the boiler by
opening and allowing steam to escape. More than one safety valve are
used as additional protection against excessive pressure; one is set at
the maximum pressure and the others are set at two or three pounds above
the maximum pressure.

37. Q. What is usually the reason for steam being wasted from