f any of the valves stick they will sometimes be induced to
act again by working with the pet cock open, or alternately open and shut.
Should the defect arise from a leakage of steam into the pump, which
prevents the pump from drawing, the pet cock remedies the evil by
permitting the steam to escape.

750. _Q._--What precautions should be taken against priming in locomotives?

_A._--Should priming occur from the water in the boiler being dirty, a
portion of it may be blown out; and should there be much boiling down
through the glass gauge tube, the stop cock may be partially closed. The
water should be wholly blown out of locomotive boilers three times a week,
and at those times two mud-hole doors at opposite corners of the boiler
should be opened, and the boiler be washed internally by means of a hose.
If the boiler be habitually fed with dirty water, the priming will be a
constant source of trouble.

751. _Q._--What measures should the locomotive engineer take, to check the
velocity of the train, on approaching a station where he has to stop?

_A._--On approaching a station the regulator should be gradually closed,
and it should be completely shut about half a mile from the station if the
train be a very heavy one: the train may then be brought to rest by means
of the breaks. Too much reliance, however, must not be put upon the breaks,
as they sometimes give way, and in frosty weather are nearly inoperative.
In cases of urgency the steam may be thrown upon the reverse side of the
piston, but it is desirable to obviate this necessity as far as possible.
At terminal stations the steam should be shut off earlier than at roadside
stations, as a collision will take place at terminal stations if the train
overshoots the place where it ought to stop. There should always be a good
supply of water when the engine stops, but the fire may be suffered
gradually to burn low toward the conclusion of the journey.

752. _Q._--What is the duty of an engine man on arriving at the end of his
journey?

_A._--So soon as the engine stops it should be wiped down, and be then
carefully examined: the brasses should be tried, to see whether they are
slack or have been heating; and, by the application of a gauge, it should
be ascertained occasionally whether the wheels are square on their axles,
and whether the axles have end play, which should be prevented. The
stuffing boxes must be tightened, and the valve gear examined, and the
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