ree months' hard steaming I blew
out the water and steam, took off the manhole cover, and there were the
things as I had left them thirteen weeks previously; of course they were
all coated with fine mud, but no signs of having moved a hair's breadth.

4. _Question._--But water in an open caldron with a fire under it, as in
the steam boiler, will madly sweep the sides and bottom with terrific
ebullition. How would you account for the great agitation in the open
caldron while the steam boiler had hardly any, although both vessels had
fierce fires under them?

_Answer._--In the matter of the open caldron the action of the water has
no resistance but that of the atmosphere, whereas in the steam boiler
the movement of the water is resisted from the moment it is heated, for
then a vapour rises above it, and, as the heat increases, the resistance
to the movement of the water is proportionally increased, and as the
heat of the steam increases the pressure on the water increases
proportionally all through, the steam being above the water. Any old
stoker knows that when getting steam up in a boiler the lower parts are
often only warm when there may be eight or ten lb. on the square inch in
the upper portions; when the water begins to boil the steam rises in the
form of minute globular particles, and remains above the water until
there is an outlet for it by opening the stop-valve or through the
safety-valve; and as the pressure is the same throughout every part,
nook and corner, and angle, there can be no dominating force to cause
any agitation within the boiler.

5. _Question._--What is superheated steam, and why is it used?

_Answer._--If a boiler is placed at a long distance from the engine or
whatever the steam may be used for, there is much or little condensation
according to the distance and the weather, so that there would always be
water mixing with the steam, and that is most objectionable where a
steam engine is concerned, and by super-heating the steam it comes to
the engine as hot and dry as if the boiler were close by; but whatever
the heat of the steam may be, the pressure cannot be increased after the
steam has left the boiler. In proportion to the pressure of steam so is
the heat of it; the higher the pressure the hotter the steam.

6. _Question._--If your water gauge-glass broke while the boiler was
working, how would you proceed to rectify the mishap?

_Answer._--By immediately shutting off both cocks