THE MUD DRUM.
The mud drum is attached to a boiler with the expectation that it will catch and hold the larger portion of the sediment precipitated from the water. The mud drum to be effective should be protected from the heat of the fire, for so soon as it receives sufficient heat to boil the water within it can no longer serve the purpose for which it was intended as all the sediment which may have gathered would be expelled by the ebullition of the water. When the drum is located under the boiler it is not in a good position to catch the sediment, as the boiling water produces sufficient current to carry the sediment to the top, or keep it violently agitated, so that there is little opportunity for it to be deposited anywhere so long as the boiler is making steam. Afterward when the water is quiet the sediment for the most part is deposited on the tubes and the curve of the shell; the small portion falling into the neck of the drum serves principally to show the inefficiency of the device. Located under the boiler as it generally is, makes it extremely difficult to get at for examination, and as a consequence of its being enclosed, as it must be, to be of much importance, it is subject to greater deterioration than would otherwise be the case, and as the enclosure to be most efficient would enclose the neck also, the difference of expansion at or near the junction would soon produce leaking if not worse. When the mud drum is located outside the boiler walls where it would be most efficient, if properly connected, it loses its identity and becomes a mechanical boiler cleaner. In consequence of these drawbacks the mud drum is becoming antiquated as a boiler appliance, and is now seldom used.
BAFFLE PLATES.
These are a device sometimes used inside steam boilers to check the too sudden flow of steam towards the exit pipe, they are simply plate to baffle the rush of the steam so as to avoid foaming.
In [Fig. 90] baffle plate is illustrated by the division casting against which the steam strikes on its passage from the boiler to the engine. The liners or inner plates of the boiler doors are baffle plates.
DEAD PLATE.
This is a flat plate of iron immediately inside the furnace door and is used in many boilers in order to insure the more perfect combustion of the coal.
When the fresh fuel is laid on, it is placed on the dead plate instead of on the grate; in this position the coal is coked, the gases from the coal being ignited as they pass over the already intensely hot fuel in the furnace, the fuel from the dead plate is pushed forward to make place for another charge to be put on the dead plate. But more frequently, as elsewhere described, the fuel is thrown over and across the dead plate directly upon the hot fire.
STEAM WHISTLES.
These are of two kinds, known as the bell-whistle and organ-tube whistle; the latter is now fast superseding the former on account of the simplicity of construction and superior tone. An improved form has a division in the tube so as to emit two distinct notes, which may be in harmony, or discord, and when sounded together may be heard a long distance.