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never work so safely as a properly constructed internally-fired boiler,as they are so liable to fracture at the seams over the furnaces,through the excessive alternate expansion and contraction to whichthey are exposed. The application of stout longitudinal stays wouldadd materially to the safety of such boilers. A variety of cylindricalvertical boilers are used in various iron-works. These boilers aregenerally heated from the puddling or similar furnaces, the heatfirst entering the external flues, and passing thence by an internaldescending flue-tube to the chimney. They are especially liable tostarting and fracture of the rivetted seams opposite the furnacenecks, owing to the intense heat at that point; and where the feedwater deposits much sediment the solid plate is sometimes fractured.To avoid this liability the part referred to should be protected by ascreen of brickwork, or the boiler set at a higher level; the brick-work may be so arranged as to spread the heat before it reaches theboiler. The bottoms of these boilers are frequently quite inaccessiblefor examination, and serious corrosion may go on unknown to thosein charge. If the boilers were supported by brackets at the side, orby wrought-iron plate Standards rivetted to the bottom, so that athin wall of brickwork would suffice to form the flues, the conditionof the plates could be occasionally ascertained without much diffi-culty.
“As the safety of boilers depends so much on the sufflciency andcondition of their Attings, a few remarks thereon will be useful. Itis well to have two safety-valves to each boiler, as a check upon eachother; oneof them should be a dead-weight valve, loaded externally,and the other a lever-weight valve, or a compound valve, whichwould allow the steam to escape, if the water were allowed to fallbelow the proper level. Safety-valves are frequently met with, thelevers of which are of such length, that the usual working pressurefor which the boiler was made would be much exceeded if the weightwere fixed at the end of the lever. The weight should always becalculated and adjusted to hang at the end of the lever. All boilersshould be provided with correct pressure-gauges for the guidance ofthe attendants. The glass-gauge is undoubtedly the best and mostreliable water-gauge, and it is a good plan to attach two gauges toeach boiler. Where floats are used there should be two, one ofthem fitted with an alarm whistle. Boilers with internal tubes shouldalways be fitted with glass-gauges. Fusible plugs should be insertedin the furnace crowns of all internally-fired boilers. The feed regu-