SHEET ELUE SUPERHEATERS.

that the sectional elevation shows the super-heating tubes vertically arranged in the smokebox; and on alluding to the front elevation,the extension of this compartment will be seen.It will be noticed also that at the top left-handcorner of the boiler front a stop valve box issecured, having a vertical branch; this latterportion is connected to the supply pipe, whichpasses over the superheater to the roof of theboiler. At the bottom corner of the sectionalportion of the superheater, another stop valvebox is secured—but not shown—to permit thedischarge of the steam from the superheater.It is obvious from this description that thesteam enters the superheater at the top at oneend, and discharges at the bottom at the other,and thus a regular distribution of the steam iseffected. Perhaps the better position for thesupply valve is at the side of the boiler, orcentrally of the end of the superheater. Theposition of the valves and pipes, as represented,renders certain access for manipulation withinthe boundary of the stoking room, in front ofthe boiler ; a matter of the utmost importancewith vessels intended for war purposes. Thestop valve in connection with that supplyingthe superheater permits an independent flowof the steam to the engines, in which case thevalves previously alluded to are closed.

The passage for the volume from the smokebox is of course enlarged at the uptake end,and directly above the termination of the tubu-lar compartment a door or damper is hung, alsoone at the uptake. These dampers regulate themeans of exit, whether through the super-heater or the uptake. On closing the damperat the uptake and opening the one above, theheated products pass through the tubes of the

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superheater; and on reversing the position ofthe dampers, the apparatus in question is ren-dered non-effective.

The access for internal cleansing is notdeemed requisite in this instance, but theaccumulation from the smoke, &c., is readilyremoved both from the bottom plate and theinternal surfaces of the tubes.

SHEET FLUES.

The adoption of surface and time combinedwith superheaters must be correct in principleand efficient in practice, A certainty of thisis rendered more obvious when it is remem-bered that with the use of either functionseparately, the same result can be obtained.From the number of examples already noticed,it is apparent that superheaters have had theirshare of thought bestowed on them, and thateach authority has contended with his brotherin honest rivalry. It will be difficult, perhaps,to point out a more striking example, contrast-ing with those of prior notice, than thatillustrated by Fig. 36 on page 174.

The sectional elevation presents a similarityto that of a series of elongated boxes verticallysecured in the uptake. On referring, however,to the plan, it will be seen that the apparatusactually consists of an almost zigzag formedflue, through which the steam passes, as indicatedby the arrows. Now to render this peculiararrangement not only to be understood butto be appreciated, the following description isrequisite. The largest circle in the plan denotesthe funnel and the square form the casingencompassing the superheater, and those por-tions are also shown in the sectional elevation.The four stop valve boxes—one at each corner