MANUFACTURE OF BOILERS.

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plate, and all the outside edges should be placed downwards; thusthe moisture freely runs down, and is not allowed to collect at theseparts, preventing the rapid corrosion that would otherwise set in.The drawing should plainly show all the laps, to prevent the work-men from plating the boiler incorrectly. The plates exposed to theimmediate action of the flame should be of the best description,more especially in the crowns of the furnaces, where they must runlengthways, and all the joints kept wellout of the fire. Sometimes the furnacesare plated with butt joints and strips;this is a good plan for boilers intendedto carry high-pressure steam. The end-plates of rounded boilers are usuallyattached and stayed to the shell withangle-iron at the corners, having threeor more flat plate-stays, rivetted be-tween two angle-irons at the endsand top, dividing the surface to bestayed equally. When the furnacesare inside of the boiler the angle-ironfor joining the furnace with the end-plate is placed inside, at the furnaceend, and outside of the flue-plates at theextreme end; but should the furnace be underneath the boiler theflues must be joined to the end-plates with angle-iron outside ofthe flues, or, in other words, inside of the shell. The water spaceunderneath the boiler in this case will be more than in the formerarrangement, with 2^ inches breadth of angle-iron, not less than5 inches between the flue J plates and the outside shell; and wheretwo furnaces or flues are adopted, the same space should be betweenthem: when stronger angle-iron is used the distance may be thesame, but the angle-iron will require to be flattened or cut awayat that point.

Sometimes boilers are ordered to be flanged in all the corner plates.When so specified, all the flanges should have a bold radius at thecorners, not less than 2 inches: this makes a neat piece of work, andthe strength of the boiler is materially increased. Water spaces,having flat sides, should be stayed together with ^ inch screwedstays, tapped into both plates, and rivetted or fitted with nuts andwashers outside, as occasion may require, the distance between

Fig. 43.—Plate-stays.

R, GHAPLtH