Fig. 30.
Fig. 31.
The same remark applies to some of the portable or agricultural boilers which have exploded, such as those shown in [Fig. 30] and [Fig. 31], [No. 43, 1868], and [No. 12, 1869].
Fig. 37.
Much mischief is often caused by bad imitation of well planned boilers. Thus in boilers of the Cornish form, the ends are made sometimes so rigid as to give no allowance for the expansion of the tube, and the result is such continued strain as to cause constant leaking and the consequent risk of fracture. In furnace boilers the tops of the crowns of the inside tubes are often made flat, as in [Fig. 37], instead of being domed; or the inside tube is of undue size, as in [Fig. 21], [No. 23, 1870], see page 73. Furnace boilers have been made with the omission of the stays that are so peculiarly necessary in that form, whereby both ends have been left free to bulge outwards with the pressure, as in [Fig. 32].
