The allowance for the rivets being in double shear is 75 per cent., or in other words, a rivet in double shear is allowed 1.75 times the area of the same size rivet in single shear.
STATIONARY ENGINE BOILERS.
The simplest form of horizontal boiler is the plain cylinder boiler, an example of which is given in [Fig. 3259], and which is largely used in iron works and coal mines.
![[Largeimage(106 kB).]](#8656825660018214284_large0915b.png.id-1988818446626107825.wrap-0.html.html){kind=link}
Fig. 3259.
Boilers of this class are easily cleaned, because the whole interior can be readily got at to clean.
As the bottom of this boiler gets thinned from wear, the boiler is turned upside down, thus prolonging its life.
