FUSIBLE SAFETY PLUG
Fig. 80.
If the accident of low water occurs at a time where it is important to continue operations with the least possible delay, a pine plug may be driven in the opening left by the melting of the fusible metal. In any event it is but a short job to renew the fusible cap, it being only necessary to unscrew the nut and insert a new cap, the rest of the device remaining intact.
The plug should be renewed occasionally and the surface exposed inside the boiler be kept free from scale and deposit. It is to be understood that the fusible portion extends entirely through the shell of the boiler and when melted out makes a vent for the water or steam.
All marine boilers in service in the United States are required to have fusible plugs, one-half inch in diameter, made of pure tin, and nearly all first-class boiler makers put them in each boiler they build.
GRATE BARS.
Fig. 81.
The Grate Bars are a very important part of the furnace appliances. These consist of a number of cast iron bars supported on iron bearers placed at and across the front and back of the furnace. Innumerable forms of grate bars have been contrived to meet the cases of special kinds of fuel. The type in common use is represented in [Fig. 82.]
