67. Q. Then why not heat the feed water to the boiling point (212
degrees)?

A. If the feed water is heated much above 100 degrees it will not
condense enough steam in the injector to cause it to work properly. Some
injectors will work hotter water than others. It would also spoil the
paint on the tank if heated to a much higher temperature.

68. Q. At 200 pounds pressure per square inch, what is the pressure per
square foot on the sheets of a boiler?

A. About fifteen tons.

69. Q. What is the total pressure on the fire-box of a large
locomotive?

A. Over 3,000 tons.

70. Q. Give a practical definition of heating surface.

A. The heating surface of a boiler includes all parts of the boiler and
tubes that are directly exposed to fire or heat from the fire and are
surrounded by water.

71. Q. Should an engine be slipped to get water out of the cylinders or
steam passages?

A. No; the water should be worked out by opening the cylinder cocks and
starting the engine slowly.