Boiler
the name given to a vessel in which steam is generated. In its simplest form, it consists of a close vessel made of metal plate, having apertures for the admission of water and egress of steam, fitted with apparatus for showing the level of the water and the pressure of the steam, and in connection with a furnace. When water is boiled in an open pan, the temperature of the water and of the steam rising from it remains at 212° F., and the tension or pressure of the steam is no more than sufficient to make its way into the atmosphere, being exactly equal to that exerted in all directions by the atmosphere itself-14.7 pounds per square inch. In a close vessel, on the other hand, the temperature and pressure to which we can raise the steam are only limited by the strength of the boiler.
The form of a boiler is determined by two considerations-namely, strength to withstand internal pressure, and efficiency in producing steam. The globular form is that best adapted for strength, furunculus. It is a phlegmonous tumor, and was the earliest to be used. It prewhich rises externally, attended with redness and pain, and sometimes with a violent, burning heat. Ultimately it besents to the fire, however, the minimum area in proportion to its contents, and, comes pointed, breaks, and emits pus. A therefore, has a minimum efficiency. Afblind boil is one which does not suppurate.