BOILER. In steam engineering, a vessel in which steam is generated at a high pressure for heating or power purposes.. In its simplest form, it consists of a closed vessel made of sheet metal, having apertures for the admission of water and egress of steam, fitted with appara tus for showing the level of the water and the pressure of the steam, and set or mounted in combination with a furnace, either internal or external. When water is boiled in an open pan, the temperature of the water and of the steam rising from it remains at, or very near, 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 ex erted in all directions by the atmosphere itself— namely. 14.7 pounds per square inch. In a closed vessel, on the other hand, the tempera ture and pressure to which we can raise the steam are only limited by the strength of the imagination. Ile has been studied by generations because his is the art that can be learned, as Pope, his best pupil, learned it, though his own Horace might have taught him that the true poet could not be made. Boileau repeated and enforced his critical views in the prose Dialogue des heros de roman, whose authorship he at first concealed, and in llellexions critiques stir Longin (1693). His own best verses are twelve Epitres and a mock-heroic epic. Le lutrin, which was his most popular work. It was published in part in 1673, but not in full till after his death. This and all the poems are tilled with cleverly turned lines that remain as familiar quotations. but should he most gratefully remembered as the first systematic critic of France, the first to make criticism an art. Be was narrow and some times unjust, he never fully grasped the funda mental principles of the classic art he admired; but his honest, loyal, stubborn, rough good sense did much to direct the talent of \loliere, Racine, and La Fontaine to its most fruitful channels and to guide the next generation to a true, though partial, naturalism. On the lyric poetry of suc ceeding generations its effect was to cultivate a formal technique and so to check inspiration that first fully revives in the Romantic School.
vessel or boiler against bursting. The form of a
boiler is determined by two considerations— namely, strength to withstand internal pressure, and efficiency in producing steam: and the ob ject of the designer is to combine in one appara tus sufficient strength to work safely at the proposed pressure, with such a form and arrange ment as shall abstract the maximum of heat from the gases of combustion, and at the same time be in all respects suitable to the special circumstances of the case. The globular form is that best adapted for strength, and was the earliest to be used. It Presents to the fire, however. the minimum area in proportion to its contents. and therefore has a minimum etli cieney. After spherical boilers, cylindrical ones came into use, at first set on end. and after wards laid on their sides, and later on these were furnished with internal cylindrical tubes for furnaces. Watt's 'wagon boiler' (so called from its shape) was used for many years, butt being quite unfit for any but the lowest pres sures, it has long been discarded; and the 'egg end' boiler, or plain cylinder with hemispherical ends, also much used at one time, has now almost disappeared on account of its small evapo rative efficiency, it being used only where large quantities of waste fuel material, such as saw dust, can be had practically without cost.
Modern steam boilers may be classified ac cording to their form and construction. or ac to the character of their employment. Under thy first division we have horizontal and vertical boilers, internally and externally fired boilers, shell and sectional boilers, tire-tube and water-tube boilers. or boilers combining two or 1111 we of these several feattm-s. I'mler the second division are included stationary boilers, locomo tive boilers, marine boilers, and various forms of portable or semi-portable boilers. The variety of forms and of construction of station ary boilers are very great, but the bwoinoti ye boiler is practically limited to a single form, and marine boilers are nsually of the drum type known as the Scotch boiler, although water tube boilers of various forms are coining into use more and more. Recently considerably at tention has been devoted to the development of a holler for automobiles. See ArromounE.