STEAM BOILER 329 See King, "Lessons and Practical Notes on Steam," &c. (New York, 1860 ; 19th ed., 1873) ; Fairbairn, "Useful Information for Engineers" (3 series, London, 1864 '6); Salter, "Economy in the Use of Steam " (London, 1874) ; Perry, "An Elementary Treatise on Steam" (Lon- don, 1874) ; Relation des experiences de M. V. Eegnault (Paris) ; and Porter, " Steam Engine Indicator," containing a valuable steam table (New York, 1875). STEAM BOILER. The use of steam boilers dates from antiquity. Hero, who lived in the Jd century before the Christian era, described jveral forms of boilers which were used in Derating steam for what seem to have been variety of philosophical toys, one of which generally referred to as the earliest known iple of the steam engine. When steam _ in to be usefully applied, and considera- le pressures became necessary, the forms iven to boilers were approximately spherical, lipsoidal, or cylindrical. Thus the boilers of )e Caus (1615) and of the marquis of Wor- ster (1663) were spherical ; those of Savery [1698) were ellipsoidal and cylindrical. After 16 invention of the steam engine of Newco- len, the pressures adopted were again very >w, and steam boilers received irregular forms itil, at the beginning of the present century, ley were again of necessity given stronger lapes. The material was at first frequently >pper; it is now usually wrought iron, and letimes steel. The present forms of steam )ilers may be classified as plain, flue, and ibular boilers. The plain cylindrical or com- lon cylinder boiler is the only representative of the first class in common use. It is per- fectly cylindrical, with heads either flat or " 3mispherical. There is usually attached to boiler a "steam drum" (a smaller cylindri- il vessel), from which the steam is taken by le steam pipe. This enlargement of the steam 36 permits the mist, held in suspension by steam when it first rises from the surface of the water, to separate more or less com- pletely before the steam is taken from the boiler. Flue boilers are frequently cylindri- cal, and contain one or more cylindrical flues which pass through from end to end, beneath the water line, conducting the furnace gases, and affording a greater area of heating sur- face than can be obtained in the plain boil- er. ^ A cylindrical boiler, having one flue trav- ersing it longitudinally, is called a Cornish boiler, as it is generally supposed to have been first used in Cornwall. It was proba- bly first invented by Oliver Evans in the Uni- ted States, previous to 1786, at which time he had it in use. The flue has usually a diam- eter 0-5 or 0-6 the diameter of the boiler. A boiler containing two longitudinal flues is called the Lancashire boiler. This form was also introduced by Oliver Evans. The flues have one third the diameter of the boiler. Sev- eral flues of smaller diameter are often used, and when a still greater proportional area of heating surface is required, tubes of from 1 in. to 4 or 5 in. in diameter are substituted for flues. The flues are usually constructed by riveting sheets together as in making the shell or outer portion. They are sometimes welded by British manufacturers, but rarely if ever in the United States. Tubes are always "lap- welded " in the process of rolling them. Small tubes were first used in the United States, about 1785. In portable, locomotive, and ma- rine steam boilers, the fire must be built with- in the boiler itself, instead of (as in the above described stationary boilers) in a furnace of brickwork exterior to the boiler. The flame and gases from the furnace or fire box in these kinds of boiler are never led through brick pas- sages en route to the chimney, as often in the preceding case, but are invariably conducted through flues or tubes, or both, to the smoke stack. These boilers are also sometimes used as stationary boilers. Fig. 1 represents a steam fire engine boiler in section, as usually exhibit- ed in working drawings. F is the furnace, W the water space, and S the steam space. This is the form of boil- er adopted for the steam fire engine described in the ar- ticle FIRE ENGINE. In these boilers the fire is usually urged by the blast pro- duced by the ex- haust from the en- gine cylinder, and is thus rendered very intense. The tubes are frequently made of brass or of cop- per, to secure rap- id transmission of heat to the water, and thus to permit the use of a small- er area of heat- ing surface and a smaller boiler. The steam space is made as large as possi- ble, to secure immunity from "priming" or the " entrainment " of water with the steam. This type of steam boiler was the earliest of the tubular boilers. It was invented by Na- than Read of Salem, Mass., in 1791, and pat- ented in April of that year. In the locomo- tive boiler, fig. 2, as in the preceding, the characteristics are a fire box at one end of the shell and a set of tubes through which the gases pass directly to the smoke stack. Strength, compactness, great steaming capaci- ty, fair economy, moderate cost, and conve- nience of combination with the running parts are secured by the adoption of this form. It is frequently used also for portable and sta- tionary engines. It was invented in France by M. Seguin, and in England by Booth, and FIG. 1. Steam Fire Engine Boiler.
