The 'cow-catcher.' or pilot. placed in front to remove obstacles from the track, the bell, and the whistle were also American developments. The severity of the winter storms compelled the adop tion of the 'cab.' and the use of wood for fuel led to the invention of the spark-arrester for wood burning engines. The heavy grades of American roads led to the development of the sand-box as a requisite appliance.
CoNsTauctiox. Structurally a locomotive con sists of a frame, the boiler and engine supported by it, and the running gear on which the whole travels along the track. Since the boiler at present sets the limit of power that a locomotive is capable of exerting, a description of modern locomotive construction may properly begin with this important part.
The boilers used upon locomotives are of a dis tinct type. They consist of an approximately cylindrical barrel or shell filled with longitu dinal tubes and having an internal fire-box or furnace at one end and an attached smoke-box and stack at the opposite end. Fig. 7 is a longitudinal section of such a boiler with the attached parts indicated. The tire-box is sur rounded on all sides except the bottom by the boiler water, and to support and Maintain in place its top and four sides they have to be at tached to the adjacent sheets of the boiler shell by stay-bolts. 8tuy-bolls are of various forms. An ordinary form is a round steel rod threaded at its ends, one end being screwed into a hole in the fire-box sheet and the other end into a hole in the adjacent sheet, and the two ends then riveted over or headed. Usually a small hole is drilled into the fire-box end of each stay-bolt, which series as a ;warning, if the bolt becomes broken, by allowing a small stream of water to escape into the fire-box. The form of stay bolt just described is known as a rigid stay-bolt. Flexible stay-bolts are also employed; these are binged at one end, usually by means of a hall and socket joint, so that unequal expansion of the two sheets connected is possible without bending the stay. To support the top or crown sheet of the fire-box, two means are employed; one is to use long radial stays from the crown sheet to the boiler shell, and the other is to suspend from the shell by means of sling stays a number of crown bars which are stay-bolted to the crown sheet. Various combinations of these methods of support and of the several forms of stay-bolts are also employed. The staying of the crown and side and end sheets of locomotive fireboxes is one of the most difficult and important details of locomotive boiler construction. The enormous warping effect of the fire-box sheet due to the fierce fire on one side and the water on the other side would soon destroy the.sheets were they not
securely bolted in position. The stays are con sequently put in very close together and only the best material and workmanship is countenanced. Even when all these precautions are taken nmeh trouble results from broken and leaky stay-bolts and from warped sheets.
Tho boiler shell is nearly always made of sheet steel; the tubes are sometimes made of steel, but are more often of wrought iron. Wrought iron is the preferred material for stay-bolts also. In outer form locomotive boilers are either straight-top boilers or wagon-top boilers. The straight-top boiler is one whose shell is a recti linear surface from front to rear; a wagon-top boiler (Fig. 7) is one whose shell is cylindrical for part, of its length from the front end and then bulges up and outward to a considerably larger diameter at the rear end. Some forms of boiler have received special names. The Bel peire boiler is one in which the crown sheet and sidg sheets are rectilinear planes instead of tainted surfaces. The Lentz, boiler has a cylin drical corrugated tire-box and requires no stay bolts. A Thoottca boiler has a wide shallow fire box with the grates above the tops of the driving wheels; it is designed for burning anthracite, which more grate area than does bi tuminous coal.
Generally speaking, the locomotive fire-box is rectangular in plan and is roughly of balloon shape in vertical transverse section. The top sheet is called the crown sheet, those at the two sides are called side sheets, those at the two ends are called the front and rear tube sheets. For merly it was the practice to make the fire-box narrow, so that it would sit between the engine frames, but the more common practice now is to set iL on top of the frames and thus obtain greater width and length. The bottom of the tire-box is formed by a grate. ("rates are of various forms. For burning wood a stationary grate, consisting of a heavy east-iron plate per forated by narrow slats arranged in rows, is used. For burning bituminous coal movable or rocking grates are invariably employed. For anthracite coal similar rocking grates are used, and use is also made of water-grates. In water-grates the grate-liars are hollow tubes connecting with the front and rear water-legs of the fire-box and are consequently kept filled with water. Generally all the grate-bars are not water-tubes, hut a few of these are alternated with solid bars which can be moved to shake and dump the fire. Many engines are now constructed for burning oil fuel, and the fire-boxes are adapted to its use with but few changes.