Brick, brick arch supported upon water-tubes, which extend diagonally from below the tubes to a point nearly midway of the length of the crown-sheet, has been tried; also one carried by tubes extending diagonally from below the tubes to a line in the back of the fire-box just above the fire-door. The brick arch was first employed in 1854 upon the Pennsylvania Railroad. Figures 5 and 6 (N. 75) show one variety. The long combustion-chamber with a water-bridge was produced for the New Jersey Railroad and Transportation Company about 1861. In the follow ing year the.! Chicago, Burlington, mid (uiney Railroad tried a water-leg which projected diagonally upward from the front of the fire-box in face of the door; and about four years later this was followed by the much discussed brick arch, having- the same position and inclination. The diagonally-inclined water-leg was developed into the Buchanan water-leg (figs. 2), which extended diagonally upward entirely across the fire-box, leaving only a hole for the passage of the gases of combustion.
the substitution of coal for wood as fuel, iron tubes were used in the United States instead of copper and brass, and leaky tubes were at first common by reason of there being no steam-gauges in general use, the safety-valves the only guides as to the pressure. Tubes were at first fastened by expanding them in by a tapered mandrel driven in, and then a wrought-iron thimble was driven in. The introduction of cast-iron thimbles instead of brass is due to Hudson, and they were first used upon the Erie Railway. Copper tube-ends brazed on, with a steel thimble, were found to give tight tubes, but a better way was soon adopted by putting the copper end outside the iron tube and by using the end of the tube itself as the thimble. In 1835, Baldwin patented the method of driving a copper ferule on the outside of the end of the tubes, instead of inside.
Engines. —Builders on the American side of the Atlantic early became convinced that inside-connected engines—that is, those having cranked axles—cost more to build and to keep in repair than those with outside cylinders, and required more skill in counterbal ancing, while they were no steadier nor faster. The " Stockbridge " of 1842 OM cy, fig. 5) had outside cylinders, but a pair of trailing wheels be hind the driving-axle considerably reduced the adhesion. In 1836, Camp bell patented the use of two pairs of drivers connected by a side rod or parallel rod (fig. 2), and in 1844 this was adopted by Rogers and became known as the "American" type. The first Rogers's engine which had
this arrangement is also claimed to have been the first to have an equal izing beam between the driving-wheel and the truck (fig. 6). Outside cylinders were first bolted to the smoke-box, which method was feasible because the cylinders were inclined downward. But with horizontal cyl inders it was necessary to extend the smoke-box downward and to give it a base, generally of rectangular outline with a reinforcing piece around its front edges inside. Inside cylinders were fastened to the smoke-box and frames by means of two castings, which fitted the lower cylindrical side of the smoke-box and were bolted together in the middle. Later the smoke-box was given a rectangular downward projection, with a cast-iron bottom and a distance piece, and the cylinders were bolted to the sides of this projection and to the flames. This developed into a design which added a cast-iron bottom to the smoke-box. Next, the box was kept cyl indrical and a heavy bed casting was bolted to its lower side, with pas sages cored in it for the steam- and exhaust-pipes, the cylinders being bolted to its sides. This was followed by the plan, now in general use (p. mo, fig. 6), of making the saddles in halves bolted to the bottom of the cylindrical smoke-box, on the top and together in the centre, each casting being made in one piece, with the cylinder on that side. By 1S65 hori zontal cylinders were the rule. A good illustration of the cylinders of American locomotives is shown in Figure 7. These cylinders are revers ible and interchangeable, and are made of the best close-grained iron as hard as can be worked.
locomotive frames were of plates, with wood-filling between, and the journal-bearings were outside the wheels. Bury intro duced the bar-frame, which is now exclusively used in the United States, and is one of the distinguishing characteristics of the American engine. At first the whole frame was forged in one piece, but afterward for conve nience in repairing the front and back ends were made separate and then bolted together. Some narrow-gauge engines have the main frames in the usual position inside the wheels, but have a supplementary frame or offset bolted to this to carry the fire-box. The old style of wooden frames was abandoned by Baldwin in 1839, and no outside frame whatever em ployed, the machinery as well as the truck and the pedestals of the driv ing-axles being attached directly to the naked boiler.