156 BRAITHWAITE'S NOVELTY" ENGINE. cally, one on each side of the boiler, and immediately over one pair of wheels; the other pair of wheels are connected with these by horizontal bars. The steam is generated in this engine on the same principle as in the "Rocket,” viz. by the draught of the chimney, aided by the escape into it of the steam from the cylinders. A horizontal section of the boiler, flues, and chimney, is shown in the following figure. The boiler is traversed D C B Fig. 66. by a tube which is bent upon itself like the letter; the furnace D, and the chimney C, are thus placed at the same extremity of the boiler; at this extremity, the tube projects from the boiler to an extent of about three feet, where it terminates in the chimney C. The upper part of the tube is surrounded at its two extremities by a semicircular case, for the purposes of obtaining an increase of heating surface and of draught. The hot air passes in the direction of the arrows B B from the grate to the chimney. 114. Braithwaite and Erickson's "Novelty" Engine.The third engine was the "Novelty" of Messrs. Braithwaite and Erickson. It differed from the preceding engines, in having no tender, the water tank and fuel being conveyed on the engine itself. The weight of this machine, with its load, was as follows: Some accidents occurred to the machinery of this engine during its journey, and it was consequently withdrawn, without having afforded sufficient trial to test its power. With BRAITHWAITE'S "NOVELTY" ENGINE. 157 the above load, it went at the rate of 17 miles per hour; with the load detached, it conveyed passengers at the rate of 28 miles per hour. This engine is of light and elegant appearance; its construction and modification are represented in the two following figures; the former represents the engine in profile; the latter is a vertical section of it; the letters correspond to the same parts in both figures. The principle by which the steam is here generated is different from that adopted in the preceding engines. A is the generator, or vessel in which the steam is raised; the lower part contains water, the upper part is filled with steam. Connected with this is a horizontal generator B, which being below the level of the water in A, is itself always full of water; the steam from B passes into A by the pipe H. The vertical generator A contains a tube C, fig. 68, which passes entirely from the top to the bottom; at its lower part it is enlarged, and receives the fire-grate F; the fuel is supplied from the top. The combustion of the fuel is effected by a strong blast of air produced by the bellows D, fig. 67, and conveyed to the fire-place through the tube E; the bellows 158 RESULTS OF THE FOREGOING EXPERIMENTS. are worked by the engine. The hot air from the fire traverses a tube e, which is twice bent within the horizontal generator, and then escapes into the air by the tube G. The steam cylinder K works one pair of the wheels by means of a bell crank;* the other pair are connected with B these by chains. Fig. 68. The action of this machinery will be readily understood by means of the vertical section, fig. 68. 115. Results of the foregoing Experiments.—The “Rocket” engine having undergone the whole trial, and fulfilled all the conditions laid down by the directors, the prize of £500 was awarded to Mr. Robert Stephenson, for this engine. Let us now consider the improvements which were effected by means of the competition at Liverpool; these relate, first, to the weight of the engine; and, secondly, to its increased evaporating power. 1. Previously to these experiments, an engine, weighing with its tender ten tons and The nature of the single crank has been frequently illustrated in the foregoing chapters; it can only be used upon the end of an axle. Fig. 69, represents the bell crank; it is obvious, from its construction, that it may be used upon any part of an axle; if placed between two wheels, it is capable of turning them both at once. Fig. 70, represents the double bell crank, which produces two alternate motions, reciprocating with each other. The ver Fig. 69. Fig. 70. tical bars attached to the cranks are the connecting-rods, which are worked by the piston. RESULTS OF THE FOREGOING EXPERIMENTS. 159 a half, was capable of drawing nineteen tons and a half, that is, a gross load of 30 tons, including the engine, at the rate of 10 miles an hour, on a level railway. But the "Rocket," weighing with its tender only seven tons and a half, drew nine tons and a half, that is, a gross load of 20 tons, including the engine, at the same speed. Such is the average estimate of the performances of the old and new engines. According to Mr. Scott Russell, the greatest loads drawn by the old locomotives were 284 tons weight, exclusive of engine and tender, at 10 miles an hour; while the "Rocket" drew 44 tons gross, exclusive also of engine and tender, at 14 miles an hour; or, in round numbers, the Rocket, only half the weight of the best drawing engines previously constructed, drew one-third more load at one-third more velocity. The result of this is important: the old engines had attained the maximum of weight practicable upon a rail; all further increase of power, therefore, resulting from increase of size was out of the question. In the new engine, a reduction of three tons weight was considered as so much additional weight capable of being added to the engine, and a proportionate increase of power was, consequently, expected. This anticipation has been amply verified. 2. An important result was also obtained in the economy of fuel. In the old engines, 18:34 lbs. of coke were required to evaporate a cubic foot of water; in the " Rocket," only 11.7 lbs. were required to produce a similar effect. But the advantage of an engine of light weight and small power is not to be estimated by the reduced consumption of fuel, for, by the "Rocket" itself, when travelling at a rapid pace, and drawing only three times its weight of carriages, the expense of fuel per ton per mile is greater than in the old engines. The real advantage of the new engine is found in the increased evaporating power of which it is capable; the number of cubic feet of water evaporated per hour by the "Rocket" was 18-24, whereas by the old engines the number was only 15·92. The increased evaporating power of the new engine was owing to the number of tubes intro 160 IMPROVEMENTS IN LOCOMOTIVE ENGINE. duced into the boiler, presenting a large area of heating surface to the water. Thus the "Rocket" engine, weighing only 4 tons, had an extent of evaporating surface, three times and a half greater than the old engines, which weighed upwards of 7 tons. The great object to be attained in subsequent improvements was, therefore, to increase the evaporating surface; and the additional weight which the new engines were capable of receiving, afforded a valuable means of securing this object. 116. Further Improvements in the Locomotive Engine.— The principal improvements introduced into the locomotive engine, soon after the date of the Liverpool experiments, were of three kinds. 1. The cylinders of the “Rocket” were placed outside the engine; their temperature was consequently reduced by exposure to the atmosphere, and a proportionate amount of heat was lost by the condensation of steam thus produced. In engines subsequently constructed, the cylinders were accordingly placed inside the casing upon which the chimney rested; they were thus exposed to the heated air as it escaped from the flue tubes within the boiler to the chimney, and maintained at the temperature of this air, by which means condensation was prevented. 2. A second improvement consisted in increasing the evaporating surface. The additional weight which the new engines were capable of receiving, was devoted to the enlargement of the boiler, and to an increased number of flue tubes of smaller diameter than those of the "Rocket." In this engine, the number of these tubes was 25, their diameter being three inches; the surface thus exposed to the heated air was 113 square feet. In engines of later construction, the number of tubes has been variously increased: the Meteor had 88 of two inches diameter; the Comet, Arrow, and Dart, 90 of the same diameter; the Northumbrian, 132 of about an inch and a half diameter; and in an engine built by Mr. Robert Stephenson for the Grand Junetion Railway, the number of tubes amounted to 169. The effect of this increase of evaporating surface was immediately |