LOCOMOTIVE ENGINE. 409 



ments that have been made in them, and the principal variations in construction 

 from other engines. 



The general order of description will be, I. THE BOILER, AND THE MANNER OF 

 GENERATING THE STEAM, with the means of supplying the boiler, of cleaning it out, 

 and of insuring its safety ; also of ascertaining the pressure of the steam, and the 

 quantity of water. 



II. THE CYLINDERS, AND THE MANNER OF USING THE STEAM, with the mode of 

 supplying the cylinders with steam, and working the pistons and slide valves ; and 

 of moving the wheels and propelling the engine. 



III. THE WHEELS, FRAMING, &o, OF THE ENGINE, with the springs, axle boxes, 

 and guides, &c., connected with the frame. 



And IV. THE TENDER, for carrying coke and water to supply the boiler. 



THE BOILER, AND THE MANNER OF GENERATING THE STEAM. 



The boiler consists of several distinct parts ; the cylindrical portion A called 

 peculiarly the boiler, the external fire-box B communicating with it, the internal 

 fire-box C, containing the fire-grate D, and the tubes E communicating between 

 the internal fire-box and the smoke-box F, upon which is fixed the chimney G. 



THE BOILER AA (Plates LXXXIX. and CX.) is a cylinder 7 feet 6 inches long, 

 and 3 feet 6 inches in diameter outside ; it is made of wrought iron plates five-six- 

 teenths of an inch thick, lapping over each other, and joined together by iron 

 rivets seven-eighths of an inch in diameter and If inches apart, as shown at A 

 in fig. 5, which is a section of a joint, half 

 size. The rivets are inserted red hot and 

 contract in cooling, drawing the plates 

 forcibly together, and making a very close 

 joint. 



The boiler is covered with wood aa (Plate XC.) one inch thick, put on in longi- 

 tudinal staves, and bound round by the iron hoops bb, Plates LXXXIX. and CX., 

 which are screwed together at the bottom ; this casing of wood is for the purpose 

 of retaining the heat, and preventing it from being carried off by the air when 

 moving rapidly through it, wood being an imperfect conductor of heat. 



THE EXTERNAL FiRE-Box B B is a box nearly square, 4 feet wide outside, and 

 3 feet TTJ inches long in the direction of the boiler, made of wrought iron plates 

 five- sixteenths of an inch thick, like those of the boiler ; the bottom is 2 feet 1 inch 

 below the boiler, and the upper part is a semi-cylinder, concentric with the boiler, 

 as shown in the cross section, fig. 2, Plate XCII. The fire box is open at the 

 bottom, and has a circular opening cut in the front side, of the same size as 



