550 



THE STEAM-ENGINE. 



Pig. 77. 



which any water which may collect in the cylinder by condensation or priming 

 may be discharged. A cock r', fig. 67, communicating with a small tube proceed- 

 ing from the branches of the waste pipe _p', fig. 74, is likewise provided to 

 discharge from that pipe any water which may be collected in it. After the 

 steam has been admitted to work the piston through the slide-valve, and has 

 been discharged through the waste-port by shifting that valve, it passes through 

 the pipe p' into the blast-pipe p, from the mouth of which it issues, with great 

 force, up the funnel G. When the motion of the engine is rapid, the steam 

 from the two cylinders proceeds in an almost uninterrupted current from the 

 blast-pipe, and causes a strong draught up the chimney. The heated air 

 which passes from the mouths of the tubes into the smoke-box is drawn up by 

 this current, and a corresponding draught is produced in the fire-box. 



The piston-rods Y terminate in a fork, by which they are attached to cross 

 heads Z, the ends of which are confined by guide-bars A 7 , in which they are 

 allowed to play backward and forward through a space equal to the stroke of 

 the piston. To these cross heads Z, between the prongs of the fork in which 

 the piston terminates, are attached the foremest ends of the connecting rods 

 B'. These rods are, therefore, driven backward and forward by the motion 

 imparted to the cross head Z by the piston-rods Y. The connecting rods B' 

 are attached at the hinder ends to two cranks formed upon the axles C' of the 

 driving wheels D x . These two cranks are formed upon the axles precisely at 

 right angles to each other. The left-hand crank is represented in its hori- 

 zontal position, in fig. 69, and the right-hand crank is 

 seen in its vertical position. A cranked axle is repre- 

 sented on a larger scale in fig. 77, and the two cranks 

 are seen in a position oblique to the plane of the figure. 

 As this axle is the instrument by which the impelling 

 force is conveyed to the load, and as it has to support a 

 great portion of the weight of the engine, it is constructed 

 with great strength and precision. It is made all in one 

 piece, and of the best wrought iron called bacfc barrow, 

 or scrap iron. In the engine here described its extreme 

 length is six feet and a half, and its diameter is five 

 inches. At the centre part A it is cylindrical, and is 

 increased to five inches and a quarter at C, where the 

 cranks are formed. The sides D of the cranks are four 

 inches thick, and the crank pins B, which are truly cyl- 

 indrical, are five inches diameter, and three inches in 

 length, the brasses at the extremities of the connecting 

 rods which play upon them having a corresponding 

 magnitude. The distance from the centre of the crank- 

 pins B to the centre of the axle A must be exactly equal I 

 to half the stroke of the piston, and is, therefore, in this j 

 case precisely nine inches. Upon the parts F, which 

 are seven inches and a half long, the great driving 

 wheels are firmly fastened, so as to be prevented from 

 turning or shaking upon the axle. The axle projects 

 beyond the wheels at G, where it is reduced to three 

 inches and an eighth diameter. These projecting parts 

 G are five inches long, having collars at the outer ends. 

 Brasses are fixed at the outside frame of the engine 

 which rest upon these projections G of the axle, and 

 upon these brasses the weight of the engine is supported. 

 The entire axle is accurately turned in a lathe, and each 



