LOCOMOTIVE ENGINE. 423 



an hour and three quarters on an average, and requires the consumption of about one 

 and a half or two cwt. of coke ; in some places the boiler and tender are supplied 

 with hot water by means of a stationary boiler, in order to expedite the getting up of 

 the steam, and also as a means of economy. 



The area of the fire-grate is 9^ square feet; it is 18 inches below the bottom of 

 the lowest tubes, and the space for the fire when quite filled up to the tubes is 14 

 cubic feet, and holds about 2^ cwt. of coke ; but the fire-box is not always filled so 

 full as this, and usually contains about one and a half or two cwt. 



The surface of water exposed to the heat directly radiated from the fire is the 

 whole surface of the internal fire-box, deducting the fire-door and the tubes, and is 

 equal to 50 square feet ; and that exposed to the current of hot air, or conducted heat, 

 is the interior surface of the tubes, and is equal to 432 square feet. The surface 

 exposed to radiated heat is considerably more efficacious in generating steam than 

 that exposed to conducted heat only, as the supply of heat is more copious, and the 

 proportion was found to be about three times in an experiment tried by Mr. Stephen- 

 son, which is the only one that has been made upon the subject ; the experiment was 

 made with an old engine and the proportion may be somewhat different in the mo- 

 dern engines. 



The area of passage for the heated air from the fire-box to the chimney is the 

 sectional area of all the tubes inside the ferrules ; the ferrules are three eighths of an 

 inch less than the outside of the tubes, and are therefore an inch and a quarter in diame- 

 ter inside; and the sectional area of them all, (124 in number,) is T06 square feet. 

 The area of the passage through the chimney is rather more, or T23 feet. 



In the Rocket engine the area of passage through the tubes was '90 square feet or 

 nearly the same as in this engine, though the fire-grate was but half the size ; but 

 the heating surface of the tubes was only one third, from the large size and small 

 number of the tubes ; the heating surface of the fire-box was also only three quarters 

 of that of the present engine. 



In the old engines before the Rocket, the area of passage through the flue was 

 two and a half times the size, but the heating surface was only one thirteenth of 

 that in the present engine; the fire-box had also only one fifth of the heating surface; 

 the fire-grate was three quarters of the size. 



THE CYLINDERS AND THE MANNER OF USING THE STEAM. 



STEAM PIPE. SS, (Plates XC. and XCII.,) is the steam pipe for conveying the 

 steam from the boiler to the cylinder where it is to be used ; it is made of copper 

 three sixteenths of an inch thick, and the part within the boiler is 5 inches' diameter in- 

 side ; it passes through the tube plate of the smoke-box and is bolted to it by a flanch. 

 The pipe then divides into two smaller ones, 3| inches in diameter, which pass down 



