LOCOMOTIVE ENGINES.
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Under this section we shall first treat of the Locomotive properand its Tender, as used on railways; and then notice various formsof Engines used for traction or haulage of machinery and roadtraffic, Portable Engines employed for driving agricultural ma- cliinery , Steam Rollers for roads, &c.
COMBUSTION IN THE LOCOMOTIVE.
THE STEAM BLAST—FIRE-BOX AND COMBUSTION CHAMBER .
The successful development of the locomotive engine has beenmainly due to the introduction of the steam blast, or an applicationof part of the motive power for effecting a rapid and intense com-bustion of the fuel in the fire box of the boiler. This is producedby blowing the waste steam from the cylinders into the chimney,thus causing a partial vacuum, which is filled up by the air rushingthrough the fire box, carrying the flame and heated gases throughthe small tubes placed in the body of the boiler. By this meansthe water is exposed to a number of highly-heated surfaces; thethinness of these tubes adding greatly to their effectiveness in pro-ducing steam. The firebox, however, is un-doubtedly that part ofthe boiler where thewater is boiled morequickly,more especiallyat the top. This is dueto the material of whichitiscomposed—namely,copper — being a verygood conductor, keep-ing quite free from in-crustation, and the con-centrated and intensevertical heat, caused bya due admixture of the oxygen of the atmosphere, forced in ameasure amongst the live fuel. The practical limit to be arrivedat is, that the blast must not be too powerful, so as to lift andcarry off the fuel through the tubes, and then up the chimney