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THE STEAM-ENGIKE. 



(FOURTH LECTURE.) 



The machinery which has been explained, consisting of the 

 its passages and valves, the 

 and crank, together with the 



by which the mechanical effect developed by the furnace and the boiler 

 to the working point and so modified as to be adapted to the 

 uses to which the machine is applied. The boiler is at once a magazine in 

 which the moving power, is stored in sufficient quantity to supply the riimindi 

 of the engine and an apparatus in which that power is fabricated The me- 

 chanical effect evolved in the conversion of water into steam by heat, is the 

 process by which the power of the steam-engine is p roduced, and space is 

 provided in the boiler, capacious enough to contain as much steam as is neees- 



undiimaishrd, notwithstanding the constant drafts made upon it by the cylin- 

 der : even the water itself, from the evaporation of which the 

 power is produced, ought to be regarded as an instrument by which the 

 of the heat of the combustible is rendered mechanically efficient, masmuch as 

 the same heat, applied not only to other liquids but even to solids, would like- 

 wise be productive of mechanical effects. The boiler and its furnace are 



are entitled to especial attention. 



Coax, the combustible almost universally used in steam-engines, is a 

 stance, the principal constituents of which are 



ry mixed with sulphur in a small p ro porti on, 



In different sorts of coal the proportions of these 



of good quality about three quarters of the whole weight of dm 



When carbon is heated to a temperature of about 70CP in 



