Steam Ejigine. 5 
coal would }ueld 24 quarts. Soot then consists cbieily of 
unbiirnt charcoal. 
Take out of the fire, a piece of charcoal about an inch 
or half an inch long, well lighted at one end. You may 
hold it in your fingers, and even excite by blowing, the 
lighted end, without being burnt. Charcoal therefore is 
a very had conductor of heat. Take a piece oi iron or 
brass, a foot long, and holding it at one end, thrust the other 
into the fire. Long before it approaches a red hear, your 
fingers will be burnt. Metals therefore are very good con- 
ductors of heat. Hence, when we sufier soot to accumu- 
late at the bottom of our boilers, we exchange a very good 
for a very bad conductor of heat ; and we must employ 
more fuel, for the purpose of communicating the same 
heat to the water. Hence it is a point of economy to con- 
sume the smoke under the boiler of a steam engine. 
The method of consuming the smoke of furnaces, >cle- 
pends upon two principles : 1st. the vivid, well-lighted 
coals, are pushed forward, and the half lighted coals are 
not thrown upon or beyond them promiscuously, but pla- 
ced at that part of tlie fire, where the body of vivid coals 
commences : hence the smoke arising from the half-light- 
ed, can be made to pass over the lighted coals. But the 
smoke would rise up, if it were not, 21y. that a current of 
air is admitted, and directed downward, so as to drive the 
rising smoke upon and over the surface of the red hot coals, 
where it is burnt and consumed as fuel. 
Suppose the door frame of the fire place, shuts against 
a platform, not level with the fire as usually is the case, 
but raised above the burning fuel, &c. slanting downward 
from the inside of the door toward the fire ; so that the 
coals can be easily pushed inward to any part of the fire ; 
if then, there be a slit of an inch wide for instance, across 
the door, a current of air will pass through that slit over 
the fire in addition to tlie current of air that passes iipv/ards 
