4 
Steam Engine. 
rent occasioned by the rarefaction produced in the glass 
chimney. That this is a true account of the process, any 
one may satisfy himself, by closing the apertures of the 
grating at the bottom of the lamp, through tvhich the air 
ascends up the chimney ; and the wick no longer supplied 
with the oxygen of the atmosphere, will send olF the com- 
bustible oil, unburnt in the form of smoke like a common 
lamp. 
If a piece of wood be distilled, it furnishes an acidu- 
lous watery liquor, a large quantity of carburetted hydro- 
gen gas, that is charcoal dissolved in hydrogen gas, and 
its own bulk of charcoaL Both the hydrogen gas and 
the charcoal, are combustible with access of air, but in- 
combustible without it. The flame of a wood fire, is ow- 
ing to the ascension of the carburetted hydrogen distilled 
off* from the wood. The smoke is partly acidulous va- 
pour, and partly unconsumed carburetted hydrogen. 
Whatever is capable of being burnt gives out heat : 
for the oxygen of the atmosphere, when it combines with 
a combustible body, parts with the heat to which it is che- 
mically united. That heat, becomes sensible, and acts 
upon the bodies around. The smoke attaches itself to 
the bodies it meets with, and sticks to them, and a quan- 
tity of carbon or charcoal is deposited : this mixture is 
called Soot. 
When a quantity of coal is set on fire the same process 
takes place ; a tar-acid vapour flies oflf mixed with carbu- 
retted hydrogen holding much carbon or charcoal in solu- 
tion ; this is the smoke, which when condensed in the 
chimney or on the bottom ^ a boiler, forms also soot ; 
thicker, and containing more carbon, and volatile oil than 
the soot of wood. 
Four ounces avoirdupois of pine saw dust, yielded me 
12 quarts of carburetted h 3 ^drogen. The same weight of 
bituminous Liverpool coal, yielded me 18 quarts. Some 
