2 x 2 = 136.4); so that above those critical
temperatures, the heat of combustion of acetylene is only 315.7 - (69.0 +
136.4) = 110.3. [Footnote: When the heat of combustion of acetylene is
quoted as 315.7 calories, it is understood that the water formed is
condensed into the liquid state. If the water remains gaseous, as it must
do in a flame, the heat of formation is reduced by about 10 calories.
This does not affect the above calculation, because the heat of
combustion of hydrogen when the water remains gaseous is similarly 10
calories less than 69, _i.e._, 59, as mentioned above in the text.
Deleting the heat of liquefaction of water, the calculation referred to
becomes 305.7 - (59.0 + l36.4) = 110.3 as before.] This value of 110.3
calories is clearly made up of the heat of formation of acetylene itself,
and twice the heat of conversion of carbon into carbon monoxide,
_i.e._, for diamond carbon, 58.1 + 26.1 x 2 = 110.3; or for
amorphous carbon, 52.1 + 29.1 x 2 = 110.3. From the foregoing
considerations, it may be inferred that the acetylene-oxygen blowpipe can
be regarded as a device for burning gaseous carbon in oxygen; but were it
possible to obtain carbon in the state of gas and so to lead it into a
blowpipe, the acetylene apparatus should still be more powerful, because
in it the temperature would be raised, not only by the heat of formation
of carbon monoxide, but also by the heat attendant upon the dissociation
of the acetylene which yields the carbon.
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