e conditions hold only for the perfect
combustion of a pound of pure carbon.

Carbon monoxide (CO) produced by the imperfect combustion of carbon,
will occupy twice the volume of the oxygen entering into its composition
and will increase the volume of the flue gases over that of the air
supplied for combustion in the proportion of

100 + the per cent CO / 2
1 to -------------------------
100

When pure carbon is the fuel, the sum of the percentages by volume of
carbon dioxide, oxygen and one-half of the carbon monoxide, must be in
the same ratio to the nitrogen in the flue gases as is the oxygen to the
nitrogen in the air supplied, that is, 20.91 to 79.09. When burning
coal, however, the percentage of nitrogen is obtained by subtracting the
sum of the percentages by volume of the other gases from 100. Thus if an
analysis shows 12.5 per cent CO_{2}, 6.5 per cent O, and 0.6 per cent
CO, the percentage of nitrogen which ordinarily is the only other
constituent of the gas which need be considered, is found as follows:

100 - (12.5 + 6.5 + 0.6) = 80.4 per cent.

The action of the hydrogen in the volatile constituents of the fuel is
to increase the apparent percentage of the nitrogen in the flue gases.
This is due to the fact that the water vapor formed by the combustion of
the hydrogen will condense at a temperature at which the analysis is
made, while the nitrogen which accompanied the oxygen with which the
hydrogen originally combined maintains its gaseous form and passes into
the sampling apparatus with the other gases. For this reason coals
containing high percentages of volatile matter will produce a larger
quantity of water vapor, and thus increase the apparent percentage of
nitrogen.

Air Required and Supplied--When the ultimate analysis of a fuel is
known, the air required for complete combustion with no excess can be
found as shown in the chapter on combustion, or from the following
approximate formula:

Pounds of air required per pound of fuel =

(C O S)
34.56 (- + (H - -) + -)[29] (11)
(3 8 8)

where C, H and O equal the percentage by weight of carbon, hydrogen and
oxygen in the fuel divided by 100.

When the flue gas analysis is known, the total, amount of air supplied
is:

Pounds of air supplied per pound of fuel =

N
3.036 (-----------) x C[30] (12)
CO_{2} + CO

where N, CO_{2