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: