15. A sample of coal has the following composition \( \cdot \)
\begin{tabular}{|c|c|}
\hline Per Cent & Per Cent \\
\hline C 739 & \( N \quad 14 \) \\
\hline H 48 & \( \mathrm{H}_{2} \mathrm{O} \quad 54 \) \\
\hline 88 & Ash 57 \\
\hline
\end{tabular}
When the coal was used in a furnace, the ashes contained 18 per cent carbon and the flue gases analyzed 12 per cent free oxygen, dry analysis.
Required: 1. The theoretical requirement of air, in cuble feet per pound of coal
2. The volume of air actually used, and the percentage excess air.
3. The percentage composition of the total flue gases, wet analysis.
