**The analysis of a sample of air from old workings is reported to be O**

_{2}– 19.3%, CO_{2}– 0.4%, N_{2}= 79.8%, CH_{4}– 0.5%. Find the percentage of air and black damp in the sample, as well as composition of black damp.Standard composition is not given. These values can be taken as CO_{2} – 0.03, O_{2} – 20.93 and N_{2} – 79.04 respectively (if not given).

CO_{2} eq = CO_{2} wrt O_{2}

\( = \left( {\frac{{C{O_{2,std}}}}{{{O_{2,std}}}}} \right){O_{2,ret}} = \left( {\frac{{0.03}}{{20.93}}} \right)x19.3\)

= 0.028

N_{2} eq = N_{2} wrt O_{2}

\( = \left( {\frac{{{N_{2,std}}}}{{{O_{2,std}}}}} \right){O_{2,ret}} = \left( {\frac{{79.04}}{{20.93}}} \right)x19.3\)

= 72.88

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