(the specific gravity of spirit is $0.8.)$
Height of the spirit column, $h_{2}=12.5+15=27.5 cm$
Density of water, $\rho_{1}=1 g cm ^{-3}$
Density of spirit, $\rho_{2}=0.8 g cm ^{-3}$
Density of mercury $=13.6 g cm ^{-3}$
Let $h$ be the difference between the levels of mercury in the two arms.
Pressure exerted by height $h,$ of the mercury column:
$=h \rho g =h \times 13.6 g \ldots(i)$
Difference between the pressures exerted by water and spirit:
$=h_{1} \rho_{1} g -h_{1} \rho_{1} g$
$=g(25 \times 1-27.5 \times 0.8)=3 g \ldots (i i)$
Equating equations ( $i$ ) and (ii), we get:
$13.6 hg =3 g h$
$=0.220588 \approx 0.221 cm$
Hence, the difference between the levels of mercury in the two arms is $0.221 \,cm .$


$d_{1}=5\, cm , V_{1}=4\, cm , d_{2}=2\, cm , V_{2}=?$