Eq. (2) on page 394 should read

$$ {Q}_{\mathrm{a}}={Q}_{\mathrm{t}}-{Q}_1, $$
(2)
$$ {Q}_{\mathrm{a}}=\varDelta {P}_{\mathrm{pr}}/\left[\upmu \left({X}_1^{\mathrm{H}}+{X}_2^{\mathrm{H}}\right)\right] $$
(3)