The normality of orthophosphoric acid having purity of 70 % by weight and specific gravity 1.54 is :

Equivalent weight of orthophosphoric acid (H₃PO₄) = $=\frac{3+31+64}{3}=\frac{98}{3}$
Now 100 g solution contains 70 g H₃PO₄
$\frac{100}{1000\times 1.54}$ litre of solution contains $\frac{70}{98/3}$ g equivalent of H₃PO₄
Normality solution = $=\frac{\frac{70\times 3}{98}}{\frac{1}{10\times 1.54}}=\frac{70\times 3}{98}\times 10\times 1.54=33\mathrm{N}$