\( 20 \,\text{mL} \) of \( 0.5 \,\text{M} \) \( \text{NaCl} \) is required to coagulate \( 200 \,\text{mL} \) of \( \text{As}_2\text{S}_3 \) solution in \( 2 \) hours. The coagulating value of \( \text{NaCl} \) is __________.