Ferric chloride is applied to stop bleeding because -

$\displaystyle \mathrm{FeCl}_3$ reacts with the constituents of blood which is a positively charged sol.

$\displaystyle \mathrm{Cl}^{-}$ions cause coagulation of blood.

$\displaystyle \mathrm{Fe}^{3+}$ ions coagulate blood which is a negatively charged sol.

Blood absorbs $\displaystyle \mathrm{FeCl}_3$ and forms a complex.