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Using a sample of 10 billion $J/{\psi}$ events collected with the BESIIIdetector, the decays $\eta' \to \pi^{+}\pi^{-}\pi^{+}\pi^{-}$, $\eta' \to\pi^{+}\pi^{-}\pi^{0}\pi^{0}$ and $\eta' \to 4 \pi^{0}$ are studied via theprocess $J/{\psi}\to\gamma\eta'$. The branching fractions of $\eta' \to\pi^{+}\pi^{-}\pi^{+}\pi^{-}$ and $\eta' \to \pi^{+}\pi^{-}\pi^{0}$ $\pi^{0}$are measured to be $( 8.56 \pm 0.25({\rm stat.}) \pm 0.23({\rm syst.}) ) \times{10^{ - 5}}$ and $(2.12 \pm 0.12({\rm stat.}) \pm 0.10({\rm syst.})) \times{10^{ - 4}}$, respectively, which are consistent with previous measurements butwith improved precision. No significant $\eta' \to 4 \pi^{0}$ signal isobserved, and the upper limit on the branching fraction of this decay isdetermined to be less than $1.24 \times {10^{-5}}$ at the $90\%$ confidencelevel. In addition, an amplitude analysis of $\eta' \to\pi^{+}\pi^{-}\pi^{+}\pi^{-}$ is performed to extract the doubly virtualisovector form factor $\alpha$ for the first time. The measured value of$\alpha=1.22 \pm 0.33({\rm stat.}) \pm 0.04({\rm syst.})$, is in agreement withthe prediction of the VMD model.

Improved measurement of the decays $\eta' \to \pi^{+}\pi^{-}\pi^{+(0)}\pi^{-(0)}$ and search for the rare decay $\eta' \to 4\pi^{0}$