  We have observed Feshbach resonances in elastic collisions between ultracold
${}^{52}$Cr atoms. This is the first observation of collisional Feshbach
resonances in an atomic species with more than one valence electron. The zero
nuclear spin of ${}^{52}$Cr and thus the absence of a Fermi-contact interaction
leads to regularly-spaced resonance sequences. By comparing resonance positions
with multi-channel scattering calculations we determine the s-wave scattering
length of the lowest $^{2S+1}\Sigma_{g}^{+}$ potentials to be
$\unit[112(14)]{a_0}$, $\unit[58(6)]{a_0}$ and $-\unit[7(20)]{a_0}$ for S=6, 4,
and 2, respectively, where $a_{0}=\unit[0.0529]{nm}$.
