  The ${\rm H_{5}S_{2}}$ and ${\rm H_{2}S}$ compounds are the two candidates
for the low-temperature phase of compressed sulfur-hydrogen system. We have
shown that the value of Coulomb pseudopotential ($\mu^{\star}$) for ${\rm
H_{5}S_{2}}$ ($\left[T_{C}\right]_{\rm exp}=36$~K and $p=112$~GPa) is
anomalously high. The numerical results give the limitation from below to
$\mu^{\star}$ that is equal to $0.402$ ($\mu^{\star}=0.589$, if we consider the
first order vertex corrections to the electron-phonon interaction). Presented
data mean that the properties of superconducting phase in the ${\rm
H_{5}S_{2}}$ compound can be understood within the classical framework of
Eliashberg formalism only at the phenomenological level ($\mu^{\star}$ is the
parameter of matching the theory to the experimental data). On the other hand,
in the case of ${\rm H_{2}S}$ it is not necessary to take high value of Coulomb
pseudopotential to reproduce the experimental critical temperature relatively
well ($\mu^{\star}=0.15$). In our opinion, ${\rm H_{2}S}$ is mainly responsible
for the observed superconductivity state in the sulfur-hydrogen system at low
temperature.
