  Intermetallic silicide compounds, LaScSi and Y$_5$Si$_3$, known for being
hydrogen (H) storage materials, are drawing attention as candidates for
electrides in which anions are substituted by unbound electrons. It is inferred
from a muon spin rotation experiment that the local field at the muon site
(which is the same site as that for H) in these compounds exhibits a large
negative shift under an external magnetic field, which is mostly independent of
temperature. Such anomalous diamagnetism signals a unique property of electride
electrons associated with transition metals. Moreover, the diamagnetic shift
decreases with increasing H content, suggesting that the electride electrons
existing coherently in the hollow interstitial positions are adsorbed by H to
form hydride ions (H$^-$)
