  HST archival FOS spectra of 40 QSOs with z <= 0.5 in the Bright Quasar Survey
have been analyzed. The spectra cover the region 1800-2000 A in the QSOs' rest
frames, including the Al III 1859, Si III] 1892, C III] 1909, and Fe III UV34
emission-lines. We measured the flux of these UV emission-lines, and analyzed
the correlations among UV and optical (H beta, Fe II, and [O III])
emission-line properties as well as soft X-ray photon indices. We found a
significant correlation between Si III]/C III] and Fe II/H beta.
  Si III and C III have similar ionization potentials, but Si III] has one
order magnitude larger critical density than C III]. Si III]/C III] is thus a
density indicator and becomes larger when density is higher. The correlation
between Si III]/C III] and Fe II/H beta indicates that optical Fe II becomes
strong when the density of the broad line region becomes high.
  Our correlation analysis shows that large Si III]/C III] associates with weak
[O III] 5007, large soft X-ray photon index, and narrow H beta width as well as
with large Fe II/H beta. Our results support the previous suggestions that the
density of the broad line region gas and the mass accretion rate govern this
correlation.
