  We present X-ray spectra obtained with BeppoSAX (Satellite per Astronomia X)
of 10 BL Lac objects, selected from the Einstein Medium Sensitivity and Slew
Surveys. We find that in about half of the objects a fit in the 0.1-10 keV
range with a single power law and free absorption yields values of NH larger
than the Galactic ones. In most of these cases, however, broken power law fits
with NH fixed at the Galactic values yield an alternative, better description
of the data and indicate a steepening of the spectrum with increasing energy.
One object (1ES1101-232) is detected up to ~100 keV. Its spectral energy
distribution (SED) peaks in the medium energy X-ray band. For each object we
compute the peak frequency of the SED from multifrequency data. The spectral
indices alpha_x in the 2-10 keV band (Fnu prop to nu^{-alpha_x}) are smaller
(i.e. flatter spectrum) for objects with higher peak frequencies. We therefore
confirm and extend to higher energies the behavior already known for X-ray
selected BL Lac objects in the ROSAT band. We do not find spectral indices
smaller than 1; however, the flat distribution of alpha_x and the correlation
between alpha_x and peak frequency found from our data suggest that a number of
objects may exist, which in the quiescent status have flatter spectrum and peak
frequency in the hard X-ray range.
