  We derive a mean attenuation curve out to the rest-frame extreme ultraviolet
(EUV) for 'BAL dust' - the dust causing the additional extinction of active
galactic nuclei (AGNs) with broad absorption lines (BALQSOs). In contrast to
the normal, relatively flat, mean AGN attenuation curve, BAL dust is well fit
by a steeply rising, SMC-like curve. We confirm the shape of the theoretical
Weingartner & Draine SMC curve out to 700 Angstroms but the drop in attenuation
at still shorter wavelengths is less than predicted. The similar SMC-like
attenuation curve for low-ionization BALQSOs (LoBALs) does not support the idea
that they are an early phase in the life of an AGN when it is breaking out of a
cocoon of star-forming dust. Although the attenuation is only E(B - V) ~ 0.03 -
0.05 in the optical, it rises to one magnitude in the EUV, which is an optimum
value for radiative acceleration of dusty gas. Because the spectral energy
distribution of AGNs peaks in the EUV, the force on the dust dominates the
acceleration of BAL gas. Although the shape of the attenuation curve for LoBALs
is similar to the shape for HiBALs, the LoBALs on average show negative
attenuation in the optical. This is naturally explained if there is more light
scattered into our line of sight in LoBALs compared with non-BALQSOs. We
suggest that this and partial covering are causes when attenuation curves
appear to be steeper in the UV than an SMC curve.
