  We investigate the spectrum of the partial transpose (negativity spectrum) of
two adjacent regions in gapped one-dimensional models. We show that, in the
limit of large regions, the negativity spectrum is entirely reconstructed from
the entanglement spectrum of the bipartite system. We exploit this result in
the XXZ spin chain, for which the entanglement spectrum is known by means of
the corner transfer matrix. We find that the negativity spectrum levels are
equally spaced, the spacing being half that in the entanglement spectrum.
Moreover, the degeneracy of the spectrum is described by elegant combinatorial
formulas, which are related to the counting of integer partitions. We also
derive the asymptotic distribution of the negativity spectrum. We provide exact
results for the logarithmic negativity and for the moments of the partial
transpose. They exhibit unusual scaling corrections in the limit $\Delta\to1^+$
with a corrections exponent which is the same as that for the R\'enyi
entropies.
