  We present an up-to-date catalog of intrinsic iron abundance spreads in the
55 Milky Way globular clusters for which sufficiently precise spectroscopic
measurements are available. Our method combines multiple datasets when possible
to improve the statistics, taking into account the fact that different methods
and instruments can lead to systematically offset metallicities. Only high
spectral resolution (R>14,000) studies that measure the equivalent widths of
individual iron lines are found to have uncertainties on the metallicities of
the individual stars that can be calibrated sufficiently well for the intrinsic
dispersion to be separated cleanly from random measurement error. The median
intrinsic iron spread is found to be 0.045 dex, which is small but
unambiguously measured to be non-zero in most cases. There is large variation
between clusters, but more luminous globular clusters, above 10^5 L_sun, have
increasingly large iron spreads on average; no trend between iron spread and
metallicity is found.
