  We present the results of an observational study of the efficiency of deep
mixing in globular cluster red giants as a function of stellar metallicity. We
determine [C/Fe] abundances based on low-resolution spectra taken with the Kast
spectrograph on the 3m Shane telescope at Lick Observatory. Spectra centered on
the 4300 Angstrom CH absorption band were taken for 42 bright red giants in 11
Galactic globular clusters ranging in metallicity from M92 ([Fe/H]=-2.29) to
NGC 6712 ([Fe/H]=-1.01). Carbon abundances were derived by comparing values of
the CH bandstrength index S2(CH) measured from the data with values measured
from a large grid of SSG synthetic spectra. Present-day abundances are combined
with theoretical calculations of the time since the onset of mixing, which is
also a function of stellar metallicity, to calculate the carbon depletion rate
across our metallicity range. We find that the carbon depletion rate is twice
as high at a metallicity of [Fe/H]=-2.3 than at [Fe/H]=-1.3, which is a result
qualitatively predicted by some theoretical explanations of the deep mixing
process.
