  We present a combined near-infrared and molecular-line study of 25' x 8' area
in the Northern streamer of the IC 5146 cloud. Using the technique pioneered by
Lada et al 1994, we construct a Gaussian smoothed map of the infrared
extinction with the same resolution as the molecular line observations in order
to examine correlations of integrated intensities and molecular abundances with
extinction for C17O, C34S, and N2H+. We find that over a visual extinction
range of 0 to 40 magnitudes, there is good evidence for the presence of
differential gas-phase depletions in the densest portions of IC 5146. Both CO
and CS exhibit a statistically significant (factor of ~3) abundance reduction
near Av ~ 12 magnitudes while, in direct contrast, at the highest extinctions,
Av > 10 magnitudes, N2H+ appears relatively undepleted. Moreover, for Av < 4
magnitudes there exists little or no N2H+. This pattern of depletions is
consistent with the predictions of chemical theory.
