  Classical chemical analyses may be affected by systematic errors that would
cause observed abundance differences between dwarfs and giants. For some
elements, however, the abundance difference could be real. We address the issue
by observing 2 solar--type dwarfs in NGC 5822 and 3 in IC 4756, and comparing
their composition with that of 3 giants in either of the aforementioned
clusters. We determine iron abundance and stellar parameters of the dwarf
stars, and the abundances of calcium, sodium, nickel, titanium, aluminium,
chromium, silicon and oxygen for both the giants and dwarfs. We acquired UVES
high-resolution, of high signal--to--noise ratio (S/N) spectra. The width of
the cross correlation profiles was used to measure rotation velocities. For
abundance determinations, the standard equivalent width analysis was performed
differentially with respect to the Sun. For lithium and oxygen, we derived
abundances by comparing synthetic spectra with observed line features. We find
an iron abundance for dwarf stars equal to solar to within the margins of error
for IC 4756, and slightly above for NGC 5822 ([Fe/H]= 0.01 and 0.05 dex
respectively). The 3 stars in NG 4756 have lithium abundances between Log N(Li)
2.6 and 2.8 dex, the two stars in NGC 5822 have Log N(Li) ~ 2.8 and 2.5,
respectively. For sodium, silicon, and titanium, we show that abundances of
giants are significantly higher than those of the dwarfs of the same cluster
(about 0.15, 0.15, and 0.35 dex).
