  We present a new optical transmission spectrum of the hot Jupiter HAT-P-1b
based on two transits observed with the Double Spectrograph (DBSP) on the
Palomar 200-inch (P200) telescope. The DBSP transmission spectrum, covering a
wavelength range from 3250 to 10007 \r{A}, is consistent with that observed
with the Hubble Space Telescope (HST), but the former has a finer spectral
resolution. The DBSP spectrum alone reveals the presence of a pressure
broadened line wing for Na, the line cores for both Na and K, and tentative
evidence for H$_2$O. We obtain consistent results from the spectral retrieval
analyses performed on the DBSP-only dataset and the DBSP, HST, and Spitzer
combined dataset. Our retrievals suggest a mostly clear atmosphere for
HAT-P-1b, with a cloud coverage of $22^{+5}_{-3}$% that is dominated by
enhanced haze. We derive subsolar abundances for Na, K, and C, and
subsolar-to-solar for O. Future observations with James Webb Space Telescope
and ground-based high-resolution spectrographs should be able to not only
confirm the presence of these species but also stringently constrain the
formation and migration pathways for HAT-P-1b.
