  Small flares frequently occur in the quiet Sun. Previous studies have noted
that they share many common characteristics with typical solar flares in active
regions. However, their similarities and differences are not fully understood,
especially their thermal properties. In this study, we performed imaging
spectroscopic observations in the H$\alpha$ line taken with the Solar Dynamics
Doppler Imager on the Solar Magnetic Activity Research Telescope (SMART/SDDI)
at the Hida Observatory and imaging observations with the Atmospheric Imaging
Assembly onboard Solar Dynamics Observatory (SDO/AIA). We analysed 25 cases of
small flares in the quiet Sun over the thermal energy range of
$10^{24}-10^{27}\,\mathrm{erg}$, paying particular attention to their thermal
properties. Our main results are as follows: (1) We observe a redshift together
with line centre brightening in the H$\alpha$ line associated with more than
half of the small flares. (2) We employ differential emission measure analysis
using AIA multi-temperature (channel) observations to obtain the emission
measure and temperature of the small flares. The results are consistent with
the Shibata & Yokoyama (1999, 2002) scaling law. From the scaling law, we
estimated the coronal magnetic field strength of small flares to be 5 --15 G.
(3) The temporal evolution of the temperature and the density shows that the
temperature peaks precede the density peaks in more than half of the events.
These results suggest that chromospheric evaporations/condensations play an
essential role in the thermal properties of some of the small flares in the
quiet Sun, as does for large flares.
