  As part of a reanalysis of galactic Asymptotic Giant Branch (AGB) stars at
infrared (IR) wavelengths, we discuss a sample (357) of carbon stars for which
mass loss rates, near-IR photometry and distance estimates exist. For 252
sources we collected mid-IR fluxes from the MSX (6C) and the ISO-SWS
catalogues. Most stars have spectral energy distributions up to 21 microns, and
some (1/3) up to 45 microns. This wide wavelength coverage allows us to obtain
reliable bolometric magnitudes. The properties of our sample are discussed with
emphasis on about 70 stars with astrometric distances. We show that mid-IR
fluxes are crucial to estimate the magnitude of stars with dusty envelopes. We
construct HR diagrams and show that the luminosities agree fairly well with
model predictions based on the Schwarzschild's criterion, contrary to what is
widely argued in the literature. A problem with the brightness of C stars does
not appear to exist. From the relative number of Mira and Semiregular
C-variables, we argue that the switch between these classes is unlikely to be
connected to thermal pulses. The relevance of the two populations varies with
the evolution, with Miras dominating the final stages. We also analyze mass
loss rates, which increase for increasing luminosity, but with a spread that
probably results from a dependence on a number of parameters (like e.g.
different stellar masses and different mechanisms powering stellar winds).
Instead, mass loss rates are well monitored by IR colours, especially if
extended to 20 microns and beyond, where AGB envelopes behave like black
bodies. From these colours the evolutionary status of various classes of C
stars is discussed.
