Carbon stars represent an important group of stars for the study of
 stellar evolution and of mass-loss processes.  Normal carbon stars are
 identified by their optical spectra, but there are a small number of
 known or suspected carbon stars with high mass loss rates, optically
 thick dust shells, and no optical counterparts.  AFGL 3068 is a proto-
 type of this group of objects.  The IRAS Low Resolution Spectrometer
 (LRS) data allowed the identification of about 30 more candidate
 objects based upon comparison with AFGL 3068.

 Unlike the "normal" carbon stars, these "extreme" carbon stars do not
 show the 11.3 micron feature, in emission or in absorption.  It has
 been suggested that the dust is mainly graphite or amorphous carbon in
 the dust shells of these objects.  The identification of the nature of
 dust in the circumstellar shells of the extreme carbon stars, and
 determination of the condition from which such dust is formed,
 would help us to understand why the dust formed in these sources is
 different from that formed in normal carbon stars.  We would like to
 obtain SWS and LWS observations to search for dust features in the
 infrared spectra of a number of extreme carbon star candidates, and
 to define the spectral energy distributions of their dust emission.
 Radiative transfer modeling of the observed spectra
 can then be carried out to derive an empirical opacity function and to
 deduce the mass loss history of these objects.  These
 observations will provide a detailed picture of the dust shell
 properties of these sources which are the most extreme known examples
 of carbon-rich circumstellar envelopes.