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.