From the early days of infrared observations it has been known that the
 planetary nebulae (PNs) have significant dust emission in the far-
 infrared.  For well observed IRAS sources on the average about 30% of
 the total bolometric flux of PNs comes from the dust component.  It is
 clear that the circumstellar dust is the remnant of the dust shell from
 the preceding red giant phase, but there is considerable uncertainty
 about where the dust emission is coming from because it has been argued
 that the dust will be destroyed on short time scales in the ionized
 region while observations suggest that the dust is mixed into the
 ionized region.  Studies of a few carbon-rich PNs have indicated that
 the dust to gas mass ratio is smaller in PNs than in carbon stars or
 the interstellar medium.  However the depletion of Ca and some other
 refractory elements suggests that the dust cannot be destroyed.  It
 might be ejected from the ionized zone by radiation pressure.

 It is desirable to study the dust in PNs to understand its properties
 and try to resolve these questions.  One aspect of this is the
 proposal to image some PNs in dust emission to see if the dust is in
 the ionized region.  In this proposal we seek detailed spectroscopy
 of the dust emission in selected PNs with strong dust emission.  The
 spectral information which the SWS and LWS instruments can provide
 will for the first time fully characterize the dust emission in these
 PNs.  Using radiative transfer and photoionization models of the dust
 and nebular emission should allow us to deduce the radial temperature
 distribution of the dust and find the dust to gas mass ratios for
 these objects.  We wish to study young PN with the UIE features and
 sources with silicate dust to compare with the older PNs studied
 previously in the literature.  In particular no disk PN with strong
 silicate dust emission has previously been studied in this manner,
 so this project will fill a gap in our knowledge of these objects.