We propose to search for dust emission toward a representative
 sample of galaxy clusters with cooling flows.
 The reason for selecting clusters with reported cooling flows is
 that these are where a neutral intergalactic medium should be
 present, if the cooling flow interpretation is correct.  Our
 goal is to detect the dust so we propose observations with the
 ISOPHOT PHT-C at 160 microns.  Not only does this wavelength
 correspond well with the expected temperatures but is also
 the most sensitive available.  These sources have been selected
 for their proximity and reported mass inflow rate in order to
 provide the most sensitive test possible.  All of the proposed
 sources have already been observed by us in CO(1-0) and CO(2-1).
 HI observations have also been published for all of these sources.

 Our goal is to determine whether the reddening due to intergalactic
 but intracluster dust reported by, in particular, Hu et al.
 (1992) is real.  The proposed observations can answer this
 question with no ambiguity.  The dust temperature MUST fall within
 a range observable with the 160 micron filter.  The issue of
 reddening is very important for studies of galaxies in the cluster
 environment because it would create a systematic color gradient
 along the line of sight through the intracluster material.

 These observations also provide a test for cooling flow models
 with dust. It has been suggested that the non-detections of molecules
 in cooling flows (ALL except NGC 1275) could be due to the molecules
 condensing onto dust grains.  If so, we should clearly detect this
 dust.