Based on IRAS images, we have selected a sample of dense clouds
 with regular IR morphology and well defined cold cores. The cores
 have been identified by their strong 100 micron emission and lack
 of any 60 micron emission. We want to map these clouds in the far-IR
 with full ISO resolution at the longest ISOPHOT wavelengths. These
 observations provide unique data to address the following aims:

 (1) to study the structure of clouds in the very high density regions
 which are normally only observable in molecular transitions at radio
 and mm wavelengths.

 (2) to refine the estimate of the far IR mass absorption coefficient
 to constrain proposed dust models. The mass absoption coefficient
 is still highly uncertain in dense regions, improvement will also
 serve the interpretation of other ISO observations.

 (3) to study the variation of the IR colors on the edges of the
 cloud cores. The IRAS observations have shown that there exists
 a small transition region surrounding the core where the FIR
 colors dramatically change.