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With this proposal we aim to investigate the relation between dust grain evolution comma dust composition comma dust extinction properties and environment in the Milky Way. To enable this comma we need to expand the sample of depletion measurements comma in particular to increase the number of sightlines with C and Si measurements comma the two principal components of dust grains. We propose STIS spectroscopic observations towards 17 stars in a total of 31 orbits. These data (in combination with the available archival data) will allow us to study dust properties in a wide range of environments (from dense to diffuse gas clouds) comma and help us understand which mechanisms play a role in dust evolution in the Milky Way.