Abundance variations in high-velocity interstellar gas

Based on line-of-sight models and profile-fitting, abundance variations of Ca, Si, Fe, and Na in high-velocity interstellar clouds toward ..mu.. Colombae, HD 28497, and HD 50896 are discussed. The correlation of larger rations N (Ca II)/N (Na I) with increasing radial velocity, in clouds with 20 km s/sup -1/< or =vertical-bar..nu..vertical-bar< or =100 km s/sup -1/, is shown to quite likely be due to abundance variations in Ca, rather than an ionization effect. Copernicus UV data show that the ratios N (Fe II)/N (S II) and N (Si II)/N (S II) have the same velocity correlation as Ca II, and the ambiguity concerning the relative adundance of Na I to hydrogen is removed. Theories of grain disruption are discussed as they relate to the observed Ca, Si, and Fe enhancements and their correlation with cloud velocity.