Interstellar Silicon Abundance

We present 34 measurements of silicon gas phase column densities in the interstellar medium. We have used spectra containing the Si II 1808 Å line which were obtained with the Goddard High Resolution Spectrograph (GHRS) aboard the Hubble Space Telescope (HST). Extinction curve parameters are determined for analyzed lines of sight and relation between Si/H ratio and extinction parameters is discussed. We find the abundance of gas phase silicon in diffuse clouds to be lower than the solar value by a factor of four.