Column density relation between our observed o-NH₃ and N₂H⁺ and CS respectively. The column densities are calculated from optical depths integrated over five velocity bins associated with absorption features as indicated by capital letters in the plot. N₂H⁺ and CS data as well as ranges of velocity bins are adopted from Greaves & Nyman (1996). The solid lines show the logarithmic least-square fits to each of the data sets, and their slopes are 1.15 ± 0.27 and 0.63 ± 0.07 for CS and N₂H⁺, respectively.