Top panel: R_V values and the corresponding E(B − V)/N_H ratios in units of 1.7 × 10^-22 mag cm², as derived from our WD dust grain models (see text); symbols are as in the previous figures; the dashed line connects the results of WD models of normal curves corresponding to seven different R_V values (Sect. 3); the range in bold-face on the x-axis shows the expected deviation of Galactic curves (Bohlin et al. 1978). Bottom panel: behavior of the reddening E(B − V) (Savage et al. 1985) as a function of the predicted total hydrogen column density; continuous line shows the average Galactic relationship found by analyzing a large sample of sight lines whose HI and H₂ column densities were measured: E(B − V)/N(H) = 1.7 × 10^-22 mag cm² (Bohlin et al. 1978); symbols are the same as in the previous figures.