Having derived estimates of the densities and radiation fields within several interstellar clouds from the observed populations of the H$sub 2$ rotational levels, we can estimate the amount of sodium and calcium depletion within different clouds. If the H$sub 2$ formation rate R equals 3times10$sup - 17$ cm$sup 3$ s$sup -1$, and if the hydrogen ionization rate is less than 10$sup - 16$ s$sup -1$, we find that in most clouds with E (B-V) less than or equal to0.10, sodium is at most slightly depleted, while calcium is always substantially depleted. This result is important for determining the thermal equilibrium within diffuse interstellar clouds. (AIP)