Kb = RTb^2M_solvent/(1000delta_H_vap). Kf = RTf^2M_solvent/(1000delta_H_fus). These depend ONLY on the solvent. Higher Tb (or Tf) and lower delta_H_vap (or delta_H_fus) give larger constants. For water: Kb = 0.512 (small because delta_H_vap is large). Kf = 1.86 (larger because delta_H_fus is smaller). Camphor has Kf = 40 — extremely high because its delta_H_fus is low and Tf and M_solvent are favorable. This makes camphor the best solvent for Rast's method of molar mass determination by freezing point depression. Higher K means larger measured delta_T for the same molality, giving more precise results.