The Bureau of Mines measured the vapor pressure of fecl2, febr2, fei2, sb, bi, cd, mg, pb, fecl3, and vcl2 using the knudson- and torsion-effusion methods, and on fecl3-nacl mixtures, au2cl6, and mgni2 using only the knudsen method. Apparent vapor pressures calculated from the experimental data vary with orifice size and method of determination. Reaction with residual oxygen in the instruments was noted to have an effect on the iron halide data. Vapor pressure curves plotted as log p versus 1/t (where p is pressure and t is absolute temperature) for one substance using several orifice sizes tended to converge at a single point when extrapolated beyond the experimental region. All of the data, except those of vcl2, agree with previously published results. The importance of comparing effusion measurements with those obtained by other methods and the variations encountered with various orifice sizes are discussed.