ISEE 1 and ISEE 3 three-dimensional solar wind plasma measurements are used together with magnetic field measurements across five previously studied interplanetary shocks to test the accuracy of the mixed-mode shock-normal determination technique and to test whether the shock properties are best approximated with a ratio of specific heats of 5/3 or 2. In the shocks examined, the assumption that the velocity jump was along the normal provided an estimate of the shock normal within 15¿ of our best fit normal 50% of the time and within 50¿, 90% of the time. The mixed-mode normals lay within 12¿ of our best fit normal 50% of the time and within 36¿, 90% of the time. Part of this deviation may be due to differnces in the orientation of the local normal from that of the average normal. Finally, the jump in plasma and field across the shock is better predicted from the Rankine-Hugoniot equations using a ratio of specific heats (4) of 5/3 rather than 2.