The double focusing mass spectrometer previously described has been used to measure 27 atomic masses in the region from titanium to zinc. When supplemented by our earlier values and nuclear reaction energies the data give the masses of 81 nuclides between mass numbers 31 and 70. A fit of the semi-empirical mass formula of Wigner indicates the existence of magic numbers at 20 and 28 protons and neutrons associated with discontinuities in the binding energy surface. The discontinuities are primarily changes in slope of the surface.

• Received 21 January 1951

DOI:https://doi.org/10.1103/PhysRev.86.408