  We have studied the magnetic field dependence of the ground state energies in
a small Si quantum dot. At low fields the first five electrons are added in a
spin-up -- spin-down sequence minimizing the total spin. This sequence does not
hold for larger number of electrons in the dot. At high fields the dot
undergoes transitions between states with different spins driven entirely by
Zeeman energy. We identify some features that can be attributed to transitions
between different spin configurations preserving the total spin of the dot. For
a few peaks we observed large linear shifts that correspond to the change of
the spin of the dot by 3/2. Such a change requires that an electron in the dot
flips its spin during every tunneling event.
