  We analyze the logarithmic corrections due to ferromagnetic impurity ending
bonds of open spin 1/2 antiferromagnetic chains, using the density matrix
renormalization group technique. A universal finite size scaling $\sim {\frac 1
{L \log L}}$ for impurity contributions in the quasi-degenerate ground state
energy is demonstrated for a zigzag spin 1/2 chain at the critical next nearest
neighbor coupling and the standard Heisenberg spin 1/2 chain, in the long chain
limit. Using an exact solution for the latter case it is argued that one can
extract the impurity contributions to the entropy and specific heat from the
scaling analysis. It is also shown that a pure spin 3/2 open Heisenberg chain
belongs to the same universality class.
