  Susceptibility and high field magnetization measurements have been performed
on powder samples of an $S$=1 bond alternating chain compound
[\{Ni(333-tet)($\mu$-N$_3$)\}$_n$](ClO$_4$)$_n$ (333-tet=tetraamine
N,N'-bis(3-aminopropyl)-1,3-propanediamine). As the temperature is decreased,
the susceptibility exhibits a round maximum at around 120 K and decreases
gradually down to 10 K, and then falls down rapidly with a logarithmic
curvature which is behavior of the susceptibility of a gapless or a nearly
gapless antiferromagnetic chain. Magnetization up to 50 T at 1.4 K shows no or
a very small gap in this compound. We have carried out numerical calculations
for the $S$=1 antiferromagnetic bond alternating chain with various alternating
ratios $\alpha$ and obtained a very good agreement between experiments and
calculations for $\alpha$=0.6. We verify experimentally that the gapless point
exists around $\alpha$=0.6.
