We consider finite closed Jackson networks with N first come,
first serve nodes and M customers. In the limit $M \to \infty, N \to
\infty, M/N \to \lambda > 0$, we get conditions when mean queue lengths are
uniformly bounded and when there exists a node where the mean queue length
tends to $\infty$ under the above limit (condensation phenomena, traffic jams),
in terms of the limit distribution of the relative utilizations of the nodes.
In the same terms, we also derive asymptotics of the partition function and of
correlation functions.