Relativistic heavy ion collisions are studied assuming that particles can be
described by a hadron gas in thermal and chemical equilibrium. The exact
conservation of baryon number, strangeness and charge are explicitly taken into
account. For heavy ions the effect arising from the neutron surplus becomes
important and leads to a substantial increase in e.g. the π−/π+ ratio.
A method is developed which is very well suited for the study of small systems.Comment: 5 pages, 5 Postscript figure