  We argue that the magnetic susceptibility data, Refs. 1-3, for the
low-density two-dimensional (2D) silicon-based electron gas indicate that
magnetically active electrons are localised in spin-droplets. The droplets
exist in both the insulating and metallic phases, and interact
ferromagnetically, forming an effective 2D Heisenberg ferromagnet. Comparing
the data with known analytical and numerical results for a 2D Heisenberg
ferromagnet, we determine that JS^2 \approx 0.6K, where S is the spin of the
droplet and J is the ferromagnetic exchange constant between droplets. We
further argue that most likely S=1 with four electrons occupying each droplet
on average. We discuss the dependence of the magnetic susceptibility and the
specific heat on the external magnetic field, which follows from the model, and
hence we suggest further experimental tests of the model.
