Conduction in multicomponent percolation

We present simulations and effective-medium theory calculations on conduction in a number of percolation models with up to four types of sites or bonds. We introduce the idea of chemical constraint in a multicomponent percolation system. The application of such models to the interpretation of recent experimental work on ${\mathrm{Na}}_x{\left(\mathrm{N}{\mathrm{H}}_3\right)}_{1-x}$ mixtures and on charge-transfer salts is discussed.