Mike's analysis is great for the ionic fraction of EIS but the colloidal fraction follows different physico- chemical principles. Dialysis membranes are probably the least expensive standard method to measure the sizes of nanocrystals. Semipermeable membranes of calibrated pore sizes cost less than $2 when bought in bulk. The membrane used by Thomas Graham in the 1860s remained in standard usage till the 1930s and beyond. It was so-called "vegetable parchment." Vegetable parchment is produced by reacting rag paper (celluose) with sulfuric acid and zinc choride, and thoroughly washing it. The result is a sheet with greater strength and much less permeability than ordinary paper.
Colloidal silver makers and testers probably should use the membrane techniques more often than is now done. Measuring colloidal properties without membranes is like staging Hamlet without the prince. Matthew
