(NaPO₃)_x Sodium phosphate groupings; cyclic forms range from x = 3 for the trimetaphosphate, to x = 10 for the decametaphosphate; sodium hexametaphosphate with x = 10 to 20 is probably a polymer; used for dental polishing, building detergents, and water softening, and as a sequestrant, emulsifier, and food additive.