Double electric layer is made from potential determining ions that are tightly bound by the solid surface, and the equivalent amount of oppositely charged ions (counter ions).{mAgI?nI-?(n - x)K+}-x?xK+
{aggregate?PDI?counter ions from adsorption layer}?diffuse layer
{nucleus?counter ions from adsorption layer}?diffuse layer
{granule}?diffuse layer
            In this scheme "m" shows the number of units of AgI in the aggregate; "n" shows the number of potential determining ions; "x" shows the number of counter ions in the diffusion layer. The charge of a granule in this scheme is equal to "-x".As an example we can take a sol formed after the reaction between water solutions of two salts: the excess of potassium iodide (KI) and relatively low amount of silver nitrate (AgNO3).The layer of counter ions is divided into two parts: the first layer is called adsorption layer and it is made from oppositely charged ions interacting with ions from potential determining layer; the second layer is called diffusion layer since those ions are not directly adsorbed on a surface.Aggregate and the layer of potential determining ions form a nucleus of colloid particle.KI + AgNO3 -> KNO3 + AgI?.