Physical properties of colloidal solutions:
Heterogeneous character:
Colloidal particles being larger than molecules form heterogeneous mixture composed of particles of dispersed phase and dispersion medium. The phenomenon of Tyndall effect, electrophoresis and electro-osmosis confirm heterogeneity of colloidal systems.
Stability:
Colloidal sols are quite stable. Only a few colloidal particles of comparatively larger size may settle but very slowly.
Filtrability:
Ordinary filter paper cannot be used for removing the dispersed phase because size of pores of filter paper is bigger than the size of colloidal particles which can easily pass through the pores of the ordinary filter paper. Animal membrane or parchment paper does not allow the colloidal particles to pass through it. This forms the basis of separating the particles of the colloid from those of the crystalloids in the process called dialysis.
Visibility:
The particles in colloidal solution are not visible to naked eye or under ordinary microscope. In fact, a particle is not visible if its size is less than half the wavelength of the visible light used to see it. Since minimum wavelength of the visible light range is 3600 Å, therefore with visible light, a particle of size less than 1800 Å cannot be seen.
