Substance microscopically dispersed evenly throughout another substance. A colloidal system consists of two separate phases: a dispersed phase (or internal phase) and a continuous phase (or dispersion medium) in which the colloid is dispersed. A colloidal system may be solid, liquid, or gas. The dispersed-phase particles have a diameter of between approximately 1 and 1000 nanometers. Such particles are normally invisible in an optical microscope, though their presence can be confirmed with the use of an ultramicroscope or an electron microscope.