Sols are lyophobic (solvent-hating) suspensions of solid particles (1-1000 nanometres in size) in a liquid. Sols may be prepared by dispersion or condensation. Dispersion techniques include grinding solids to colloidal dimensions in a ball mill (dry or wet) and Beidig's arc method. Condensation or precipitation methods work by making the colloidal particle come out of solution into the colloidal phase, either by adding a precipitating agent (salt) or by changing the temperature. The stability of sols may be maintained by using dispersing agents. Sols may be a component of total dissolved solids, since the particle size is small enough to pass through a two micrometre filter. Sols are commonly used in preparing sol gels. example: Blood, Pigmented Inks and Milk
