The word colloids is of Greek origin; the Greek word Kolla, meaning “glue”. Thomas Grahm is usually regarded as the Confider of Colloid Science. The subtance like glue, gelatin, starch etc. when added to water, form a solution which cannot pass through the animal membrane or semi-permeable membrane are called colloids. The resulting solution is called colloidal solution.
It is defined as a heterogeneous system consisting of two phases.
(1) A dispersed phase consisting of the colloidal particles and
(2) A dispersion medium in which the dispersion of the particles takes place and it forms the major portion of the solution. The particles of the colloidal solutions can pass through an ordinary filter paper but not through an animal membrane. It is obviously impossible to draw a boundary line between true solutions and colloidal solutions.
Examples: Dispersion of oil in water and dispersion of Arsenic sulphide in water forms colloidal solutions.