The movement of electrically charged sol particles under the influence of an applied electric field is called electrophoresis. The velocity of the colloidal particles under a fall of potential one volt per cm is known as the electrophoretic mobility. It has been found that the range of 2 to 4×10-4 cm per sec. Electrophoresis consists of a U-tube fitted with a stopcock at the bottom for drainage. A colloidal solution like ferric hydroxide sol added into the tube. Now water (dispersion medium) is added on to the sot in both the limbs of U—tube. The electrodes are dipped in water one in each limb and connected to a high potential source. On applying the voltage the boundary between the sol and water begins to move towards the cathode. The level of water falls gradually on the side of the positive electrode and rises on the side of the negative electrode. On the other hand, if the sol particles are negatively charged, the level gradually falls on the side of the negative electrode and rises on the side of the positive electrode. Thus by noting the direction of movement of sol particles the nature of their charged can be known.