Minimum quantity of an electrolyte required to cause precipitation of a sol is called its coagulating value. Greater the charge on flocculating ion and smaller is the amount of electrolyte required for precipitation, higher is the coagulating power of coagulating ion (Hardy-Schulze Law).

Phosphate ion bear - 3 charge while chloride ion carries only -1 charge and due to high charge phosphate ion has high coagulating power than that of chloride ion.

Blood is a colloidal sol. When we rub the injured part with moist alum then coagulation of blood takes place. Hence, main reason is coagulation, which stops the bleeding.

Charge on sol is decided by adsorption of ions present in medium. Adsorption of positively charged $\mathrm{Fe}^{3+}$ ions takes place by the sol of hydrated ferric oxide. Thus, $\mathrm{Fe}(\mathrm{OH})_3$ colloid has positive charge when prepared by adding $\mathrm{Fe}(\mathrm{OH})_3$ to hot water.

Behaviour of physisorption and chemisorption on increase in temperature can be explained on the basis of nature of forces present to bind their particles. Physisorption involves weak van der Waals' forces which weakens with increase in temperature. Chemisorption involves formation of chemical bond which requires activation energy hence, it is favoured by rise in temperature.

Traces of electrolyte which stabilises the colloids is removed completely making the colloid unstable. So, coagulation occurs on prolonged dialysis.