Proteins form a colloidal solution, and their solubility is dependent o charges and shell of hydration around them. From solutions, proteins are precipitated by disturbing charge properties and shell of hydration, and by denaturation. Salts, concentrated acids, alkaloidal reagents, heavy metals, alcohol are the chemical agents used to precipitate proteins while heating is the physical force used. Precipitation reactions are useful in detection and estimation of proteins in body fluids such as urine and CSF; in deproteinization of samples in clinical chemistry assays; and in fractionation of plasma proteins.