How stable is the hydrophilic colloid?

It mainly depends on its strong solvation and hydration layer of colloidal particles. Because the hydration layer around the colloidal particles hinders the mutual coalescence of particles, the thicker the hydration layer, the greater the stability. Therefore, any factor that can destroy the hydration layer of colloidal particles can cause the instability of hydrophilic colloid. If a small amount of electrolyte is added to the hydrophilic colloid, it will not cause condensation due to the ion action of opposite charge. Once the hydration layer is removed and hydrophobic colloidal particles are formed, it is easy to precipitate on the condensation surface. For example, after ethanol is added to gum arabic, agar and other colloidal solutions for dehydration, the colloidal particles lose their hydration layer and coagulate when they meet cations. Similarly, if a large amount of electrolyte is added to the hydrophilic colloid, due to the strong hydration property of the electrolyte ion itself, after addition, the hydration layer of the colloidal particles will be removed, which will also cause condensation and precipitation. This action is called salting out.

Adding a large amount of dehydrating agents such as ethanol, acetone and syrup into the hydrophilic colloid can also destroy the solvated colloidal particle hydration layer, dehydrate and precipitate. Or, although it is not precipitated, it is more susceptible to salt out due to its increased sensitivity to electrolyte.

If the hydrocolloid undergoes chemical changes due to the influence of light, heat, air, etc., and its change product has a small solubility, condensation will also occur. If incoherent liquid is added to the colloidal solution and then powered on, or violently shaken, or boiled or frozen, some or all of the colloidal particles can be condensed. Ultraviolet ray and X-ray can also make the glue sensitive to electrolyte.