If some gelatin is mixed in colloidal solution of gold, then it does

Gold sol is a lyophobic sol and unstable in nature.Addition of gelatin stabilises the gold sol because gelatin forms lyophilic sol and acts as a protective colloid. When a lyophilic sol is added to lyophobic sol,a layer of lyophilic sol is formed around each colloidal particle of lyophobic sol.This helps in stabilising the lyophobic colloid from the effect of electrolytes.Such lyophilic sols that are added to protect lyophobic sols are called protective  colloids.

Gelatine is a lyophilic sol while Gold sol is a lyophobic sol . When gelatine is added to gold sol it acts as a stabilising agent as it protects the gold sol by forming the layer of Gelatine particles around each Gold particle.Due to this the Gold particles cannot come in contact with Electrolytes.Due to this the charge on Gold colloid particles remains intact and they do not undergo coagulation.