When freshly precipitated $\mathrm{Fe}(\mathrm{OH}{)}_3$ is boiled with water in the presence of few drops of dil HCl, a hydrated ferric oxide sol is obtained. This method is termed 

On treatment of freshly prepared ferric hydroxide with small amount of ferric chloride in presence of dil hydrochloric acid solution forms a dark reddish brown solution. In this reaction, ferric chloride acts as a peptizing agent and the process is known as peptization.