Give reasons for the following :
(i) Peptazing agent is added to convert a precipitate into a colloidal solution.
(ii) Colloidal gold is used for intramuscular injection.
(iii) Cottrell's smoke precipitator is fitted at the mouth of a chimeny used in factories.

Explanation

(i) A precipitate adsorbs certain ions (positive or negative) from the electrolyte depending upon is nature and gets charged. These charged ions reple one another and change to colloidal size particles. For example ferric chloride `(FeCl_(3))` acts as a pertising agent for ferric hydroxide precipitate
`underset("Precipitate")(Fe(OH)_(3))+underset("Peptising agent")(Fe^(3+))to underset("Colloidal sol")([Fe(OH)_(3)]Fe^(3+))`
(ii) Particles of gold whihc are in colloidal form, gel easily adsorbed or assimilated by the particles of blood whihc are also of colloidal nature.
(iii) Cottell's smoke precipiate consists of charged plates which have charge opposite to the charge carried by the smoke particles. When these particles come in contact with these charged plates, they get their charge neutralised. In the absence of any charge, they get coagulated or precipitated as solid particles. The smoks coming out chimney is the free from these particles which are likely to polluted the atmosphere.