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  • A colloidal system in which both the dispersed phase as well as dispersion medium are immiscible or partially miscible liquids is called an emulsion. 
  • e.g. Milk, cod liver oil, oil paints, vanishing cream, cold creams, etc. 
  • Generally, one of the two liquids is water and the other which is immiscible with water is designated as oil. 
  • The liquid in excess is the dispersion medium and the liquid which forms droplets or globules is the dispersed phase.

Colloids have very important application in our daily life starting from food products to the medicines to industries like rubber. Some of the applications of colloids are mentioned below. 

Food and medicines:  Colloids have great application in food industries and food stuffs. Many of the food materials which we eat are of colloidal nature. Milk and also many milk products like chees, cream butter etc. are colloids. In more accurate way, milk is an emulsion (liquid in liquid colloidal system). In milk, butter and fat are dispersed in water. Bread is colloidal system in which air is dispersed in baked dough. Colloids also have applications in the form of medicines. Colloidal medicines are competitively more effective as they are easily absorbed by the body. That is way many medicines are emulsion. Some major antibiotics like penicillin and streptomycin are injected in the body in the form of colloidal sol so that they would be absorbed by the body easily. 

Water Purification: We know that one of the very popular methods used for water purification is the addition of electrolytes like potash alum. Addition of these electrolytes is based on the fact because the impure water in usually a colloidal system. It usually contains dispersed colloidal particles which cannot be removed by filtration. Addition of these electrolytes results in coagulation of the impurity which can be separated by filtration then. 

Sewage disposal: As discussed above the sewage water contains impurities like mud and dirt of colloidal size which are dispersed in the water. Just like any other colloidal system, the colloidal particles (impurities) of sewage are also charged particles.These charged particles of impurities present in sewage may be removed by electrophoresis. For this purpose the sewage water is passed through a tunnel which is fitted with metallic electrodes and is maintained at a high potential difference. 

The charged particles of impurity present in the sewage water migrate to the oppositely charged electrodes which results in their coagulation. 

Smoke precipitation:  Smoke is also a colloidal system which mainly consists of charged particles of carbon depressed in air

Smoke is a big problem for environment as it the major source for air pollution. Removal of the dispersed colloidal particles from the air will solve the problem. For this again the process of electrophoresis is used.

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The colloidal solution in which both the dispersed phase and dispersion medium are liquids is called an emulsion.

e.g. Milk, cod liver oil, oil paints, vanishing cream, cold creams, etc.

There are two types of emulsions:  

(a) Oil in water type:  Here, oil is the dispersed phase while water is the dispersion medium. For example: milk, vanishing cream, etc.     

(b) Water in oil type:  Here, water is the dispersed phase while oil is the dispersion medium. For example: cold cream, butter, etc.

Application of Colloids :

(1) Purification of water by alum (coagulation) 

(2) In rubber and tanning industry (coagulation and mutual coagulation) : Several industrial processes such as rubber plating, chrome tanning, dyeing, lubrication etc are of colloidal nature.

(3) Artificial rains : It is possible to cause artificial rain by throwing the electrified sand or silver iodide from an aeroplane and thus coagulating the mist hanging in air.  

(4) Smoke precipitation (Coagulation) : Smoke is a negative sol consisting of carbon particles dispersed in air. Thus, these particles are removed by passing through a chamber provided with highly positively charged metallic knob.  

(5) Formation of deltas (coagulation) : River water consists of negatively charged clay particles of colloidal dimension. When the river falls into the sea, the clay particles are coagulated by the positive  ions etc. present in sea water and new lands called deltas are formed.  

(6) Clot formation : Blood consists of negatively charged colloidal particles (albuminoid substance). The colloidal nature of blood explains why bleeding stops by applying a ferric chloride solution to the wound. Actually ferric chloride solution causes coagulation of blood to form a clot which stops further bleeding.  

(7) Colloidal medicine : Argyrol and protargyrol are colloidal solution of silver and are used as eye lotions colloidal sulphur is used as disinfectant colloidal gold, calcium and iron are used as tonics.  

(8) Coating of Photographic plates : These are thin glass plates coated with gelatin containing a fine suspension of silver bromide. The particles of silver bromide are colloidal in nature.

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