APPLICATIONS OF COLLOIDS
Most of the substances, we come across in our daily life, are colloids. The meal we eat, the clothes we wear, the wooden furniture we use, the houses we live in, the newspapers we read, are largely composed of colloids.
The applications of colloid chemistry are limitless. These can be divided mainly into two classes:
i. Natural applications and
ii. Technical applications
I. Natural applications
(i) Blue colour of the sky : Colloidal particles scatter blue light. Dust particles along with water suspended in air scatter blue light which reaches our eyes and the sky looks blue to us.
(ii) Fog, mist and rain : When a large mass of air, containing dust particles, is cooled below its dewpoint, the moisture from the air condenses on the surfaces of these particles forming fine droplets. These droplets being colloidal in nature continue to float in the air in the form of mist or fog.
Clouds are aerosols having small droplets of water suspended in air. On account of condensation in the upper atmosphere, the colloidal droplets of water grow bigger and bigger in size, till they come down in the form of rain. Sometimes, the rainfall occurs when two oppositively charged clouds meet.
It is possible to cause artificial rain by throwing electrified sand or spraying a sol carrying charge opposite to the one on clouds from an aeroplane.
(iii) Food articles : Milk, butter, halwa, ice creams, fruit juices, etc., are all colloids in one form or the other.
(iv) Blood : Blood is a colloidal solution of an albuminoid substance. The styptic action of alum and ferric chloride solution is due to coagulation of blood forming a clot which stops further bleeding.
(v)Soils : Fertile soils are colloidal in nature in which humus acts as a protective colloid. On account of colloidal nature, soils adsorb moisture and nourishing materials.
(vi) Formation of delta : River water is colloidal solution of clay. Sea water contains a number of electrolytes. When river water meets the sea water, the electrolytes present in sea water coagulate the colloidal solution of clay which get deposited with the formation of delta.
Electrical precipitation of smoke : Smoke is a colloidal solution of solid particles such as carbon, arsenic compounds, dust, etc., in air. The smoke, before it comes out from the chimney, is led through a chamber containing plates having a charge opposite to that carried by smoke particles. The particles on coming in contact with these plates lose their charge and get precipitated. The particles thus settle down on the floor of the chamber. The precipitator is called Cottrell precipitator.
Purification of drinking water : The water obtained from natural sources often contains bacteria and suspended impurities. Alum is added to such water so as to destroy the bacteria as well as to coagulate the suspended impurities and make water fit for drinking purposes.
Medicines : Most of the medicines in use are colloidal in nature. For example, argyrol is a silver sol used as an eye lotion. Colloidal antimony is used in curing kalazar. Colloidal gold is used for intramuscular injection. Milk of magnesia, an emulsion, is used for stomach disorders. Colloidal medicines are more effective because these are easily assimilated.
Tanning : Animal hides are colloidal in nature. When a hide, which has positively charged particles, is soaked in tannin, which contains negatively
charged colloidal particles, mutual coagulation takes place, which results in the hardening of leather. The process is termed as tanning. Chromium salts have been used in place of tannin.
(v) Photographic plates and films : The photographic plates or films are prepared by coating an emulsion of the light sensitive silver bromide in gelatin over glass plates or celluloid films.
Rubber industry : Latex is a colloidal solution of rubber particles which are negatively charged. Rubber is obtained by coagulation of latex.
Industrial products : Paints, inks, synthetic plastics, rubber, graphite lubricants, cement, etc., are all colloidal solutions..