Glass 

Glass is hard, transparent, amorphous metallic silicate of different metals. Glass, though seems to be solid, the molecules of glass are found moving very slowly like that occurs in extremely cold liquid so it is also called a super cooled liquid. That is why the window pane of old houses got thick at the bottom while thin at the top. The main raw material or component of glass is silica found in sand. 

Depending upon the components and chemical mixed in it, glass is of different types. Some of them are given below. 

1. Quartz glass:

When pure silica is strongly heated at 1600°C and allowed to cool slowly, it turns into quartz glass.

Pure silica when heated on 1600C becomes, Quartz glass .

It differs from other glasses in not containing any other ingredients except silica. Therefore, it is superior to other types of glasses due to its purity. For these reasons, it is used to make laboratory equipment, lenses, gems, basins, crucibles, electric tools, etc. 

2. Water glass

When a mixture of silica (SiO2) and sodium carbonate (Na2CO3) or potassium carbonate (K2CO3) is heated at 800°C water glass is formed which is sodium silicate.

SiO2 + Na2CO3  ---􀀉•• Na2SiO3 + CO2 

                                Sodium silicate 

K2SiO3 + CO2

                                    Potassium silicate

It is soluble in water, so it is called water glass. Water glass is used for making fireproof materials, adhesive and chemical garden. A chemical garden is an experiment in chemistry normally performed by adding metal salts such as copper sulphate or cobalt (II) chloride to an aqueous solution of water glass. This results in growth of plant like forms in minutes to hours. 

3. Ordinary glass or soda glass

The glass formed by fusing a mixture of 50% silica, 15% sodium carbonate, 10%calcium carbonate and 25% glass pieces at 850°C in a special type of tank furnace is ordinary or soda glass. It is the most common type of glass. The mixture melts into a viscous liquid, which is poured into moulds or blown with iron pipe to make different glasswares. The almost ready glasswares are cooled slowly. This process is known as annealing. Annealing makes the glassware resistant to temperature fluctuation. By this process, glasswares do not break easily when something hot or cold is put in it.

2SiO2 + Na2CO3 + CaCO3 ----Na2SiO3.CaSiO3 + 2CO2

Glass pieces

Ordinary glass is used for making bottles, light bulbs, window panes and several other useful objects. It is also known as soft glass.

4. Hard glass or potash lime glass

The glass formed by fusing a mixture of potassium carbonate, calcium carbonate and silica is called hard glass or potash lime glass. It has high melting point and can withstand high temperature.

It is used for making laboratory apparatus like beakers, hard glass test tube, tube lights etc.

5. Borosilicate glass

The glass formed by fusing a mixture of silica, sodium carbonate, calcium carbonate and boric oxide is called borosilicate glass or pyrex glass. It is resistant to the chemicals and heat.

5SiO2 + Na2CO3 + CaCO3 + B2O3 􀀟 • Na2SiO3.CaSiO3 B2 (SiO3)3 + 2CO2

It is used to make laboratory apparatus such as test tubes, breakers, flasks, condensers and kitchenwares. 6.

6.Lead crystal glass

The glass made by fusing a mixture of silica, potassium carbonate and lead monoxide is called lead crystal glass. This type of glass has high refractive index.

 2Si02 + K2C03 + PbO on heating gives K2Si03.PbSi03 + CO2 

It is used to make apparatus like hard glass test tube, prism, lenses, high quality and kitchenwares.

7.Coloured glass 

The glass is made coloured by adding different metal oxide in molten glass. Different metallic oxides impart different colours.

Coloured glass is used for making sunglasses, decorative items, signals for automobiles, trains and aeroplanes, etc. 

Some examples are given below.