Charcoal is formed when carbon-containing compounds are heated in a limited supply of air.
Wood charcoal is obtained by the destructive distillation of dry wood in a hard glass test-tube.
The physical properties of wood charcoal are as follows:
1. It is black, porous and brittle.
2. It floats on water, because of its porosity. It also has an unpleasant smell.
3. Its specific gravity varies depending on the method of preparation. Usually it has a specific gravity of 1.5 to 1.9.
4. Wood charcoal is a bad conductor of heat and electricity.
Some chemical properties of wood charcoal are as follows:
1. When wood charcoal is heated in a free supply of oxygen, it burns at about 4000C and combines with oxygen to form carbon dioxide. In an insufficient supply of oxygen, it forms carbon monoxide.
2. It combines with sulphur vapour to form carbon disulphide.
3. It combines with hydrogen at high temperature to form mehane.
4. It reduces metal oxides to the corresponding metals. Oxides of calcium and silicon form their carbides on reacting with wood charcoal.
5. It reduces concentrated sulphuric acid and nitric acid, forming sulphur dioxide and nitrogen dioxide, respectively.
Some important uses of wood charcoal are as follows:
1. Wood charcoal is mainly carbon and thus, a better fuel than wood due to the following reasons.
a. Its calorific value is higher than that of wood.
b. Its ignition temperature is less than wood.
c. It causes less air pollution.
2. Wood charcoal is porous and can adsorb liquids and gases on its porous surface. Therefore, it is used in water filters, gas masks and antigastric tablets for people suffering from indigestion.
3. Charcoal is also used as a decolourizing agent as it can adsorb colouring matter. It is used for decourizing sugar solutions, organic preparations, alcohol and petroleum products.
4. Gun powder is a mixture of charcoal, potassium nitrate (KNO3) and sulphur.
Sugar charcoal and animal or bone charcoal. Sugar charcoal is prepared from cane sugar. It is the purest form of amorphous carbon. It is mainly used to manufacture artificial diamonds.
Bone charcoal is obtained by the destructive distillation of bones. It contains 10% carbon and 90% impurities like calcium phosphate and carbonate. Animal charcoal is also porous and can absorb coloring matter. It is used in the purification of organic liquids and as a decolorizing agent in the manufacture of sugar. It is also used in pain.