Source of heat in industries
Explanation
Coal gas is a gaseous byproduct obtained during the destructive distillation of coal. This process involves heating coal in the absence of air to produce coke, coal tar, and coal gas.
Detailed Analysis:
- Manufacturing of steel is incorrect: The manufacturing of steel primarily utilizes Coke. Coke is a tough, porous, and black substance that is an almost pure form of carbon. It acts as a reducing agent in the extraction of metals and steel production.
- Source of heat in industries is correct: Coal gas is a mixture of hydrogen, methane, and carbon monoxide. It has a high calorific value and is combustible. Therefore, its primary application is as a fuel to provide a source of heat for industries, particularly those situated near coal processing plants. Historically, it was used for street lighting before being replaced by electricity.
- Metalling of roads is incorrect: The metalling of roads was traditionally done using Coal Tar, a thick black liquid with an unpleasant smell. In modern applications, bitumen (a petroleum product) has largely replaced coal tar for road surfacing.
- Lubrication of machinery is incorrect: Lubrication of machinery typically involves lubricating oils, which are fractions obtained from the refining of petroleum, not from coal gas.
Key Takeaway:
Coal gas is used as an industrial fuel (source of heat), whereas Coke is used in metallurgy (steel manufacturing), and Coal tar is used for synthesizing various industrial chemicals (dyes, drugs, explosives).