Coal gas is a flammable gas produced by heating coal in the absence of air, a process known as carbonization. It primarily consists of hydrogen, methane, carbon monoxide, and other gases. Historically, coal gas was used for lighting, heating, and cooking before the widespread adoption of natural gas. The production of coal gas began in the 19th century and played a significant role in the industrial revolution. However, its use declined with the rise of cleaner and more efficient energy sources, such as natural gas and electricity. Today, coal gas is less common but can still be produced for specific industrial applications.