The use of gas for cooking and heating began in the middle of the 19th century with the introduction of gas stoves in 1840 and gas fires in 1855. The most important gaseous fuels are natural gas, coal gas and water gas. Nowadays, a certain amount of gas is made from oil. Today other processes have also been developed for the manufacture of a substitute or synthetic natural gas from coal.
Natural gas is obtained from the deposits of oil. This gas was once considered a hindrance during drilling of oil and was merely disposed off by burning at the oil fields. But now it is used as a fuel and feedstock. Natural gas and oil were formed from plants and animal remains at different depths inside the earth over million years of time. These are fossil fuels and were changed into gas or liquid at different temperatures by constant chemical processes beneath the earth. Natural gas is mainly composed of 85% methane, 10% ethane and the rest being propane, butane and nitrogen. It produces sufficient amount of heat on burning.
Coal gas is a mixture of gases that are given off when coal is converted into coke. The average composition of coal gas by volume is hydrogen 50%, methane 30% carbon monoxide 8%, oxygen, carbondioxide and nitrogen 8% and other hydrocarbon about 4%. This gas is produced by heating coal in the absence of air. Coal is heated in retorts or ovens to a temperature of approximately 1350°C so that it softens and releases its gas. This gas is thick and brown in colour because of the presence of coal-tar vapour and is used as an important fuel in homes and factories. Nowadays, however, it is being largely replaced by natural gas.
Water gas is a mixture of hydrogen and carbon monoxide. It is made by passing steam over red-hot coke. It is used in industries. It is bluish in colour. When water gas is mixed with coal gas, the mixture is known as town gas.
Oil gas is made by cracking the crude oil. Unlike other inflammable gases it does not contain many impurities and is thus of high quality. It contains mainly methane, acetylene and benzene. It is mixed with town gas and distributed in the normal way through a system of pipelines in advanced countries. This gas produces very small amounts of smoke and ash.