Matter & Energy

Matter is composed of atoms or groups of atoms called molecules. The arrangement of particles in a material depends on the physical state of the substance. In a solid, particles form a compact structure that resists flow. Particles in a liquid have more energy than those in a solid. They can flow past one another, but they remain close. Particles in a gas have the most energy. They move rapidly and are separated from one another by relatively large distances.

Fuel Gases

Fuel Gases, any combustible gaseous mixture used as fuel to provide energy for domestic or industrial use (see Combustion; Fuel).

Fuel gases consist principally of hydrocarbons, that is, of molecular compounds of carbon and hydrogen. The properties of the various gases depend on the number and arrangement of the carbon and hydrogen atoms within their molecules. All these gases are odorless in the pure state, and carbon monoxide is toxic. It is therefore common practice to add sulfur compounds to manufactured gas; such sulfur compounds, which are sometimes normally present in the gas, have an unpleasant smell and serve to give warning of a leak in the supply lines or gas appliance. In addition to their combustible components most gases have varying amounts of noncombustible nitrogen and water as their end products.

The devices used to burn gas for either heat or illumination consist of a burner nozzle and some means of mixing air with the gas before it reaches the nozzle, as, for example, in the Bunsen burner invented by British chemist and physicist Michael Faraday and improved and popularized by German chemist Robert Wilhelm Bunsen. See Lamp.

Fuel gases still in use are coal gas, made by the destructive distillation of coal (see Coal; Coke); producer gas and blast-furnace gas, made by the interaction of steam, air, and carbon; natural gas, drawn from gas deposits in the earth; and bottled gases, made from the lighter hydrocarbons.


The most important coal-gasification processes aim chiefly at production of so-called pipeline quality gas, which is reasonably interchangeable with natural gas. Gas from coal, besides having pumping and heating specifications, must meet strict limits on content of carbon monoxide, sulfur, inert gases, and water. To meet these standards, most coal-gasification processes culminate with gas cleanup and methanation operations. Various hydrogasification processes, in which hydrogen reacts directly with coal to form methane, are used today; these processes bypass the indirect step of producing synthesis gas, hydrogen and carbon monoxide, before an upgrading yields methane. Other coal-gas processes include the carbon dioxide acceptor process, employing the lime-bearing material dolomite, and the molten salt process. These processes work indirectly to produce synthesis gas first. Other gases manufactured formerly from coal and coke, such as illumination gas and coke-oven gas, are of little or no importance today.


A certain amount of natural gas almost always occurs in connection with oil deposits and is brought to the surface together with the oil when a well is drilled. Such gas is called casing-head gas. Certain wells, however, yield only natural gas.

Natural gas contains valuable organic elements that are important raw materials of the natural-gasoline and chemical industries. Before natural gas is used as fuel, hydrocarbons such as butane, propane, and natural gasoline are extracted as liquids. The remaining gas constitutes so-called dry gas, which is piped to domestic and industrial consumers for use as fuels; dry gas, devoid of butane and propane, also occurs in nature. Composed of the lighter hydrocarbons methane and ethane, dry gas is used also in the manufacture of plastics, drugs, and dyes.


Several of the lighter hydrocarbons, such as propane, butane, pentane, and mixtures of these gases are liquefied and employed as fuels. These so-called bottled gases, which are usually stored in steel cylinders, make possible the use of appliances such as cooking stoves and heaters in localities where a centralized gas supply is not available. Such bottled gases are produced from natural gas and petroleum.

See also Synthetic Fuels; Petroleum.