gas

Origin: Invented by the chemist Van Helmont of Brussels, who died in 1644.

1. An aeriform fluid; a term used at first by chemists as synonymous with air, but since restricted to fluids supposed to be permanently elastic, as oxygen, hydrogen, etc, in distinction from vapors, as steam, which become liquid on a reduction of temperature. In present usage, since all of the supposed permanent gases have been liquified by cold and pressure, the term has resumed nearly its original signification, and is applied to any substance in the elastic or aeriform state.

2. A complex mixture of gases, of which the most important constituents are marsh gas, olefiant gas, and hydrogen, artificially produced by the destructive distillation of gas coal, or sometimes of peat, wood, oil, resin, etc. It gives a brilliant light when burned, and is the common gas used for illuminating purposes. Laughing gas.

Any irrespirable aeriform fluid.

Gas is often used adjectively or in combination; as, gas fitter or gasfitter; gas meter or gas-meter, etc.

<chemistry> Air gas, a kind of gas made by forcing air through some volatile hydrocarbon, as the lighter petroleums. The air is so saturated with combustible vapor as to be a convenient illuminating and heating agent.

<physics> Gas battery, a kind of gas made by forcing steam over glowing coals, whereby there results a mixture of hydrogen and carbon monoxide. This gives a gas of intense heating power, but destitute of light-giving properties, and which is charged by passing through some volatile hydrocarbon, as gasoline.

Source: Websters Dictionary