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Light and Its Phenomena: Gases

Vegetables are compounded of oxygen, hydrogen, carbon, and some nitrogen; animals of oxygen, nitrogen, hydrogen, carbon, phosphorus, and lime. A man generates nearly a cubic food of carbonic acid per hour, by which he gives off half an ounce of carbon, and the conversion of oxygen gives out the precise quantity of animal heat, in the difference of the specific heat of both. Gases mix equally, and when mixed do not separate. This is ascribed to the particles being of different sizes. Gases of different gravities become uniformly diffused by mutual absorption. Hence hydrogen is not generally uppermost in the atmosphere, nor carbonic acid undermost.

Carbonic acid gas is a product of fermentation, and being heavier than air it lies all over fermentive processes, puts out a candle, and produces suffocation. At the bottom of wells and coal mines it causes the choke damp, in which a light will not burn, but which may be dispersed by throwing water into it. Water constantly absorbs it in the ratio of pressure, and parts with it when the pressure is removed, called "effervescence" in bottled liquors.