OXYGEN AND NITRQGEN.

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MRS. B.

In a general point of view, it may be said toconsist of all tlie substances capable of existing,in an. aeriform state, at the common temperatureof our globe. But, laying aside these heteroge-neous and accidental substances (which ratherfloat in the atmosphere than form any of its com-ponent parts), it consists of an elastic fluid calledatmospherical air, which is composed of twogasses, known by the names of oxygen gasand nitrogen or azotic gas.

EMILY.

Pray what is a gas ?

MRS. B.

The name of gas is given to any aeriform fluid),which consists of some substance chemically com-bined with caloric, and capable of existing con-stantly in an aeriform state, under the pressure,and at the temperature of the atmosphere. Everyindividual gas is therefore composed of two parts :first, the particular substance that is converted intoa gas, by caloric; that is called the basis of thegas, as it is from it that the gas derives all its spe-cific and characteristic properties: and, 2dly, thecaloric, which, by its chemical combination withthe basis, constitutes it a gas, or permanentlyelastic fluid.

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