OXYGEN AND NITROGEN.

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gass or permanently elastic fluid, a chemical com-bination must take place between the caloric andthe substance, at the time of its being convertedinto a gaseous state; it is necessary, therefore,that there should be an affinity between them,and hence their combination cannot be destroyedby a mere change of temperature, or by any che-mical agents, except such as have a stronger affi-nity, for either of the constituents of the gas, andby that means effect its decomposition.

CAROLINE.

Indeed, I ought not to have forgotten that ca-loric, in vapour, is only latent, and not chemicallycombined. But pray, Mrs. B., what kinds ofsubstances are oxygen and nitrogen, when not ina gaseous state ?

MRS. B.

They have never been obtained in their puresimple state, because they cannot be separatedentirely either from caloric or from the otherbodies with which they are found united; it istherefore only by their effects in combining withother substances that we are acquainted withthem.

CAROLINE.

How much more satisfactory it would be if wecould see them!