MRS. B.
They all do, more or less, excepting gold, silver, and platina.
Copper, lead, and iron, oxydate slowly in the air, and cover themselves with a sort of rust, a process which depends on the gradual conversion of the surface into an oxyd. This rusty surface preserves the interior metal from oxydation, as it prevents the air from coming in contact with it. Strictly speaking, however, the word rust applies only to the oxyd, which forms on the surface of iron, when exposed to air and moisture, which oxyd appears to be united with a small portion of carbonic acid.
EMILY.
When metals oxydate from the atmosphere without an elevation of temperature, some light and heat, I suppose, must be disengaged, though not in sufficient quantities to be sensible.
MRS. B.
Undoubtedly; and, indeed, it is not surprising that in this case the light and heat should not be sensible, when you consider how extremely slow, and, indeed, how imperfectly, most metals oxydate by mere exposure to the atmosphere. For the quantity of oxygen with which metals are capable of combining, generally depends upon their temperature; and the absorption stops at various points of oxydation, according to the degree to which their temperature is raised.
EMILY.
That seems very natural; for the greater the quantity of caloric introduced into a metal, the more will its positive electricity be exalted, and consequently the stronger will be its affinity for oxygen.
MRS. B.