When such a coin is laid upon the red hot iron, the letters and figures become oxidated, and the film of oxide radiating more powerfully than the rest of the coin will be more luminous than the rest of the coin, and the illegible inscription may be now distinctly read to the great surprise of the observer, who had examined the blank surface of the coin previous to its being placed upon the hot iron.

The parts, however, where the letters of the inscription had existed, oxidate at a different rate from the surrounding parts, so that these letters exhibit their shape, and become legible in consequence of the film of oxide which covers them having a different thickness, and therefore reflecting a different tint from that of the adjacent parts.

I have found from numerous trials that it is always the raised parts of the coin, and in modern coins the elevated ledge round the inscription, that becomes first oxidated.

If we use an uniform and homogeneous disc of silver that has never been hammered or compressed, its surface will oxidate equally, provided all its parts are equally heated.

We do not assume that a something called "aquosity" entered into and took possession of the oxidated hydrogen as soon as it was formed, and then guided the aqueous particles to their places in the facets of the crystal, or amongst the leaflets of the hoar-frost.