It is produced by the intervention of oxygen; for verdigris is a compound salt formed by the union of vinegar and copper; it is of a beautiful green colour, and much used in painting.
EMILY.
But, I believe, verdigris is often formed on copper when no vinegar has been in contact with it.
MRS. B.
Not real verdigris, but compound salts, somewhat resembling it, may be produced by the action of any acid on copper.
The solution of copper in nitric acid, if evaporated, affords a salt which produces an effect on tin that will surprise you, and I have prepared some from the solution we made before, that I might show it to you. I shall first sprinkle some water on this piece of tin-foil, and then some of the salt.—Now observe that I fold it up suddenly, and press it into one lump.
CAROLINE.
What a prodigious vapour issues from it—and sparks of fire I declare!
MRS. B.
I thought it would surprise you. The effect, however, I dare say you could account for, since it is merely the consequence of the oxygen of the salt rapidly entering into a closer combination with the tin.