Fasten a sprig of fresh rosemary, or any similar shrub, to the inside
of a small bandbox, near the top; heat a thick tile, and sprinkle it
with gum benzoic, and immediately place the bandbox over it, when the
acid will be sublimed by the heat, and will condense in a white vapour
upon the green plant, giving it the appearance of being covered with
hoarfrost.