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Invisible Ink

Put litharge of lead into very strong vinegar, and let it stand

twenty-four hours. Strain it off, and let it remain till quite

settled; then put the liquor in a bottle.

You next dissolve orpiment in quick lime water, by setting the water

in the sun for two or three days, turning it five or six times a-day.

Keep the bottle containing this liquor well corked, as the vapour is

highly pernicious if received into the mouth.

Write what you wish with a pen dipped in the first liquor; and, to

make it visible, expose it to the vapour of the second liquor. If you

wish them to disappear again, draw a sponge or pencil, dipped in aqua

fortis, or spirit of nitre, over the paper; and if you wish them to

re-appear, let the paper be quite dry, and then pass the solution of

orpiment over it.