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Sympathetic Inks

 Table of Substances Used in Making Sympathetic Inks: -

For writing and for bringing out the writing:

Cobalt chloride, heat.
Cobalt acetate and a little saltpeter, heat.
Cobalt chloride and nickel chloride mixed heat.
Nitric acid, heat.
Sodium chloride, heat.
Saltpeter, heat.
Copper sulphate and ammonium chloride, heat.
Silver nitrate, sunlight.
Gold trichloride, sunlight.
Ferric sulphate, infusion of gallnuts or Ferro cyanide of potassium.
Copper sulphate, Ferro cyanide of potassium.
Lead vinegar, hydrogen sulphide.
Starch water, tincture of iodine or iodine vapors.
Cobalt nitrate, oxalic acid.
Fowler’s solution, copper nitrate.
Soda lye or sodium carbonate, phenolphthaleine.

A sympathetic ink is one that is invisible when written, but which can be made visible by some treatment. Common milk can be used for writing, and exposure to strong heat will scorch and render the dried milk characters visible.

The following inks are developed by exposure to the action of reagents:

1. – Upon writing with a very clear solution of starch on paper that contains but little sizing, and submitting the dry characters to the vapor of iodine (or passing over them a weak solution of potassium iodide), the writhing becomes blue, and disappears under the action of a solution of hyposulphite of soda (1 in 1,000).

2. – Characters written with a weak solution of the soluble chloride of platinum or iridium become black when the paper is submitted to mercurial vapor. This ink may be used for marking linen, as it is indelible.