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Sympathetic Inks (Such as do not appear after)

Sympathetic inks are such as do not appear after they are written with, but which may be made to appear at pleasure by certain means to be used for that purpose. A variety of substances have been used as sympathetic inks, among which are the following:

Chloride of Gold and Tin.

Write with a solution of gold in aqua regia, and let the paper dry gently in the shade. Nothing will appear, but draw a sponge over it, wetted with a solution of tin in aqua regia, and the writing will immediately appear, of a purple color. Starch and Iodine.

Write with weak boiled starch, and when the writing is required to appear, brush over with a weak solution of iodine; the letters will appear blue.

Chloride of Cobalt, When pure, is invisible in dilute solution, but gives a blue when exposed to a gentle heat; if it contain (as it usually does) some nickel, the color will be green. A little common salt should be added to the solution, so that it will remain more on the paper. It can then be brought out and suffered to fade for many successive times.

Other Sympathetic Inks.

Write on paper with a solution of nitrate of bismuth, and smear the writing over by means of a feather with some infusion of galls. The letters, which were before invisible, will now appear of a brown color. If the previous use of nitrate of bismuth be concealed from the spectators, great surprise will be excited by the appearance of writing, merely by the dash of a feather. The same phenomenon will take place when infusion of galls is written with, and the salt of bismuth applied | gum Arabic, 1 part, in acetic acid, 1 part, and wa afterwards.

Another. Write on a sheet of paper any sentence with a transparent infusion of nut-galls, and dip the paper in a transparent solution of the sulphate of iron. The writing, which was before invisible, will now, on a slight exposure to the air, turns quite black. A neater way of performing this experiment will be by smearing the written parts over with a feather dipped in the solution of the metallic salt; it may also be reversed, by writing with the salt and smearing with the infusion.

Another. If a letter be written with a solution of sulphate of iron, the inscription will be invisible, but if it afterwards be rubbed over by a feather dipped in a solution of prussiate of potassa, it will appear of a beautiful blue color.

Another. Write a letter with a solution of nitrate of bismuth, The letters will be invisible. If a feather be now dipped in a solution of the prussiate of potass, and rubbed over the paper, the writing will appear of a beautiful yellow color, occasioned by a formation of prussiate of bismuth.