Evening Republican, Volume 16, Number 208, Rensselaer, Jasper County, 30 August 1912 — Writing With invisible Ink. [ARTICLE]

Writing With invisible Ink.

There are several ways in which two persons can correspond with each other unknown to even the persons before whose eyes the very letter 1b held. For Instance, new milk may be used as ink. When dried this is invisible, but if coal dust or soot be scattered upon the paper the writing becomes legible. Diluted sulphuric acid, lemon Juice, solutions of nitrate and chloride of cobalt or of chloride of copper write colorless, but on being heated the characters written with the first two become black or brown, and the latter green. And when the paper becomes cool the wilting disappears, leaving the paper blank again. Two good invisible inks are made by saltpeter dissolved in water, and equal parts of sulphate of copper and sal ammoniac dissolved In Srater.