schoolscienceproject.blogspot.in
Invisible ink
If you ever want
to write a secret message on paper, simply use vinegar, lemon, or onion juice,
as the invisible ink. Write with it as usual on white writing paper. After it
dries the writing is invisible. The person who receives the letter must know
that the paper has to be held over a candle flame: the writing turns brown and
is clearly visible. Vinegar, and lemon or onion juice, cause a chemical change in
the paper to a sub- stance’ similar to cellophane. Because its ignition
temperature is lower than that of the paper, the parts written on singe.
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