David Newnham has a fruitless stab at invisible writing
Is it me, or is there something wrong with the lemons you buy these days? Somehow, I just can’t get my lemon juice to burn.
It all began with a school book sale. My son pointed to a volume called Horrible Science on whose cover a cartoon chemist was merrily blowing himself up. The inclusion in the price of two magnets and a green balloon proved irresistible.
The “book” turned out to be a collection of cards, each descibing an experiment. There was “Dare you discover how to make artificial sick?” and “Dare you discover how stomach acid protects guts?”, the authors being at some pains to justify the term “horrible”.
After a quick run through the alternatives (where was I going to get a protractor, some corrugated cardboard, a bottle of rennet and an old shoebox at 5.30 in the evening?), I opted for good old invisible writing.
“Dare you discover lemon’s burning secret?” It was worth a try. “What you need” seemed simple enough - no square glass jars or yeast or pieces of black card, just half a lemon, a cup and a sheet of paper. The list included “an empty fountain pen”, but I decided a paint brush would do as well (when did you last try removing ink from a dried-up fountain pen?). “What you do” was also straightforward. Squeeze lemon, write with juice, hold paper over warm radiator, watch as writing slowly appearsI Except that it didn’t. After 10 minutes with the radiator, we tried searing it on a storage heater.
Eventually my son announced: “You lied to me, Daddy,” and surrendered himself to the more reliable delights of children’s television. “Don’t blame me!” I called after him. “I was just doing what the card said.” And then I looked more closely at what the card did say.
After stating that “the heat makes the lemon juice darker so you can see it”, the authors explained: “Lemon juice burns at a lower temperature than paper. This fact is very useful for sending your own secret messages.” Lemon juice burning in front of a “warm radiator”? Clearly these cards not only looked dumb - they were dumb.
Oh well, it was 6 o’clock and I still had half a lemon. For what I had in mind, I would need: one glass, one measure of gin, one bottle of tonicI
