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Wednesday February 27, 2019 at 10:58am Age: 85 days
Category: Middle School, District


Jennifer Bittner’s seventh-grade social studies class made connections to the Revolutionary War’s spy network and kindness during a recent in-class project.


The project was an interesting spin on learning about the Revolutionary War which also involved a bit of science.  


“The lesson revolved around spy networks that developed during the Revolutionary War and whose activities and actions have influenced our modern day intelligence networks,” she said.  “We talked about the science behind the use of secret coded messages focusing on the use of invisible ink. Students then used the different methods of invisible ink Revolutionary War spies used and wrote messages of kindness to one another. Using an iron, they applied heat to reveal those messages which will be hung on our class bulletin board called ‘Kindness is Revolutionary.’”


Getting secret messages to military leaders


British and American spies used different forms of communication to get secret messages to their military leaders during the Revolutionary War.


One form of secret writing used by both was invisible ink, Mrs. Bittner explained.  At the time of the Revolutionary War, invisible ink usually consisted of a mixture of iron salt (ferrous sulfate) and water.


“The secret writing was placed between the lines of an innocent letter,” she told the class. “If the enemy got a hold of the secret message, they wouldn’t know because the it would look like a regular letter. One way the secret message could be revealed was by placing the letter over a source of heat, such as a candle. Another way the message could be revealed was by treating it with a chemical such as sodium carbonate.”


She told the class that British spies would mark their letters written in invisible ink with a “F” for fire and “A” for acid, so that the reader knew whether to use heat or a chemical solution to reveal the letter’s message.


Tying famous spies to science, communication and kindness


Famous spies --- Nathan Hale (an American who died spying on the British), Benedict Arnold (an American unhappy over not receiving a promotion from the Army who became a British spy) Benjamin Tallmadge (leader of George Washington’s super-secret Culper spy ring) and James Armistead (the most well-known African-American spy who was an American spy even though he appeared to be a British spy) --- were known to communicate this way.  


But, letters written in invisible ink needed special care. Water or other liquids could smear the invisible ink and make it impossible to read.  Paper was also either heated by flame or treated with acid, so the paper was very brittle and dark.


Writers used lime juice as well as milk, vinegar, lemon juice and anything acidic to weaken the fibers of the paper. When heat was applied to their documents, the weakened fibers turned brown faster than the fibers that are not weakened. That’s how their messages became visible.  


Mrs. Bittner also told the class that spies used sympathetic inks, which means spies wrote with one chemical and the writing would disappear. By applying a second chemical, a chemical reaction would occur, and the writing would be made visible again.


Students used lemon juice, baking soda and an iron as a means of crafting their kindness messages and bringing them to life. 


'It's cool to learn about what they did before us'

“It’s really interesting,” said student Michael Zechewytz. “We’re doing what they did ‘back then.’ It’s cool to learn about what they did before us.”


Michael’s kindness message was “You are a great friend,” made visible once the heated iron provided the chemical reaction to reveal his words.  


“I’ll tell my dad, tonight, that we wrote in invisible ink,” he said. “I think it’s good that we had a chance to write a message in invisible ink. Another good lesson from this is that we should always be nice to each other and we shouldn’t be mean.”