Cryptography is familiar to our readers. On the day of entertaining facts (July 31), the guys told themselves about the properties of some liquids that can appear on paper.

The librarian explained to small researchers that some substances that are contained in milk or lemon juice under the action of heat are destroyed more quickly than the paper itself lights up. In this chemical process, combustion products are released. Using this knowledge, you can make invisible ink for secret messages.

By the sympathetic inks were used in ancient times: the secret agents of Ivan the Terrible wrote their reports with onion juice, the letters became visible when the paper was heated; Lemon juice or milk was used for cryptography.

The guys watched the experiment with interest, and watched videos about experiments with water, soda and sugar with enthusiasm.