The transformation of water into steam
This tool designed by Leonardo is used to measure the expansion and pressure of steam. The device consists of a container filled with cold water and covered by a lid balanced by a counterweight. When the fire is lit, the water evaporates and pushes on the lid. The whole phenomenon can be observed though an elastic and semitransparent window cut in the side of the container and made out of animal bladder.
Codex Leicester, sheet 10 r.