Drinking Bird / Dippy Duck / Dipping Duck

Drinking birds, also known as dippy birds and dipping birds,[1] are toy heat engines that mimic the motions of a bird drinking from a fountain or other water source. It is sometimes incorrectly considered a perpetual motion device.


Construction and materials
A drinking bird consists of two glass bulbs joined by a glass tube (the bird's neck). The tube extends nearly all the way into the bottom bulb, and attaches to the top bulb but does not extend into it. The space inside the bird contains a fluid, usually colored. The fluid is typically dichloromethane, also known as methylene chloride.

Air is removed from the apparatus during manufacture, so the space inside the body is filled by vapor evaporated from the fluid. The upper bulb has a "beak" attached which, along with the head, is covered in a felt-like material. The bird is typically decorated with paper eyes, a plastic top hat, and one or more tail feathers. The whole setup pivots on an adjustable crosspiece attached to the neck.

Despite the drinking bird's appearance and classification as a toy, some safety considerations apply. Early models were often filled with highly flammable substances. The fluid in later versions is nonflammable. Dichloromethane can irritate the skin on contact, and the lungs if inhaled; it is a mutagen and teratogen, and potentially a carcinogen. The intact toy is leakproof and completely safe, but if broken hazardous dichloromethane is released. Dichloromethane evaporates quickly; good ventilation after a spill will dilute and disperse the vapor.


Physical and chemical principles
The drinking bird is an interesting exhibition of several physical laws and is therefore a staple of basic chemistry and physics education. These include:

The combined gas law, which establishes a proportional relationship between temperature and pressure exerted by a gas in a constant volume.
The ideal gas law, which establishes a proportional relationship between number of gas particles and pressure in a constant volume.
The Maxwell–Boltzmann distribution, which establishes that molecules in a given space at a given temperature vary in energy level, and therefore can exist in multiple phases (solid/liquid/gas) at a single temperature.
Heat of vaporization (or condensation), which establishes that substances absorb (or give off) heat when changing state at a constant temperature.
Torque and center of mass
Capillary action of the wicking felt.