Drinking bird

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Drawing of two Drinking Birds.

Drinking birds are a thermodynamically powered toy heat engine. They are also known as happy birds, dippy birds, tippy birds, sippy birds, sipping birds, dunking birds, and tipping birds.

Contents

1 Construction and materials
2 Physical and chemical principles
3 How it works
4 The drinking bird in popular culture
5 External links
6 See also

Construction and materials

A drinking bird consists of two glass bulbs, joined by a tube (the bird's neck). The tube extends nearly all the way into the bottom bulb but does not extend into the top. The space inside is typically filled with coloured dichloromethane (also known as methylene chloride).

Air is removed from the apparatus, so the space inside the body is filled by dichloromethane vapour. 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 blue top hat (plastic) and a single green tail feather. The whole setup is pivoted on a variable point on the neck.

Despite its classification and appearance as a toy, there are safety considerations. Early models were often filled with highly flammable substances. New versions alleviate this concern by employing dichloromethane, which is nonflammable and not particularly toxic - but dichloromethane can irritate the skin and lungs and is a mutagen and teratogen and is potentially a carcinogen. This does not render the bird unsafe, but owners should exercise caution not to break the toy, especially when displaying it near children and animals.

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 an inverse relationship between temperature and pressure exerted by a gas in a constant volume.
The ideal gas law, which establishes an inverse 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 (give off) heat when changing state at a constant temperature.

How it works

The drinking bird is basically a heat engine that exploits a temperature differential to convert heat energy to kinetic energy and perform mechanical work. Like all heat engines, the drinking bird works through a thermodynamic cycle. The initial state of the system is a bird with a wet head oriented vertically with an initial oscillation on its pivot.

The cycle operates as follows:

The water evaporates from the head (Maxwell-Boltzmann distribution)
Evaporation lowers the temperature of the glass head (heat of vaporization)
The temperature drop causes some of the dichloromethane vapour in the head to condense
The lower temperature and condensation together cause the pressure to drop in the head (ideal gas law)
The pressure differential between the head and base causes the liquid to be pushed up from the base.
As liquid flows into the head, the bird becomes top heavy and tips over during its oscillations.
When the bird tips over, the bottom end of the neck tube rises above the surface of the liquid.
A bubble of vapour rises up the tube through this gap, displacing liquid as it goes
Liquid flows back to the bottom bulb, and vapour pressure equalizes between the top and bottom bulbs
The weight of the liquid in the bottom bulb restores the bird to its vertical position

If a glass of water is placed so that the beak dips into it on its descent, the bird will continue to absorb water and the cycle will continue as long as there is enough water in the glass to keep the head wet. However, the bird will continue to dip even without a source of water, as long as the head is wet, or as long as a temperature differential is maintained between the head and body. This differential can be generated without evaporative cooling in the head -- for instance, a heat source directed at the bottom bulb will create a pressure differential between top and bottom that will drive the engine. The ultimate source of energy is heat in the surrounding environment -- the toy is not a perpetual motion machine.

The drinking bird in popular culture

Due to the brilliance of the harmony of scientific precision that allows it to function, and its totally hypnotic, captivating, mesmerising bobbing up and down, the bird was an instant hit upon its creation and achieved near iconic status. It has even "cameoed" in the American TV show The Simpsons, in the episodes "Brother Can You Spare Two Dimes?" and "King-Size Homer". In the former episode, the drinking bird is used by Homer's half-brother Herb Powell as an example of a great invention. In the latter episode, Homer uses the drinking bird to operate the Y key (for "yes") on his work-at-home computer that controlled the necessary venting of gas for the nuclear power plant. Unfortunately, Homer neglects to check on the bird and it falls over, creating a critical situation in the area under Homer's control.

A drinking bird also appears in the 1951 Merrie Melodies cartoon "Putty Tat Trouble". Tweety Pie spies one "drinking" from a glass and, mistaking it for a real bird, asks if he can join it. Tweety mistakes the toy's bobbing motion for a nod of assent and joins it, imitating its back-and-forth movement exactly. Shortly, Sam, another cat who is fighting with Sylvester over Tweety, swallows the drinking bird by mistake, and his body then uncontrollably mimics the same bobbing motion.

Drinking bird

Construction and materials

Physical and chemical principles

How it works

The drinking bird in popular culture

External links

See also