A drinking bird toy is a novelty item that appears to drink endlessly from a glass of water. The bird toy is powered by the evaporation of a volatile liquid inside its sealed body. When the liquid evaporates, it cools, causing changes in air pressure that make the bird dip its beak into the water, which re-prime the evaporative cooling process. This cycle repeats indefinitely as long as there is water in the glass. The liquid inside a drinking bird toy is typically methylene chloride.
How Does a Drinking Bird Work?
A drinking bird toy operates through the process of evaporation. The main body of the bird is a sealed chamber containing a volatile liquid with a low boiling point, such as methylene chloride. At the bottom of the chamber is a beak-shaped tube made of felt. The tube acts as a wick, drawing liquid up from the chamber by capillary action.
When the toy is placed near a glass of water, the liquid in the wick evaporates, cooling the air inside the chamber. This cooled air then becomes denser and sinks to the bottom of the chamber. The resulting change in air pressure forces liquid back up into the wick, causing the bird’s head to become top-heavy and tip forward, making the beak dip into the water. This wets the wick, allowing more evaporation to occur.
As the evaporating liquid cools the air further, the vapour condenses on the chamber walls. The condensed liquid then runs back down to the bottom of the chamber, making the head light and causing the bird to tip back again. This motion restarts the evaporation-cooling cycle, making the bird appear to drink perpetually from the glass.
The Thermodynamics Behind a Drinking Bird
The thermodynamic principle that drives a drinking bird toy is evaporation. When atoms or molecules transition from liquid to gas, they absorb heat from their surroundings. The evaporation of the volatile liquid in the chamber absorbs thermal energy, cooling the internal air.
Additional thermodynamics are at work inside the bird’s chamber. As evaporation cools the internal air, the vapour condenses on the chamber walls, releasing heat. Some of this heat is transferred back into the chamber by conduction through the walls, offsetting the cooling from evaporation. This creates a constant heat flux dynamic that reaches equilibrium, allowing continuous cycling of the bird.
Choosing the Right Liquid
The liquid inside a drinking bird toy needs to have the right combination of thermal properties to work properly. The ideal liquid has:
- A low boiling point, to evaporate easily at room temperature
- The right vapour pressure curve to allow condensation on the chamber walls
- Appropriate heat transfer properties to sustain the evaporation-condensation cycle
With these characteristics in mind, methylene chloride is a common choice for drinking bird toys. Other potential liquids include ether, carbon tetrachloride, and trichloroethylene.
The History of Drinking Birds
Drinking bird toys have been popular novelty items since the 1940s. The original design is credited to Miles V. Sullivan, who filed a patent in 1946. Sullivan’s design used ether as the volatile liquid. The early drinking bird craze saw the toys made from materials like glass and ceramic.
Over the decades, various manufacturers have produced additional designs and adapted the choice of internal liquid. Plastic and metal drinking birds became common. The use of methylene chloride allowed the toys to function at a wider range of temperatures. While drinking bird toys were briefly banned due to the toxicity of some liquids, methylene chloride models continue to be sold today.
1945: Miles V. Sullivan’s Original Design Patent
Miles V. Sullivan filed the first US patent for a drinking bird design in 1945. His concept involved a glass bird head connected to a glass or ceramic body chamber. The chamber contained a small amount of low boiling point ether. Sullivan described how evaporation of the ether would drive the oscillating motion, causing the bird to appear to drink perpetually.
1950s-1960s: Drinking Birds Become Popular Novelty Items
In the post-war era, drinking bird toys became popular across America and Europe. Their distinctive appearance and seemingly magical drinking motion captured public fascination. Retailers marketed affordable tabletop models made of glass, ceramic and other ornate materials. The toys became ubiquitous in workplaces and homes during this period.
1970s-1980s: Plastic Designs and Safer Liquids
As concern grew about the toxicity of liquids like ether and chloroform, manufacturers shifted to safer volatile substances. Methylene chloride became a popular choice. New plastic designs also emerged, replacing delicate glass and ceramic birds. Kitsch larger plastic models like swinging birds drinking from beer steins became popular home decor items.
Today: Drinking Birds Remain Timeless Novelties
Modern drinking bird toys retain the same amusing drinking motion that made them classic desk accessories. While methylene chloride allows the birds to function more reliably, part of their old-fashioned charm remains. Drinking birds are common souvenirs and continue to be gifted frequently, more than 70 years after their invention.
How Drinking Birds Work: Step-By-Step
The drinking bird’s perpetual motion works through a delicate balance of thermodynamic processes. Here is a step-by-step look at how it works:
- Liquid inside the bird’s chamber evaporates, absorbing heat from the air.
- Evaporative cooling makes the air density increase.
- The chilled air descends to the bottom of the chamber.
- The pressure change forces liquid up into the wick.
- The head becomes top-heavy and tips forward.
- The beak dips into the water glass.
- The wet wick allows rapid evaporation, cooling the air.
- Vapour condenses on the chamber walls, releasing heat.
- The liquid runs back down to the chamber bottom.
- The head becomes light and tips back.
These evaporative cooling-condensation cycles repeat continuously, powering the bird’s perpetual drinking motion. The system works best when the ambient temperature is in the ideal range for the chosen liquid.
Internal Chambers and Wicking Systems
Inside a drinking bird are two key components – a sealed chamber filled with a volatile liquid, and a wicking system that delivers the liquid to the beak. The chamber can have different shapes, while the wick design determines the motion of the beak.
Chamber Designs
The liquid-filled chamber inside a drinking bird is normally egg-shaped or spherical. More elaborate designs may use additional bulbs and narrow connecting tubes. The chamber can be oriented vertically or set at an angle. An angled design makes the beak motion more pronounced up and down.
Wicking Systems
Wicking systems pull the volatile liquid from the reservoir chamber up to the beak. This is done through capillary action along some combination of:
- Felt tubes
- Textile fibers
- Narrow tubing
- Porous ceramic
Gravity combines with capillary forces to move the liquid as the head tips back and forth. The wick needs sufficient surface area to provide adequate evaporation. Making the wick of porous materials like felt maximizes evaporation sites.
Typical Drinking Bird Liquids
Liquid | Boiling Point (°C) | Concerns |
---|---|---|
Ether | 34.6°C | Highly flammable and toxic |
Chloroform | 61.2°C | Toxic, suspected carcinogen |
Methylene Chloride | 40°C | Harmful if inhaled |
1,1,2-Trichloro-1,2,2-trifluoroethane | 47.7°C | Ozone depleting substance |
As the table shows, many liquids used historically in drinking birds have toxicity issues. Methylene chloride became a popular choice because it has a suitable boiling point and is less dangerous than alternatives like ether or chloroform. Proper usage also avoids inhaling vapours from the toy.
Drinking Bird Variants and Adaptations
Drinking bird toys have spawned numerous design variants and adaptations over the decades:
Larger Drinking Birds
Oversized plastic drinking birds became a kitsch decor item in the 1970s and 80s. These models might be 1-2 feet tall and use an internal bellows system to move air rather than evaporative cooling. The beak dips into a receptacle like a beer mug or fishbowl.
Bobbing Bird Pencil Holders
Small drinking bird variants were produced as pencil holders. These simple designs have a heavy weighted base with a short tube body supporting the movable head. The partial vacuum inside drives the bobbing motion.
Bottle Cap Drinking Birds
Miniature plastic drinking birds are also made to fit on top of bottle caps. They stick into the bottle and appear to drink perpetually as condensation forms. The bottle needs to be chilled to provide enough condensing moisture.
Beer Can Drinking Birds
Bigger plastic drinking bird designs are sized to dip their beaks over a beer can. These novelty items mimic the appearance of drinking from the can as condensation drips down the sides. Colorful liquid can be added to the bird’s head to resemble beer sloshing around.
Promotional Drinking Birds
Drinking bird-style toys are often customized for promotional giveaways. Instead of the traditional glass and bird motifs, they are shaped like products, brands or characters. The internal thermodynamics remain the same, with the novelty shape dipping down perpetually.
Troubleshooting Problems With Drinking Birds
While drinking bird toys have simple workings, their motion can become erratic or stop entirely if something goes wrong. Troubleshooting involves checking different elements of the system:
Not Enough Liquid
One common problem is that the chamber runs out of volatile liquid. This can happen over years of operation as the liquid slowly evaporates away. Topping up the body with more liquid will resume the motion.
Air Pressure Imbalance
If changes in temperature or humidity affect the vapor pressure differential inside the bird, air pressures may prevent motion. Gently warming or cooling the toy could help restore the convection cycle.
Wick Obstruction
Blockages, accumulations or drying of the wick system can interrupt the capillary action that feeds liquid to the head. Cleaning and removing obstructions in the wick may improve liquid transport.
Mechanical Failure
Over time, material fatigue or gradual leaks can lead to failure of the seals and joints. Repairing drinking birds requires replacing gaskets and seals or cementing fractures to make the chamber airtight again.
Conclusion
Drinking bird toys remain captivating curiosities that demonstrate amazing physics. The heat transfer properties of evaporating liquids power perpetual motion inside these sealed toys. Understanding the thermodynamics involved helps explain why drinking birds dip endlessly to take sips of water. Careful design and material selection allow drinking birds to operate reliably for years, remaining decorative staples of workplaces and homes.