How a drinking bird works

The drinking bird was invented by Miles V. Sullivan in 1945 and patented in 1946. The drinking bird was an instant hit. It is still a popular toy in the United States, as well as many other countries. It is fascinating to watch and a great way to learn about Physics and Chemistry. The drinking bird is a heat engine, using temperature differential to convert heat energy to a pressure differential with the bird. Heat engines operate through a thermodynamic cycle. It is not a perpetual motion device.

The drinking bird is made up of two hollow glass bulbs, equal in size, with a long glass connecting tube. One bulb is the head of the bird and the other is the abdomen. The drinking bird usually has two legs on a base with a pivot connection, connecting it to the long glass connecting tube. The tube extends nearly all the way in to the bottom bulb but does not continue into the top. A fuzzy, water absorbent material covers the head.

Methylene chloride, an industrial paint thinner and solvent, is the red fluid that is in the body of the bird. Methylene chloride is used because of its accelerated rate of evaporation. Methylene chloride can irritate the skin and lungs, so extreme care is advisable should the glass break. Air is removed from the glass tube and bulbs.

To operate the drinking bird, you must first wet its fuzzy head. Once the head is wet, the water starts to evaporate, causing the head to cool. The temperature decrease in the head condenses the methylene chloride vapor, decreasing the vapor pressure in the head relative to the vapor pressure in the abdomen. The higher vapor pressure in the abdomen forces fluid up into the neck and head.

As the fluid fills the head of the bird, it becomes top heavy and tips on the pivot. With the bird tipped over, the bottom end of the neck tube rises above the surface of the fluid. Vapor bubbles travel down the tube to the head allowing the fluid to drain from the head, leaving the head full of the vapor. The fluid fills the abdomen and the bird lifts his head.

The bird will continue this process so long as the head remains wet or as long as the temperature differential remains between head and body. The drinking bird will also perform quite well if you hold the bulb in your hand, using the heat from your hand to cause temperature differential.