[8] Air is removed from the apparatus during manufacture, so the space inside the body is filled by vapor evaporated from the fluid.
[12] By considering the difference between the wet and dry bulb temperatures, it is possible to develop a mathematical expression to calculate the maximum work that can be produced from a given amount of water "drunk".
The evaporation of water is an endothermic process requiring the input of thermal energy or a positive enthalpy flow from the environment.
Since a spontaneous process requires a negative change in Gibbs free energy, the positive enthalpy has to be overcome by the large entropy increase.
[15] In 1872, the Italian physicist and engineer Enrico Bernardi combined three Franklin tubes to build a simple heat motor that was powered by evaporation in a way similar to the drinking bird.
A Chinese drinking bird toy dating back to 1910s~1930s named insatiable birdie is described in Yakov Perelman's Physics for Entertainment.
[1] The book explained the "insatiable" mechanism: "Since the headtube's temperature becomes lower than that of the tail reservoir, this causes a drop in the pressure of the saturated vapours in the head-tube ..."[1] It was said in Shanghai, China, that when Albert Einstein and his wife, Elsa, arrived in Shanghai in 1922, they were fascinated by the Chinese "insatiable birdie" toy.
Drinking birds have been featured as plot elements in the 1951 Merrie Melodies cartoon Putty Tat Trouble and the 1968 science fiction thriller The Power.
In S4E11 of the comedy series Arrested Development, a delusional character hears the voice of God speaking through a drinking bird.
[24] In Australian contemporary playwright John Romeril's play The Floating World, drinking birds are a symbolic prop which represent the progression of Les' insanity.
In 2003 an alternative mechanism was devised by Nadine Abraham and Peter Palffy-Muhoray of Ohio, USA, that utilizes capillary action combined with evaporation to produce motion, but has no volatile working fluid.
Instead it utilizes a combination of capillary action, gravitational potential difference and the evaporation of water to power the device.