Hand boiler
A hand boiler or love meter is a glass sculpture used as an experimental tool to demonstrate Charles's Law and vapor-liquid equilibrium or as a collector's item to measure love. It consists of a lower bulb containing a volatile liquid and a mixture of gases that is connected usually by a twisting glass tube that connects to an upper or "receiving" glass bulb.
Mechanics
The colored liquid inside a hand boiler is composed of a volatile mixture of liquids that places the boiling point of the mixture to just above room temperature. [1] When a hand is placed under the bottom bulb containing the colored liquid, body heat transfers to the liquid and causes it to boil. The liquid evaporates and turns to gas, expanding with the help of body heat due to Charles's law. Because the liquid is trapped inside the bottom glass bulb and has nowhere to go, the expanding gas pushes the liquid upwards through a twisting glass tube into an upper receiving bulb. When the hand is released from the bottom bulb, equilibrium is able to be re-established so the gas condenses into liquid again and the liquid that was forced upwards into the receiving glass bulb flows back into the lower bulb.
Popular culture
In popular culture, hand boilers are often known as love meters because the tube that separates the upper and lower bulbs is twisted into a heart shape and the volatile liquid is colored red. Love meters are a common collector's item or a souvenir.
References
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