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Pulse glass filled with magenta liquid, Europe, 1770-1900

Invented by Benjamin Franklin (1706-90), an American politician and natural philosopher in 1768, this object is known as a pulse glass. The magenta coloured liquid is sealed in the glass, creating a vacuum. When one of the glass balls is held in a person's hand, the liquid boils. Franklin viewed his invention as an intellectual curiosity.

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Glossary: pulse glass

An instrument consisting of a glass tube with terminal bulbs, containing ether or alcohol, which the heat of the hand causes to boil - so called from the pulsating motion of the liquid when thus warmed. Using a pulse glass in an experiment demonstrates Charles' law, that the volume of a given amount of dry ideal gas is directly proportional to the temperature if the amount of gas and the pressure remains fixed.