Benjamin Franklin was born yesterday, on January 17, 310 years ago. Here in Philadelphia, where he lived and worked, Franklin’s name is plastered on everything from street signs, to bridges, to bars–and for good reason. In addition to experimenting extensively with electricity and printing multiple newspapers, Franklin helped found the United States of America by uniting the colonies and enlisting the aid of the French. (For more about his trip to France, check these out images in CHF’s collection of rare books.) But what does Franklin have to do with the weird purple contraption pictured above?
Franklin was a chronic inventor. Many of the technologies he created changed the way people lived. Bifocal lenses made it possible for people with impaired vision to read a newspaper or spot a ship on the horizon. Lightning rods protected homes from catching fire during thunderstorms. The effect of other inventions was not as dramatic, such as this Glass tube filled with purple liquid that Franklin called a Pulse Glass. Franklin himself thought of it as nothing more than a neat party trick when he invented it in 1768.
Franklin built the Pulse glass by filling a glass tube with water or alcohol, sucking out all the air, and vacuum sealing it. He found that if he held one end of a pulse glass in the palm of his hand, the other end heated up and rapidly boiled within seconds. The spooky boiling was caused by the laws of thermodynamics: inside a vacuum, pressure is so low that even the tiny amount of heat generated by Franklin’s hand was enough to transform the liquid into gas, shooting it from one end to the other.
Today, the pulse glass is sometimes used to demonstrate physics in classrooms. You might be more familiar with it as the “sipping bird,” that perpetual motion toy with a top hat that endlessly bobs its head up and down as if it were silently affirming Franklin’s legacy.
Images: Wellcome Images, GIPHY