Today’s Google Doodle commemorates the 270th anniversary of Alessandro Volta’s birth. Volta was a pioneer in electricity and batteries whose contributions are so noteworthy that our unit of current, the volt, is named after him.
But Volta’s discoveries are particularly important to anyone who has metal amalgam fillings, or, really, any metal restorations in the mouth.
Seeing Past Animal Electricity
Volta didn’t discover the existence of electric currents between metals. That honor goes to his contemporary Luigi Galvani, who gave his name to galvanic currents and galvanized metal. Galvani discovered that if he placed a frog’s leg across two plates of dissimilar metals, the leg would twitch. Galvani believed that the twitching was caused by the existence of an animal electricity within the leg. Because of his discovery, we call electricity flowing between dissimilar metals a galvanic circuit.
Volta initially accepted this explanation, but later came to believe that the leg was actually acting as a sort of primitive voltmeter, just measuring the current created by the two metals. He was then able to show this was the case using a different measurement technique.
He further realized that if he placed successive units of dissimilar metals together, he could increase the potential of the currents, and eventually gave himself a significant shock using his pile of metals, which was the first primitive battery–and the reason why batteries are known as piles in many languages.
The Galvanic Series and Metal Amalgams
Later discoveries showed that the current generated by a galvanic circuit is determined by how dissimilar they are on what is now called the galvanic series. It’s rated by what is called the nobility of metals. When less noble metals and more noble metals are placed in a liquid together, they generate electricity.
Metal amalgam has a number of components that are of very low nobility, including tin, copper, and zinc. Other metals used in the mouth are much higher nobility, including gold, titanium, steel, and even silver, which is also part of metal amalgam.