The Art of Galvanizing

David HookScience History

Oil painting of Luigi Galvani

Luigi_Galvani,_oil-paintingThis is the first post in a series of blogs about famous scientists who have contributed to our knowledge of electricity and electronics. Every month we will choose one scientist to highlight, and this month I chose Luigi Galvani because today is his birthday.

 

Luigi Galvani, born September 9th , 1737 was a prominent scientist of his era and is known as the father of bioelectricity. Born in Bologna, Italy to a doctor father he went on to study medicine and philosophy in school. He ultimately became a professor at the University of Bologna and conducted innovative research on animal electricity and what would eventually become known as the process of galvanization.

 

As one story goes, he accidentally discovered that muscles react to electricity as he held the leg of a dead frog between a bronze wire and an iron wire. As he did so, the leg suddenly contracted due to the current flowing through the nerves connected to the muscles. He was convinced after repeating the experiment multiple times that this was evidence for ‘animal electricity’, that animal cells generate electricity which is their life force. We now know that the current flow was not due to electricity being generated by the dead animal, but instead due to the potential difference between two metals.

 

In order to disprove Galvani’s theory of ‘animal electricity’, Alessandro Volta ran experiments to artificially recreate the effects seen in the frog leg and invented the first battery, now called the voltaic pile. He showed that when two different metals, such as copper and zinc are connected on one end but then separated on the other end by a porous membrane in salt solution then a small voltage is generated.

 

This is because the two different metals have their own unique oxidation and reduction potentials – the voltage at which they become ions or revert to metals. When two metals with different potentials are connected, there is a potential difference which is another way of saying voltage. However, this voltage can only flow through if the metals are able to oxidize and reduce. This is why they are submerged in a salt solution and separated by a salt bridge that only allows certain ions through.

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In the case of copper and zinc, the salt solution already contains copper and zinc ions but the salt bridge prevents metallic cations from passing through. As the metals are connected, zinc metal will oxidize into zinc ions and produce electrons that flow to the copper electrode. The electrons meet copper ions in solution and reduce the ions to copper metal atoms which gather on the surface of the electrode. The electron flow is registered above as the voltage.

 

Galvani also discovered something we now know to be true, which is that our nerves conduct electricity throughout our bodies to control our muscles. Just like Galvani, today we use electrodes to detect this electricity with Electroencephalographs (EEG). Galvani’s experiments also indirectly inspired Mary Shelly’s Frankenstein, where she based the monster’s iconic birth on the theory of “animal electricity”.

 

This is why Luigi Galvani’s name has gone down in history as a pioneer in the field of electrochemistry and his experiments contributed to our current knowledge of electricity, batteries, and neuroscience. The electrochemical setup described above still bears his name and is called a Galvanic cell because he prompted Volta to disprove ‘animal electricity’.