The Origins of the Faraday Constant

The tale of the Faraday constant, now a staple in scientific discourse, is rooted in a simple device that anyone can construct at home, the genius of Michael Faraday, and an honor that rivals a Nobel Prize.

At the dawn of the 19th century, a surge of interest in chemical research emerged. Pioneers such as Antoine Lavoisier sparked what many call “the chemical revolution,” establishing chemistry as a respected field of science. Meanwhile, John Dalton was formulating theories about atomic structure, and Alessandro Volta introduced the first battery.

The latter invention, known as the “voltaic pile,” is pivotal in this narrative. Volta's creation was inspired by Luigi Galvani’s experiments with electrical circuits that stimulated muscle movement. The “voltaic pile” is quite literally a stack of alternating zinc and copper (or zinc and silver) discs, separated by cloth soaked in saltwater. This device can be built at home and used to power small devices—something I have tried myself and will detail in a future post.

Interestingly, the term "piles" also refers to a rather uncomfortable condition in British slang. Here’s a look at a replica of the voltaic pile.

Before the advent of the voltaic pile, scientists had limited options for generating a stable electrical current. The Leyden jar was the closest alternative, but it was far less effective than Volta's invention. This new capability sparked a frenzy among scientists, shifting their approach from “let’s burn this and see what happens” to “let’s electrify this and see what happens” almost overnight.

The shift in methodology was exemplified by Humphry Davy, a notable figure in this era. I won’t delve into his story here, but he certainly embraced the experimental spirit of electrification. Through his explorations, Davy discovered elements such as sodium, potassium, barium, strontium, calcium, and magnesium. More significantly, he introduced Michael Faraday, the namesake of the Faraday constant, into the scientific community. Davy mentored Faraday, taking him on a sort of scientific pilgrimage, and Faraday eventually became one of the most influential scientists of his time.

Michael Faraday (1791–1867) published an extensive body of research that remains accessible to contemporary chemists. It’s astonishing to read the works of a scientist from nearly 200 years ago, almost like a journey through time. For those interested, you can explore his original studies on electricity from 1831 here.

Throughout his investigations, Faraday formulated the “Laws of Electrolysis.” Don’t let the term “electrolysis” intimidate you; it simply refers to the process of reintroducing electrons to a substance that has lost them—typically using a battery. For instance, rust consists of iron atoms missing three electrons each. By applying electricity to rust with a battery, the iron can regain those electrons and revert to its elemental form. This is a simplified explanation, but it captures the essence of electrolysis, and it’s an experiment you can perform at home, by the way.

From his experiments, Faraday deduced that the degree of electrolysis occurring is directly related to the quantity of electricity applied. In simpler terms, the extent of electrolysis equals a constant multiplied by the amount of electrical charge used. The Faraday Constant (“F”) can be derived from this relationship. However, the formal recognition of both the term “Faraday Constant” and its numerical value (96,485) didn’t appear in scientific literature until 1909.

After reviewing Faraday’s publicly available documents, I found no record of him calculating the numerical value of his namesake constant. While it’s possible that the value was known, it seems it was expressed differently in that era. For instance, Lord Rayleigh conducted precise experiments on the electrolysis of silver, reporting the mass of silver electrolyzed per unit of electrical charge. When the molar mass of silver was divided by this figure, it yielded a value of 96,489—a remarkably close approximation to today’s figure, especially considering the measurement techniques available in the 1880s.

Instead of using F in their calculations, scientists of that time likely applied the ratio of silver’s molar mass to its electrochemical equivalent. However, the term “Faraday” didn’t appear in chemical literature until Jean Perrin referenced a value of 96,550 as a “faraday” in his 1909 paper “Mouvement Brownien et Réalité Moléculaire.” This paper also marks the first mention of Avogadro’s Number. It’s intriguing to think that two of science’s most significant constants were introduced by the same individual in a single publication.

What was Perrin thinking as he penned those words? I often created names for molecules and constants during my PhD, and I remember one instance where I whimsically dubbed an association constant “K???”—a moment of personal pride, though my advisor was less impressed.

I like to imagine that Perrin never anticipated he would be naming not just one, but two vital constants in chemistry and physics. Thanks to him, Faraday’s legacy has become an integral part of everyday science. However, Faraday’s contributions extend beyond just this constant. Upon joining the Royal Society, he initiated a series of evening lectures known as the “Friday Evening Discourse.” These lectures have gained a legendary status and are considered a prestigious opportunity for any aspiring scientist. Presenting on your area of expertise in the same esteemed setting as Faraday, Dewar, Rutherford, Bragg, and others is regarded as one of the highest honors in the scientific community, alongside receiving a Nobel Prize.

As I reflect on this legacy, I can’t help but ponder my own contributions to science...

Chapter 2: The Impact of the Faraday Constant

In the video "19.3b Using the Faraday constant - YouTube," explore how the Faraday constant is applied in various scientific calculations and its significance in electrochemistry.

The video "A.2 Faraday constant (SL) - YouTube" provides a comprehensive overview of the Faraday constant, its historical context, and its relevance in modern science.