Michael Faraday · Science
Faraday’s laws of electrolysis - chemical change is exactly proportional to the electricity passed - together with the vocabulary he coined (electrode, ion, anode, cathode) and his proof that there is only <em>one</em> electricity, whatever its source.
Pass an electric current through water (with a little acid) and it decomposes: hydrogen bubbles off one wire, oxygen off the other. Pass it through molten or dissolved salts and metals plate out. This is electrolysis - electricity tearing chemical compounds apart. Humphry Davy, Faraday’s own master, had used it spectacularly around 1807 to isolate potassium and sodium for the first time, ripping these violent new metals out of compounds no ordinary chemistry could break. But no one knew the rule. How much decomposition does a given amount of electricity produce? Is there a lawful, numerical relationship between the quantity of electricity and the quantity of chemical change? Faraday, in the early 1830s, set out to measure it with his characteristic precision - and found a law of beautiful exactness that tied electricity and matter together by number for the first time.
Then came the deeper law. Faraday found that the same quantity of electricity liberates amounts of different elements in proportion to their chemical ‘equivalent weights’ - the very combining proportions that ordinary chemistry had already found. To free one unit of hydrogen, or the equivalent amount of oxygen, or of a given metal, took a fixed, definite quantity of electricity. This Second Law tied electricity directly to the atomic theory of matter: it suggested that each atom carries a definite, fixed portion of electricity, a natural unit of charge. Faraday did not name the electron - that waited until 1897 - but his laws point straight at it. Decades later, dividing his fixed quantity of electricity by the number of atoms in it gave the charge on a single electron. In measuring the chemistry of electricity, Faraday had, without knowing it, weighed the atom of electricity itself.
By the 1830s electricity came from a confusing variety of sources, and many suspected they were different fluids: ‘common’ electricity from friction machines, ‘voltaic’ electricity from batteries, ‘animal’ electricity from electric eels, ‘thermo’ electricity from heated junctions, and the ‘magneto’ electricity Faraday himself had just wrung from moving magnets. Were these five electricities, or one? Faraday settled it experimentally. He showed that electricity from every source produced the same effects - the same spark, the same physiological shock, the same magnetic deflection, the same chemical decomposition - differing only in quantity and intensity, never in kind. His conclusion was momentous in its simplicity: there is only one electricity, whatever its source. This unification, like his welding of electricity and magnetism, sprang from Faraday’s instinct for the deep singleness of nature, the same instinct that drove his lifelong hunt for links among electricity, magnetism, gravity, and light.
This is the opening of the lesson. The rest — the dialogue, the primary source, and the recall — is in the app.
You learned Faraday’s two laws of electrolysis (chemical change proportional to charge, and to equivalent weight), the theory-neutral vocabulary he coined with Whewell, and his proof of the identity of electricities from all sources. Explain these and why they pointed toward an atom of electricity.
Leads to Francis Bacon.
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