Science

Quicksilver, Alchemy & Faraday's Motor – Part 2 with Andrew Szydlo

Royal Institution
Royal Institution•Apr 22, 2026

Why It Matters

Understanding Torricelli’s mercury experiment reveals the origin of atmospheric pressure measurement, a cornerstone of modern engineering, meteorology, and vacuum technology.

Key Takeaways

  • •Mercury reacts with nitric acid, producing nitrogen dioxide gas.
  • •Ammonia neutralizes nitrogen dioxide, forming harmless ammonium nitrate fumes.
  • •Torricelli used mercury columns to measure atmospheric pressure (≈76 cm).
  • •Early suction pumps struggled beyond 10 m due to air pressure limits.
  • •The experiment proved vacuum existence, challenging Aristotle’s continuous matter theory.

Summary

The video demonstrates a classic chemistry demonstration where elemental mercury is dissolved in concentrated nitric acid, generating nitrogen dioxide gas. The brown fumes are captured and neutralized with dilute ammonia, yielding white ammonium nitrate smoke, while the reaction’s by‑product, mercury nitrate, remains in solution.

The presenter then shifts to the historic Torricelli vacuum experiment, explaining how early suction pumps could only lift water about ten meters. By substituting water with dense mercury, Torricelli measured a column height of roughly 76 cm, the first quantitative record of atmospheric pressure and the first recognition that air has weight.

Key excerpts include Torricelli’s 1644 letter describing the mercury column as “one L and a quarter and a finger more,” and the broader philosophical debate between Aristotle’s continuous‑matter view and the emerging particle theory that allowed for true vacuums. The demonstration underscores how a simple mercury column resolved a centuries‑old mystery about why suction fails at higher elevations.

The implications are twofold: it illustrates the experimental roots of modern fluid dynamics and atmospheric science, and it highlights how a seemingly obscure alchemical practice laid groundwork for the physics of pressure, vacuum, and engineering solutions still used in mining and pump design today.

Original Description

Welcome to Part 2 — if you haven't watched Part 1 yet, we'd recommend starting there. Andrew Szydlo's lecture on mercury was so full of experiments, stories, and surprises that we've released the whole thing across two full hours rather than cut a single moment. We hope you enjoy every second.
Watch Part 1 here: https://youtu.be/LlMnU73PPE8
This talk was filmed at the Ri on Saturday 21st March 2026.
Mercury has fascinated us for thousands of years — found even in Egyptian tombs from 1500 BC. Known as 'quicksilver', its unusual appearance as a beautiful, dense, shiny silver liquid led to the belief that it possessed magical properties, and it was used in both medicine and alchemy. Groundbreaking discoveries have been made using mercury: from the first ever vacuum in the 17th century, to the first electric motor built by Faraday right here at the Ri.
Andrew Szydlo brings mercury to life with a host of extraordinary experiments, illustrating its remarkable properties. Mercury's compounds produce spectacular and colourful chemical reactions, and it can even be frozen with liquid nitrogen and turned into a hammerhead — with dramatic results. These experiments, and other surprises throughout the lecture, will amaze and delight curious minds of all ages.
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Andrew Szydlo is a chemist and secondary school teacher at Highgate School, well-loved by pupils and Ri attendees alike. He has given public lectures around the country, appeared on TV shows, and has become a popular part of the Ri's YouTube channel — with his videos amassing over 16 million views in total.
When Andrew started giving chemistry lessons to friends some 50 years ago, he would bring a pocket-full of chemicals to illustrate the principles of chemistry. Today, those lessons have evolved into full demonstration lectures given to audiences in a wide variety of locations. Over the past 40 years he has given over 800 talks, in addition to teaching chemistry full-time at Highgate School in London. He is now an outreach teacher, still based at Highgate School, visiting around 50 schools in London every year. The Royal Society of Chemistry included Andrew as one of their 175 Faces of Chemistry.
Chapters:
0:00 Mercury Reacts with Nitric Acid
4:15 The Most Important Experiment in Science: Torricelli's Vacuum
5:02 How Suction Works: The Syringe Demo
6:29 The Stirrup Pump in Action
7:40 Why Mines Flooded & the Problem That Stumped Galileo
13:20 Recreating Torricelli's Experiment with Mercury
16:18 The First Measurement of Atmospheric Pressure
17:43 Vacuum, Aristotle & the Birth of Atomic Theory
18:23 Pascal Takes the Barometer up a Mountain
20:32 Mercury Barometers & Weather Forecasting
21:53 Mercury's Place on the Periodic Table
24:50 Mercury's Unique Emission Spectrum
27:55 Mercury Vapour Lamps & Fluorescent Tubes
31:03 UV Light & Phosphorescence Demonstration
32:55 Mercury Nitrate & Colourful Chemical Reactions
37:31 The Iodide Clock Reaction
40:26 How Mercury Led to the Discovery of Oxygen
43:24 Lavoisier & the Composition of Air
45:23 Faraday's Electric Motor — Demonstrated in the Original Room
46:47 Ode to Mercury: A Poem to Close
51:45 The Grand Finale: Mercuric Fulminate Explosion
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