Nitric acid: from historical aqua fortis to modern fertilisers and explosives

Overview

In this Chemistry World episode nitric acid is presented as a remarkably versatile chemical with a rich history, from its early mentions in medieval writings to its central place in modern industry. The discussion covers how it is made, its common concentration, and why it can appear yellow in the lab due to dissolved nitrogen dioxide.

• Nitric acid has medieval roots and was once called aqua fortis, a name that reflects its strong oxidative power.
• The Ostwald process converts ammonia and oxygen to nitric oxide and then to nitric acid, enabling large scale production.
• Most nitric acid is used for fertilisers, notably ammonium nitrate, which has transformed agriculture and also features in explosives.
• Nitrocellulose, once a major explosive derivative, also found constructive use in film stock and early photography through collodion.

Next week’s episode shifts to a different compound and introduces a green fluorescent protein story, promising another engaging science narrative.

Overview

The podcast from Chemistry World presents nitric acid as a cornerstone chemical with a long and complex history. It explains how the acid is produced and refined, and outlines its broad range of applications from agricultural fertilisers to energetic materials, while also highlighting some surprising non‑industrial uses.

Historical background and naming

The host describes nitric acid as a compound with a venerable history. Its old name aqua fortis, meaning strong water, reflects the early understanding of its strong oxidising power. The narrative notes that the term appears in 13th century writings attributed to figures such as Albertus Magnus and Raymond Lull, with possible earlier references to nitric acid in medieval or pseudo‑medieval texts. The discussion also touches on the sometimes blurred line between genuine sources and fraudulent medieval works, a reminder of the challenges in tracing the history of chemistry.

Production and properties

Since the early 20th century nitric acid has been produced on a large scale via the Ostwald process. The sequence begins with ammonia and oxygen reacting over a catalyst at high temperature, forming nitric oxide, which then reacts with more oxygen to form nitrogen dioxide. The nitrogen dioxide is dissolved in water to yield nitric acid. In industry the acid is typically dilute; concentrates reach about 68% HNO3 by weight, and the pure liquid can be collected as fuming nitric acid. Although the acid is technically colourless, dissolved nitrogen dioxide often imparts a yellow tint in lab bottles.

Reactivity and uses

Nitric acid can act as a base with strong acids such as sulfuric acid, and it is widely used in metal testing where gold is resistant to the acid while many gold substitutes are not. Its strong oxidising power makes it a key reagent in rocket fuels and in the production of nitrates used in energetic formulations. In industry the acid helps provide NO2 groups that stabilise or activate energy release in organic compounds, enabling rapid combustion and explosive reactions. A large portion of production—roughly 80%—is directed toward making fertilisers, especially ammonium nitrate, which has dramatically reshaped agricultural productivity while also playing a role in explosive devices in various contexts. The discussion notes the dual character of nitric acid in society, balancing its benefits for food production against concerns about environmental impact and misuse in explosives.

Nitrocellulose and film chemistry

Nitrocellulose is highlighted as a major derivative of nitric acid. It was used in film stock and as a matrix for silver salts in early photography, notably in collodion processes used by photographers such as Edward Muybridge. The narrative includes a reflection on the intimate link between chemistry and the craft of photography, quoting Muybridge about chemists being their own chemists in the era of glass plates and dipping baths.

Societal context and takeaway

The episode concedes that nitric acid carries a negative taint because of its association with explosives and environmental concerns related to nitrates and greenhouse gas emissions. Yet it also acknowledges the essential role of fertiliser chemistry in sustaining global food supplies. The host awards nitric acid a score of 8 out of 10 for its historical significance, versatility, and broad industrial impact, while noting that its societal footprint is complex and nuanced.

GFP teaser

The podcast then pivots to next week’s story about the green fluorescent protein, illustrated through a short narrative about Osamu Shimomura and the science surrounding GFP, setting the stage for another science‑forward discussion.

Conclusion

The episode closes with the standard sign‑off from the Chemistry World team, inviting listeners to return for the next installment on a different compound and its story.