Who Discovered Ammonia? The Salt of Ammon and a 1,900-Year-Old Naming Mistake

There are two naming mistakes sitting on the same shelf, and they are about 1,900 years apart. The first is that ammonia is named after a salt that was probably not ammonia. The second is that the jug we sell it in is labelled with the name of a molecule that does not exist. Both are worth understanding, because between them they explain almost every point of confusion buyers have about this product — what it is called, what strength means, and why two containers with different numbers on them can hold the same chemistry.

Who discovered ammonia?

Joseph Priestley isolated ammonia gas in 1774 and called it “alkaline air.” He produced it by heating sal ammoniac with quicklime and collecting the gas that came off, part of the same run of pneumatic experiments that produced his work on other “airs.” Priestley did not know what it was made of; he knew it was distinct, pungent, soluble in water to an extraordinary degree, and alkaline.

Two later steps finished the job. Torbern Bergman gave the gas the name ammonia in 1782. Three years after that, Claude Louis Berthollet established its composition in 1785, showing it to be a compound of nitrogen and hydrogen — what we now write NH₃. So the discovery is really a sequence rather than a moment: isolated 1774, named 1782, understood 1785.

Why is it called ammonia?

Because it was made from sal ammoniac — and sal ammoniac was named for a place, or a god, or a patch of sand, depending on which ancient authority you follow. Bergman coined the word in 1782 from the name of the salt his contemporaries had been distilling for decades. That salt was called sal ammoniac, and the trail behind the name runs into Roman North Africa and then goes cold.

Pliny the Elder, in Natural History XXXI, describes a salt he calls hammoniacus sal: a fossil salt found below the sand in a district of Cyrenaica. Three separate derivations of that name survive, and they do not agree:

It is worth being blunt about how thin this is. The popular telling — that the salt was scraped from soot at the Temple of Ammon and that this is definitively why we say ammonia — is one reading among several, and it is not the one Pliny himself gives. The etymology is genuinely unsettled.

What is sal ammoniac, chemically?

Sal ammoniac is the historical name for ammonium chloride, NH₄Cl — a white crystalline salt, not a liquid and not a gas. It is the feedstock, not the product: heat it with a base such as quicklime and it releases ammonia gas, which is exactly the reaction Priestley ran. That is the whole reason an ammonium chloride name ended up attached to a nitrogen-hydrogen gas.

How was sal ammoniac actually made?

In Egypt, by subliming it out of soot. This is the part of the story that is well documented and almost never told. Egypt was where sal ammoniac was first manufactured at scale and the source that supplied Europe. The process was straightforward: collect animal dung, burn it, and recover the salt from the soot by sublimation — heating it so the salt vaporises and re-condenses as crystals on a cooler surface.

Period accounts name the dung of black cattle, horses, sheep and goats. Camels are not in that list, despite being the animal the popular version of this story always reaches for. The nitrogen in the salt comes from the same place the nitrogen in any manure does — protein in the animal's diet — and the chloride comes along with it.

Was Pliny’s salt really ammonium chloride?

Probably not. This is the twist that makes the etymology a curiosity rather than a clean lineage. Herbert Hoover — the mining engineer who, with Lou Henry Hoover, produced the standard English translation and commentary of Agricola's De Re Metallica — judged that the salt Pliny described does not match the properties of ammonium chloride, and that it was likely to have been common sea salt.

Read the chain end to end and it is faintly absurd. A Roman naturalist describes a salt dug from under the sand and gives it a name. The name attaches, over centuries, to a different white salt made from burnt dung in Egypt. In 1774 an English minister heats that second salt with lime and catches a gas. In 1782 a Swedish chemist names the gas after the salt. The word we still use for one of the most important industrial chemicals on earth is inherited from a substance that was probably table salt.

What is ammonium hydroxide, and why is that name also wrong?

Ammonium hydroxide is ammonia gas dissolved in water, and there is no stable NH₄OH molecule in the bottle. Ammonia is extraordinarily soluble in water, and in solution it sits in an equilibrium: most of it stays as dissolved NH₃, while a small fraction reacts with water to give ammonium (NH₄⁺) and hydroxide (OH⁻) ions. That hydroxide is what makes the solution alkaline. The label names a compound that is really a description of a mixture.

This matters commercially, not just pedantically. Because the dissolved gas is the active species, concentration is the specification — and it is also why an open container weakens over time as ammonia escapes, and why the smell is so aggressive at strength.

Why do two suppliers quote completely different percentages for the same product?

Because the percentage can be expressed on two different bases, and they differ by a factor of about two. This is the single most expensive misunderstanding in buying aqueous ammonia, and it follows directly from the fact that ammonium hydroxide is not a real molecule.

A concentration can be quoted as NH₃ — the mass of dissolved ammonia gas per mass of solution — or as NH₄OH, notionally converting all of that ammonia into the hypothetical hydroxide. Ammonia has a molar mass of about 17.03 g/mol and NH₄OH about 35.05 g/mol, so the second number is roughly 2.06 times the first. A solution sold as 29% is the same liquid as one sold as about 58–60%, if the first is quoted as NH₃ and the second as NH₄OH.

What is ammonium hydroxide used for?

It is the standard way to add alkalinity to a water-based system without adding a metal ion. That single property explains most of its industrial uses. Sodium hydroxide raises pH but leaves sodium behind; ammonia raises pH and, being a dissolved gas, can largely leave the system again. Where a residual cation would be a contaminant, ammonia is the reagent of choice.

Cleaning and surface preparation

Ammonia is a workhorse in cleaning formulation, cutting grease and leaving little residue on glass and hard surfaces as it flashes off. Diluted solutions at the lower end of our range are typical here; the 5% and 10% products exist so formulators are not buying concentrate and water separately.

Water treatment and pH control

Ammonia is dosed for pH adjustment, and reacted with chlorine to form chloramine, which municipal systems rely on because it persists much further into a distribution network than free chlorine does. In boiler and steam-cycle chemistry it is used to raise the pH of feedwater to control corrosion, precisely because it carries no metal ion into the loop.

Electronics and precision cleaning

Dilute ammonia is a component of the standard alkaline wafer-cleaning chemistries used to strip organic residue and particles from silicon surfaces — work where trace-metal limits matter and ACS Grade earns its price. See our photonics manufacturing chemistry guide for where it sits in the sequence.

Metal finishing and patina

Ammonia vapour reacts with copper and its alloys to develop blue-green patina, which is why it appears in architectural metalwork and conservation practice as well as in studio patina work. It also serves as a complexing agent for copper and nickel in plating and etching chemistry.

Rubber, textiles and pulp

Ammonia stabilises natural rubber latex against premature coagulation during shipping and storage, and is used in textile and pulp processing for pH control and as a swelling agent. These are high-volume, cost-sensitive uses, and they run on Technical Grade.

What should you never mix ammonium hydroxide with?

Never mix it with bleach or any hypochlorite product. Ammonia and sodium hypochlorite react to form chloramine vapours, which attack the airways; this is the single most common way people are injured by two ordinary cleaning products in a confined space. It is also worth keeping ammonia away from strong acids, which react vigorously, and away from oxidisers generally.

Which concentration and grade should you buy?

Pick the concentration your process needs and the grade your documentation needs — they are two separate decisions. Concentration sets how much ammonia is in solution; grade sets how tightly the impurities are controlled and what paperwork comes with it. Buying 29% ACS Grade when a process needs 10% Technical Grade means paying for purity and for water you then have to dilute anyway.

Technical Grade is the right default for cleaning formulation, pH adjustment, water treatment chemistry and general industrial use. ACS Grade is specified where an analytical method, a documented purity limit or an audited procedure requires it. If you are unsure which side of that line your application sits on, tell us the application and we will spec the grade — that conversation costs nothing and it regularly saves people a tier.

Where does ammonia come from today?

From the air, not from dung. Industrial ammonia is synthesised by combining atmospheric nitrogen with hydrogen under high pressure and temperature over a catalyst — the Haber-Bosch route, which is why ammonia production is one of the largest single industrial consumers of energy on the planet and the foundation of nitrogen fertiliser. Aqueous ammonia is then made by dissolving that gas in water to the target concentration.

The scale of that shift is hard to overstate. For most of human history, usable nitrogen came from what had already been alive — manure, guano, and the dung heaps of Egyptian soot workshops. Fixing nitrogen directly out of the atmosphere severed that constraint, and the nitrogen atoms in a modern jug of aqueous ammonia have never been in an animal at all. They were in the air above the plant that made them.

Practically, that also means the product is consistent in a way the historical material never was. A salt recovered from burnt dung varied with the animals, the fuel and the operator. A synthesised gas dissolved to a specified concentration is the same liquid drum after drum, which is what makes a Certificate of Analysis meaningful rather than decorative.

The Egyptian soot workshops are gone, and so is the ambiguity about what the substance is. The name is the only part of the original story still in service — a word borrowed from a place nobody can agree on, for a salt that was probably something else, attached to a gas neither the namer nor the man who first caught it could have drawn the formula for.

Related reading

• Ammonium Hydroxide 29%: Complete Guide to Uses, Grades & Safety — the practical companion to this article.
• Who Discovered Chlorine? The 1774 Green Gas That Became Sodium Hypochlorite — the same year as Priestley, and the chemical you must never mix with this one.
• Who Discovered Phosphorus? Hennig Brand, 1669 — another product whose origin story is stranger than its datasheet.
• Potassium Hydroxide (KOH): Uses, Grades & Safety — the other strong base, and Davy's 1807 experiment on caustic potash.
• Chemicals for Copper Patina — where ammonia fumes do the work.

Key numbers and sources

Where sources disagree we have said so in the text rather than choosing the more quotable version: the year of Priestley's isolation (1773 or 1774), and whether the name derives from the sand, the temple or the district.