Synthetic nitrogen

Do not attempt this step because it is impressive. Legume rotation — a good ley fixes around 50–200 kg of nitrogen per hectare per year — manure, composted human waste, bone meal, fish waste, and by-product ammonia from coke ovens carry a settlement a long way at far less cost.

Measure whether they are enough: soil tests and yield records — see opening ground. Build synthetic nitrogen only when the records show nitrogen is what limits the harvest and the easier routes are fully used.

This is the hardest thing on this site. It needs hundreds of people, alloy steel fabrication, high-pressure engineering, reliable large power, gas purification, and continuous operation.

Atmospheric nitrogen is triple-bonded and extremely unreactive. Breaking it needs high temperature and high pressure and a catalyst — and high temperature works against the equilibrium, so only a fraction reacts each pass and unreacted gas must be recycled. A small group cannot do this. A regional industrial society can.

By electrolysis — the cleanest route, with no fossil input, needing roughly 50–55 kWh of electricity per kilogram of hydrogen — or from steam reforming of methane or water gas from coke.

Purify the feed gas thoroughly. Sulphur compounds poison the iron catalyst permanently, and oxygen compounds degrade it. Hydrogen burns across about 4–75% in air with a nearly invisible flame — leak-test every joint with soapy water, and ban ignition sources.

The pressure vessel is the real obstacle. The synthesis runs at roughly 150–300 atmospheres and 400–500 °C. At those conditions hydrogen diffuses into ordinary carbon steel and attacks the carbon, making it brittle — a vessel that looks sound fails without warning.

The historical solution was a double wall: an inner liner of low-carbon iron that hydrogen can pass through harmlessly, inside an outer pressure-bearing steel shell with vent holes so hydrogen escapes rather than building up. Use alloy steels resistant to hydrogen attack, hydraulically test every vessel above working pressure, and inspect it on a schedule.

Pass purified nitrogen and hydrogen in a 1:3 ratio over an iron catalyst promoted with small amounts of potassium and aluminium oxides. Only around 15% converts per pass: cool the gas to condense the ammonia out, then recycle the unreacted gas back through the converter.

Bleed off a small stream continuously so inert gases like argon do not build up in the loop. Log temperature, pressure and output continuously; a falling output at constant conditions means the catalyst is being poisoned.

Ammonia is a corrosive, suffocating gas. You smell it at a few parts per million; a few hundred ppm is immediately dangerous, and a large release kills downwind. It is stored as a liquid under pressure or refrigerated.

• Pressure-tested tanks, away from dwellings, with wind indicators so people know which way to move.
• Water sprays to knock down a release — ammonia dissolves readily in water.
• Respirators and eyewash at the plant.
• An evacuation plan: move crosswind and uphill.

Ammonia oxidised to nitric acid gives nitrates for fertiliser — and the same route leads to explosives. The two have shared a supply chain since the process was invented. Decide deliberately how that capability is governed: licensed production, records of every consignment, and secure storage.

Ammonium nitrate stores must be kept small, cool, dry, separated from fuels and combustibles, and inspected — large stockpiles have exploded with catastrophic loss of life, as at Texas City in 1947 and Beirut in 2020. Apply fertiliser by soil test, not by habit: excess nitrogen runs off, feeds algal blooms in rivers, and produces nitrous oxide, a potent greenhouse gas.